Electrical Performance Measurements of Solar Photovoltaic Cells and Arrays
Renewable energy generation is required to achieve net-zero energy buildings. Solar photovoltaic (PV) arrays typically offer the best means for providing this energy source. The decision of which photovoltaic product to select and how each system is designed, operated, and maintained depends, in large part, on the electrical performance information provided to the decision makers (e.g., the PV array owner, facilities manager, financer). Furthermore, additional utilization of 2nd and 3rd generation photovoltaic devices in conditions that differ from conventional bright outdoor light, such as applications in indoor/low light environments for powering internet-of-things sensors, installation where lighting is diffuse, or situations where operation is improved with concentrated illumination, requires new measurement scales and characterization methods. The creation of a NIST-designed and calibrated standard reference solar cell has established an SI-traceable reference instrument that will decrease the measurement uncertainty in electrical performance ratings of solar devices, thus giving more confidence to those specifying systems. This reference instrument is also a first step towards creating standard reporting conditions (SRC) other than the often-utilized “1-sun” or air mass 1.5 illumination condition. With the in-house development of the differential spectral responsivity method, performance of these NIST reference cells can be measured and calibrated under almost any lighting condition, enabling NIST to calibrate solar cells under unique conditions that no other laboratory in the world offers as of today. This effort also sets up NIST to lead a committee to write new standards on characterization of solar cells under non-standard reporting conditions. NIST will also complete work to capture high-quality performance data from field sites. Two sites that have previously been instrumented will be maintained as will a meteorological station. Data from the experiments will be published for use by outside researchers.
Description
Objective. To develop and improve the measurement science to: (1) accurately characterize the electrical and optical performance of solar photovoltaic cells, (2) design a standard reference cell with appropriate calibrations under a standard reporting condition or an ad-hoc reporting condition as deemed necessary by the end user, and (3) explore the efficiency of new generations of PV technologies under a variety of lighting conditions or for energy harvesting to power internet of things (IoT) devices.
What is the new technical idea? The technical ideas are to improve and implement state-of-the-art methods for characterizing PV cells and to develop standard reference instruments, measurement methods and new standards for the latest challenges in this field. NIST has been successful in developing (1) a hybrid monochromator light-emitting diode (LED) based spectral response measurement technique, (2) a new combinatorial-based method for evaluating a cell’s photocurrent versus irradiance relationship (leading to a patent granted in 2018), (3) a variety of solar simulators and temperature dependent I-V measurement stations for obtaining the electrical performance of single junction, multijunction, and other non-traditional PV cells and modules, (4) a custom hyperspectral imaging system capable of performing electroluminescence imaging of solar cells from micron scale to dimensions of up to 150 mm, and (5) an approach for quantifying the spectral dependence of charge carrier lifetimes. Progress has also been made on rounding out NIST’s eventual suite of PV cell characterization capabilities. With regard to a measurement service, a reference solar cell has been fabricated and tested, and a comprehensive uncertainty budget has been developed for it. Initially, the majority of the progress noted above was achieved while focusing on applications to single-junction, monocrystalline silicon (mono-Si) PV cells. However, in the last few years significant progress has been made towards measuring and characterizing other emerging PV technologies such as multijunction solar cells, and this work will continue. Additionally, novel PV materials that have improved performance under low light and non-standard reporting conditions are finding expanded use in powering sensors and controls for building operations, and work is needed to best capture their performance under the expected environmental conditions. In all cases, steps will be pursued that minimize the measurement uncertainties.
With regard to collecting field data, a very high quality set of PV and meteorological data has been collected over the last several years, and factors such as measurement redundancy, measurement resolution (i.e., at the module, string, and/or circuit levels), sampling frequency, data capture rates, and curation of the deployed instruments have been considered to produce a detailed and reliable data set. Such an approach allows the greatest utility for using the data for effectively evaluating and improving PV system simulation models, for providing datasets that can be confidently used when learning how to use commercially-available PV modeling tools, for analyzing the impact of local PV on the electrical grid and how to better estimate the local PV generation several minutes to a full day in advance, and for quantifying the impact of using data from more typical PV field monitoring systems when investigating issues such as fault detection and service lifetime predictions. A large amount of this dataset has been published to a public website, (https://pvdata.nist.gov/), and more of that data will be evaluated and made ready for online dissemination or directly to collaborators over the next year.
What is the research plan? Efforts will continue to establish a NIST measurement service for calibration of 20 mm x 20 mm, silicon-based reference solar cells under the standard reporting conditions (SRC) through the use of the spectral response measurement system. The FOCUS in FY 21 will be on developing a proposal for a new measurement service and submitting it to the Measurement Services Council for approval and subsequent development. Also, additional improvements to the current measurement system will be made such as a better quantification of the repeatability component of the uncertainty budget and use of the new automated scanning stages to improve the calibration procedure and methodology. The scanning stage can also facilitate other types of diagnostic measurements such as mapping out the uniformity of the external quantum efficiency response of solar cells. Measuring the uniformity can help reduce measurement uncertainties and this topic will be explored in more detail.
In addition to the reference cell work, steady progress has also been made on multijunction solar cell measurements. In FY 20, a complete custom multizone solar simulator was designed, fabricated and tested, complete with an XY programmable moving stage. A comprehensive LabVIEW based program was written for measuring irradiance levels using multiple reference cells, adjusting the synthesized spectra and performing I-V curve measurements. The FY 21 efforts will FOCUS on comprehensive measurement of various multijunction solar cells using this new set up and verifying that it can accurately measure the performance of multijunction solar cells. Test cells for inter-lab comparisons have already been acquired and will be used to further validate the efficacy of this system.
In FY 20, our new hyperspectral imaging system was used extensively for the first time to measure PV data on both multijunction and single junction solar cells using in the electroluminescence mode. The results of these early measurements were extremely encouraging and we performed some baseline calibration measurements to obtain absolute electroluminescence data. In FY 21, we intend to continue such measurements on more variety of solar cells. Furthermore, a new optical cryostat will be delivered to NIST in the fall of 2020, which will allow us to perform temperature dependent measurements, providing additional data for modeling and understanding of various PV phenomena. We will also be using the newly added photoluminescence capability with laser illumination to study a range of effects that were previously inaccessible to us. Finally, we will collaborate with Division 731 to study formation of defects or degradation phenomena in field-induced or artificially-degraded solar PV modules.
Energy harvesting from ambient lighting conditions for the purpose of providing power for IoT sensors and devices is a new area that will continue to be explored in more depth in FY21, building on the success of the FY19 Exploratory Project. In FY 20, we published a paper outlining steps for a new method for measuring the performance of solar cells under indoor ambient lighting. We also performed an inter-lab measurement comparison with an international partner that exposed certain deficiencies in the early standards and test protocols. We intend to address these issues further in FY21 with more testing of solar cells under various lighting conditions and by doing more inter-lab measurements. Other issues to consider are temperature effects, angular effects and some modeling to address discrepancies between experimental results and various diode-based current-voltage models. We will also be setting up apparatus to measure and record irradiance and temperature data within a residential or commercial building for the purpose of forming a complete database that can be used for modeling and predicting available light energy inside buildings over an extended time.
Finally, as the PV field data collection efforts begin to ramp down, the team will maintain some core capabilities such as the weather station and roof-top I-V and irradiance measurements while it will work with existing internal and external collaborators to complete collection, compiling, reducing, and making available quality data for various research and modeling needs.
Major Accomplishments
Outcomes:
- One year of high-fidelity data collected that quantifies the performance of three photovoltaic systems installed in the NIST campus
- Draft revision of ASTM Standard E1021-06, Standard Test Method for Spectral Responsivity Measurements of Photovoltaic Devices.
A review of primary technologies of thin-film solar cells
Thin-film solar cells are preferable for their cost-effective nature, least use of material, and an optimistic trend in the rise of efficiency. This paper presents a holistic review regarding 3 major types of thin-film solar cells including cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and amorphous silicon (α-Si) from their inception to the best laboratory-developed module. The remarkable evolution, cell configuration, limitations, cell performance, and global market share of each technology are discussed. The reliability, availability of cell materials, and comparison of different properties are equally explored for the corresponding technologies. The emerging solar cell technologies holding some key factors and solutions for future development are also mentioned. The summarized part of this comparative study is targeted to help the readers to decipher possible research scopes considering proper applications and productions of solar cells.
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Introduction
In our solar system, the Sun is the most powerful light source that also happens to be the most accessible and inexpensive source of energy. The generated energy from solar does not produce any harmful emission thus reduces carbon dioxide (CO2) generation, which is one of the greatest advantages of using solar energy. It is also found that energy used by humans in a year is proportional to the Sunlight striking the Earth for an hour [1]. The photovoltaic (PV) transformation of sunlight into power is the most reliable system to fulfill future energy demand. This technology can also provide an effective solution to the mass destruction of nature.
The solar cell is a photovoltaic device—typically consisting of specifically prepared Silicon (Si) layers. The design of solar cells functions for the conversion of photons into electricity. The sunlight, consisting photons have enough energy to galvanize electrons in a semiconductor device to travel from lower to higher energy level creating electron-hole pairs. Generally, the electron flow from one to another layer of a junction by photoelectric effect creates a voltage difference and provides energy to another circuit. The amount of electricity created in a cell depends on some factors such as the size of the cell, quality of the light source, and materials used for creating the device.
It has been a while that crystalline silicon (c-Si) showed its value in the market with advantages including high performance (∼26.7%), ease of fabrication, and environmentally friendly traits [2]. Longevity is also a considerable advantage because c-Si modules deployed in the 1970s are still operating. Additionally, single-crystal panels can withstand the rough conditions accustomed to space travel [3]. Ironically, c-Si happens to be a poor light absorber along with an inflexible and fairly fragile when in an unordered amorphous structure. These solar cells are specifically used at places of high-performance requirements. The primary dissimilarity between thin-film and c-Si solar cells lies in the flexible pairing of PV materials. Thin-film solar cells are cheaper than mature c-Si wafer cells (sheets). over, thin films are easier to handle and more flexible. They are also less vulnerable to destruction than their Si competitors. Although thin-film solar materials have slightly lower efficiency (η), they can outweigh the cost-benefit considering various applications.
To mitigate the issues regarding solar cell materials, several research groups collaborated on intensive experimental works. There are different types of separate works of literature available on the advances of solar cells regarding amorphous silicon (α-Si) [4], copper indium gallium selenide (CIGS) [5], and cadmium telluride (CdTe) [6]. Though some review papers reported several prominent technologies such as Lee and Ebong [2] and Kowsar et al [7], a single report consisting of all the aspects (efficiencies, developments, structure, specifications, and limitations) is not available. For this reason, a compact, well-organized, and informative paper with distinctive categories among the classifications will be highly beneficial for the best reading ability. As such, this paper delivers an outline of each state-of-the-art technology with all the features stated above on 3 primary kinds of thin-film solar cells.
In this document, we briefly reviewed thin-film solar cell technologies including α-Si, CIGS, and CdTe, commencing with the gradual development of the corresponding technologies along with their structural parameters and issues in section 2, which was then followed by the commercial module distribution of thin-film solar cells in comparison to c-Si in section 3. In section 4, we compared the devices’ properties followed by section 5 that highlighted the next-generation technologies such as a dye-sensitized solar cell (DSSC), perovskite solar cell (PSC), organic solar cell (OSC), and quantum dot solar cell (QDSC). In section 6 we finalized and emphasized the noticeable achievements based on the analysis.
Thin film photovoltaics
Thin-film solar cell (TFSC) is a 2nd generation technology, made by employing single or multiple thin layers of PV elements on a glass, plastic, or metal substrate. The thickness of the film can vary from several nanometers to tens of micrometers, which is noticeably thinner than its opponent, the traditional 1st generation c-Si solar cell (∼200 μm thick wafers). This is why thin-film solar cells are amenable, lower in mass, and have limited resistance or abrasion [8–10].
2.1. Amorphous silicon solar cell
In the beginning, the α-Si solar cell used to be deposited in p-i-n structure but the device is likewise to be fabricated as an n-i-p formation sequence as well [7]; the historical progressions of α-Si solar cells are recapitulated in figure 1 and table 1 below.
Table 1. Sequential developments of α-Si solar cell.
| 1976–1977 | The 1st hydrogenated-α-Si (α-Si:H) solar cell was developed in a p-i-n formation employing doping gases while discharging. | 2.4% (S) | Carlson and Wronski at RCA Laboratories [11, 12] |
| Using Schottky barrier formation with 1.1 eV barrier heights for platinum (Pt) cells, close-ideal diode behavior was acquired. | 4% (S) | ||
| 1978 | Combined Schottky barrier formation with an insulating layer in metal-to-semiconductor (M–I–S) junction. The insulation layer was adjusted to equilibrate the low work function of inexpensive metal (nickel). | 4.8% (S) | Wilson and McGill at Heriot-Watt University, UK [13] |
| 1980 | The p-i-n formation with a 1.19 cm 2 area was fabricated to decrease the loss characterizations. | 6.1% (S) | Carlson at RCA Laboratories [14] |
| 1981–1982 | Hydrogenated-amorphous silicon carbide (α-SiC:H) was produced by [SiH4(1−X)CH4(X)] plasma decomposition with diborane (B2H6) or phosphine (PH3) dopant gas. The α-SiC:H/α-Si:H heterojunction device was created with 887 mV open-circuit voltage (Voc), 12.33 mA cm −2 short-circuit current (Jsc), and 0.653 fill-factor (FF). The fabricated structure became more successful with Voc = 880 mV, Jsc = 15.21 mA cm −2. and FF = 0.601. | 7.14% (S) 8.04% (S) | Tawada et al at Osaka University, Japan [15, 16] |
| 1986 | The insertion of a thin-film at the p-i interface affected short wavelength and performance with FF (0.771). | 8.43% (S) | Arya et al at Solarex Corporation, USA [17] |
| 1986 | Glass substrate without anti-reflection coating (ARC) resulted Voc = 12670 mV, Jsc = 78.47 mA cm −2. and FF = 0.667. | 9.63% (S) | Yamazaki et al at SEL [18] |
| 1992 | The double‐junction with the dual‐bandgap device was fabricated employing an appropriate deposition method. | 11% (M) | Guha et al at USSC [19] |
| 1996–1997 | A dual-junction structure of α-Si:H/α-Si:Ge with the decreased bandgap-alloyed device. Employed α-Si-based alloy in spectrum-splitting, triple-junction formation. Improved amorphous silicon germanium (α-SiGe) alloy, p-n tunnel junction, and top conducting oxide (TCO). | 11.8% (M) 13% (M) | Yang et al at USSC [20, 21] |
| 2013 | Developed a triple-junction device using α-Si:H/μc-Si:H/μc-Si:H formation. | 13.4% (M) | Kim et al at LGEARI [22] |
| 2015–2016 | By diode and triode plasma-enhanced chemical vapor deposition (PECVD), α-Si:H was fabricated at different rates. Decreasing deposition rates slightly lowered light-induced degradation. Decreased metastable defect and increased bandgap were attributed to deposition rates (1–3 × 10 –2 nm s −1 ) and triode PECVD. | 10.22% (S) | Matsui and Sai at AIST [23–25] |
| Similarly α-Si:H/μc-Si:H tandem device was produced. | 12.69% (M) | ||
| Higher Jsc (32.9 mA cm −2 ) was acquired from a periodically textured substrate and incorporated for a triple-junction. | 13.6% (M) | ||
| After equalizing Jsc and FF, light-induced degradation was minimized (4%). | 14.04% (M) |
S: single-junction; M: multi-junction (micromorph)RCA: Radio Corporation of America, USA; SEL: Semiconductor Energy Laboratory, Japan; USSC: United Solar System Corporation, USA; LGEARI: LG Electronics Advanced Research Institute, Korea; AIST: National Institute for Advanced Industrial Science Technology, Japan
2.1.1. Structure of a-Si
This solar cell with a random crystal structure is usually developed on a fluorine (F)-doped tin oxide (SnO2:F) fabricated glass substrate for single-junction or periodically (honeycomb)-textured substrate (HTS) for micromorph (tandem) structure. To reduce reflective loss and increase conductivity, normally silver (Ag) and gallium (Ga)-doped zinc oxide (ZnO:Ga) coatings are applied on the substrate, successively. Then hydrogenated-α-Si (α-Si:H) is generally deposited by a diode or triode plasma-enhanced chemical vapor deposition (PECVD) employing CO2, phosphine (PH3), diborane (B2H6), silane (SiH4), and hydrogen (H2) dopant gases. After this process, transparent conducting oxide (TCO) film as the front window is deposited typically of indium tin oxide (In2O3:Sn) or hydrogenated-indium oxide (In2O3:H) (IOH) by radio frequency (RF) magnetron sputtering. As the grid electrode, Ag can be deployed, following which, a moth-eye-based anti-reflection coating (ARC) can also be applied to improve cell performance [25].
In the latest technology, the single-junction [SLG/Ag/GZO/(n)α-Si:H/(i)α-Si:H(diode/triode)/(p)α-Si:H/ITO/Ag] device was fabricated by diode PECVD, where the tandem (triple-junction) [HTS/Ag/GZO/μc-Si:H/μc-Si:H/a-Si:H(diode/triode)/IOH/Ag] device was fabricated by triode PECVD. For the triple-junction module, reactive ion etching was used for isolating the cells along with nano-crystalline silicon oxide (nc-SiOx) layers. The device was arranged with a hydrogenated-micro-crystalline Si (μc-Si:H) as the bottom (∼1.8 μm thick), a μc-Si:H as the middle (∼1.6 μm thick), and a α-Si:H as the top (∼230 nm thick) cell. Each of the μc-Si:H cells were stacked as the given substrate type arrangement: (n)μc-Si:H/(n)nc-SiOX/(i)μc-Si:H/(p)nc-SiOX/(p)μc-Si:H [25]. Figure 2 demonstrates the state-of-the-art layout of a triple-junction n-p α-Si:H/μc-Si:H/μc-Si:H solar cell.
2.1.2. Specifications of a-Si
Table 2 displays the latest α-Si solar cell parameters.
Table 2. Latest α-Si solar cell parameters [25].
| 2016 | 1.05 | 1922 | 9.94 | 0.734 | 14.04 | AIST |
2.1.3. Limitations of a-Si
Our identified critical issues regarding α-Si solar cells are:
The deposition process requires improvement that is important for the large-scale manufacturing of this solar cell [26].
Light scattering properties have to be dealt with by improving the optoelectronic properties of the front TCO component [27].
Staebler-Wronski effect needs to be resolved by finding a suitable way to impede the light-induced degradation of the device structure [28].
In the case of the α-Si:H solar cell, due to the creation of an electron-hole pair by an absorbed photon in the intrinsic layer, the electric field induced across the intrinsic layer causes electrons to drift to n-layer and holes to p-layer. A thin graded interface layer is usually employed to reduce the p/i interface defects—responsible for low open-circuit voltage (Voc) and short-circuit current (Jsc), to improve cell performance.
2.2. Copper indium gallium selenide solar cell
In the beginning, the CIGS solar cell was a plain p-CuInSe2/n-CdS heterojunction [29] but the device structure has been configured towards substrate/Mo/CIGS/CdS/ZnO/AZO/Al formation mostly [30, 31]; the historical progressions of CIGS solar cells are recapitulated in figure 3 and table 3 below.
Table 3. Sequential developments of CIGS solar cell.
| 1976–1977 | The 1st CIGS solar cells were developed through 2 modes of 100 mW cm −2 tungsten-halogen illuminations for 1.2 cm 2 (p-CuInSe2/n-CdS) devices. | 4.5% (R) | Kazmerski et al at University of Maine, USA [29, 32] |
| Heterojunction materials including ternary (CuInSe2, CuInS2, CuInTe2) and binary indium phosphide (InP) with cadmium sulfide (CdS) were fabricated by vacuum deposition. | 5.7% (R) | ||
| 1980–1982 | Polycrystalline CdS/CuInSe2 heterojunction device was produced by continuous material evaporation to deposit copper indium diselenide (CuInSe2) layer and showed an increased Jsc (31 mA/cm 2 ) for 1 cm 2 device. | 5.7% (R) | Mickelsen and Chen at Boeing Aerospace Company, USA [33–36] |
| The device was constructed by vacuum deposition and sputtering on cheap substrates. | 7.5% (R) | ||
| The Jsc was 35 mA cm −2 and the film thickness was 5 μm. | 9.5% (R) | ||
| Mixed ZnxCd1−XS used to enhance Voc. | 10.6% (R) | ||
| 1985 | Introduced zinc oxide (ZnO) combining p-CuInSe2 with thin undoped (Cu,Zn)S or CdS. The n-CdS film harvested photons with sc by 25%. | 11.2% (R) | Potter et al at ARCO Solar Inc., USA [37] |
| 1988 | The ZnO/CdS/CIS cell was analyzed to find that tunneling and series resistance controlled low-temperature characteristics, where recombination limited cell efficiency. | 12.2% (R) | Mitchell and Liu at ARCO Solar Inc., USA [38] |
| 1990 | Polycrystalline ZnO/CdZnS/CuInGaSe2 device was fabricated through employing CuInGaSe2 by Physical Vapor Deposition (PVD), CdZnS by chemical vapor deposition (CVD), and ZnO by reactive sputtering. | 12.5% (R) | Devany et al at Boeing Aerospace and Electronics, USA [39] |
| 1993 | CuInGaSe2 was obtained by electron (E)-beam evaporated layers with hydrogen selenide (H2Se) gas reaction at 400°C, where molybdenum (MO), titanium (Ti), and aluminum (Al) were substrates. | 8.3% (F) | Başol et al at ISET [40] |
| 1993 | Polycrystalline CuIn(1−x)GaxSe2 device was made by material evaporation of selenide (Se), chemical deposition of cadmium zinc sulfide (CdZnS) (20–30 nm), and radio-frequency (RF) sputtering of transparent conducting oxide (TCO) ZnO layer. The gallium (Ga)-rich cell and reduced optical losses caused the improvement. | 13.7% (R) | Chen et al at Boeing Defense and Space Group, USA [41] |
| 1994–1995 | CuInxGa(1−x)Se2 was built from (Inx,Ga1−x)2Se3 precursor layers by co-evaporating indium (In), Ga, and Se. The cell was exposed to a flux of copper (Cu) and Se. | 15.9% (R) | Gabor and Tuttle et al at NREL [42, 43] |
| The integration of Ga in Cu(In,Ga)Se2 device increased the absorber layer bandgap, Voc (654 mV), and FF (0.77). | 17.1% (R) | ||
| 1996 | Less temperature with the polymeric substrate was employed for depositing CdS window layer and ZnO. | 9.3% (F) | Başol et al at ISET [44] |
| 1996 | Grid design modifications were done, where the intrinsic ZnO (i-ZnO) layer was critical for developing the cell. | 17.7% (R) | Tuttle et al at NREL [45] |
| 1999 | With no buffer layer, a cadmium (Cd)-free cell was fabricated by PVD and direct ZnO deposition on Cu(In,Ga)Se2 layer. | 15% (R) | Contreras et al at NREL [46] |
| The ZnO/CdS/Cu(In,Ga)Se2/Mo polycrystalline cell led to further improvement. | 18.8% (R) | ||
| 2003 | Improved ZnO/CdS/CuInGaSe2 device was obtained due to more characterization. | 19.2% (R) | Ramanathan et al at NREL [47] |
| 2005 | Cu(In,Ga)Se2 device improvement was attributed to absorber bandgap (1.14 eV), decreased diode saturation current density (3 × 10 –8 mA cm −2 ), diode quality (1.30 | 19.5% (R) | Contreras et al at NREL [48] |
| 2008 | Deposition recombination was reduced for process termination with Ga-poor (In-rich) film. | 19.9% (R) | Repins et al at NREL [49] |
| 2010 | Maximum efficiency gained using Mo flexible substrate by a 3-stage co-evaporation process. | 14.6% (F) | Niki et al at AIST [50] |
| 2010 | Recorded more improved Cu(In,Ga)Se2 thin cell. | 20.1% (R) 20.3% (R) | Jackson et al at ZSW [51] |
| 2011–2012 | Stainless-steel (SS) substrate temperature was reduced while depositing CIGS. | 17.1% (F) | Reinhard and Pianezzi et al at EMPA [52, 53] |
| Employing CIGS growth further enhanced performance. | 17.7% (F) | ||
| 2013 | The highest efficiency was gained for polymer foil substrate. | 20.4% (F) | EMPA and FhG-ISE [54] |
| 2013–2014 | Generated Cu(In,Ga)Se2 devices by static co-evaporation process and employing Zn(O,S) buffer layers. | 20.4% (R) | Powalla and Jackson et al at ZSW [55, 56] |
| Potassium (K)-doped film increased Ga material. | 20.8% (R) | ||
| 2014 | With high deposition rates and co-evaporation of the CIGS absorber film, the performance was improved. | 21% (R) | Herrmann et al at Solibro Hi-Tech GmbH, Germany [57] |
| 2014 | An improved efficiency was reported. | 21.7% (R) | Jackson et al at ZSW [58] |
| 2015 | The CIS absorber layer and junction creation were improved. | 22.3% (R) | Solar Frontier and ZSW [59] |
| 2016 | Employing alkali substances rubidium (Rb) and cesium (Cs) in alkali post-deposition treatment (PDT) actuated the alkali material process in the absorber and improved diode quality. | 22.6% (R) | Jackson et al at ZSW [60] |
| 2017 | Using alkali element Cs and modifying the absorber layer allowed a wider bandgap thus reverse saturation current density was improved. | 22.9% (R) | Wu et al at AIST [61] |
| 2019 | Using the roll-to-cell process, the device was fabricated on a SS foil substrate. | 20.56% (F) | Bayman et al at NREL [62] |
| 2019 | A Cd-free Zn(O,S,OH)x/Zn0.8Mg0.2O double-buffer layer Cu(In,Ga)(Se,S)2 device was generated by chemical bath deposition (CBD) and atomic layer deposition (ALD). | 23.35% (R) | Nakamura et al at AIST [63] |
R: rigid substrate; F: flexible substrate (polymeric).ISET: International Solar Electric Technology, USA; NREL: National Renewable Energy Laboratory, USA; ZSW: The Center for Solar Energy Hydrogen Research, Germany; EMPA: Swiss Federal Laboratories for Materials Science Technology, Switzerland; FhG-ISE: Fraunhofer Institute for Solar Energy Systems, Germany.
2.2.1. Structure of CIGS
This solar cell with a chalcopyrite crystal structure is usually developed on ultrasonically washed and dried rigid substrates; moreover, polymeric flexible substrates are also being used [64]. Molybdenum (Mo)-as a back contact as well as the reflector of most unabsorbed light, is normally sputtered on a soda-lime glass (SLG) substrate. The absorber layer, Cu(In,Ga)(Se,S)2 (∼2 μm thick) is created by physical vapor deposition (PVD) for sulfurization-after-selenization (SAS) of the precursor layers generally by hydrogen selenide (H2Se) gas that naturally gives rise to Mo(S,Se)x film between the absorber and back contact. At times, applied cesium (Cs) treatment thermally evaporated cesium fluoride (CsF) on the absorber layer, following which cadmium sulfide (CdS) (∼50 nm thick) or cadmium (Cd)-free buffer layer typically through chemical bath deposition (CBD) is placed on top [63]. Then an intrinsic zinc oxide (i-ZnO) (∼100 nm thick) layer covered by aluminum (Al)-doped ZnO (ZnO:Al) as TCO layer is fabricated on CdS buffer by chemical vapor deposition (CVD) to avoid external damage [65].
In the latest technology, a 2nd buffer layer of magnesium (Mg)-doped ZnO (ZnO:Mg) (∼50 nm thick) was fabricated by atomic layer deposition (ALD) on the 1st Cd-free Zn(O,S,OH)x (∼50 nm thick) buffer to enhance the cell performance. Whereas, Metal-organic CVD (MOCVD) was used to deposit the boron (B)-doped ZnO (ZnO:B) layer as TCO. After that Al and magnesium fluoride (MgF2) were evaporated through electron (E)-beam evaporation for producing the electrode and ARC, correspondingly. The ratio of Ga to (GaIn) was around 0.3, where metal compositions like this were deposited with an additive such as sodium (Na) to form the precursor layers [63]. Figure 4 demonstrates the state-of-the-art layout of a rigid-substrate double-buffer CIGSSe solar cell.
2.2.2. Specifications of CIGS
Table 4 displays the latest CIGS solar cell parameters.
Table 4. Latest CIGS solar cell parameters [63].
| 2019 | 1.04 | 734 | 39.60 | 0.804 | 23.35 | AIST |
Types of Solar Panels: Pros and Cons
Emily Rhode is a science writer, communicator, and educator with over 20 years of experience working with students, scientists, and government experts to help make science more accessible and engaging. She holds a B.S. in Environmental Science and an M.Ed. in Secondary Science Education.
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There are three main types of solar panels commercially available: monocrystalline solar panels, polycrystalline solar panels, and thin-film solar panels. There are also several other promising technologies currently in development, including bifacial panels, organic solar cells, concentrator photovoltaics, and even nano-scale innovations like quantum dots.
Each of the different types of solar panels has a unique set of advantages and disadvantages that consumers should consider when choosing a solar panel system.
Monocrystalline solar cells are slower and more expensive to produce than other types of solar cells due to the precise way the silicon ingots must be made. In order to grow a uniform crystal, the temperature of the materials must be kept very high. As a result, a large amount of energy must be used because of the loss of heat from the silicon seed that occurs throughout the manufacturing process. Up to 50% of the material can be wasted during the cutting process, resulting in higher production costs for the manufacturer.
But these types of solar cells maintain their popularity for a number of reasons. First, they have a higher efficiency than any other type of solar cell because they are made of a single crystal, which allows electrons to flow more easily through the cell. Because they are so efficient, they can be smaller than other solar panel systems and still generate the same amount of electricity. They also have the longest life span of any type of solar panel on the market today.
One of the biggest downsides to monocrystalline solar panels is the cost (due to the production process). In addition, they are not as efficient as other types of solar panels in situations where the light does not hit them directly. And if they get covered in dirt, snow, or leaves, or if they are operating in very high temperatures, their efficiency declines even more. While monocrystalline solar panels remain popular, the low cost and rising efficiency of other types of panels are becoming increasingly appealing to consumers.
Polycrystalline Solar Panels
As the name implies, polycrystalline solar panels are made of cells formed from multiple, non-aligned silicon crystals. These first-generation solar cells are produced by melting solar grade silicon and casting it into a mold and allowing it to solidify. The molded silicon is then sliced into wafers to be used in a solar panel.
Polycrystalline solar cells are less expensive to produce than monocrystalline cells because they do not require the time and energy needed to create and cut a single crystal. And while the boundaries created by the grains of the silicon crystals result in barriers for efficient electron flow, they are actually more efficient in low-light conditions than monocrystalline cells and can maintain output when not directly angled at the sun. They end up having about the same overall energy output because of this ability to maintain electricity production in adverse conditions.
The cells of a polycrystalline solar panel are larger than their monocrystalline counterparts, so the panels may take up more space to produce the same amount of electricity. They are also not as durable or long-lasting as other types of panels, although the differences in longevity are small.
Thin-Film Solar Panels
The high cost of producing solar-grade silicon led to the creation of several types of second- and third-generation solar cells known as thin-film semiconductors. Thin-film solar cells need a lower volume of materials, often using a layer of silicon as little as one micron thick, which is about 1/300th of the width of mono- and polycrystalline solar cells. The silicon is also of lower quality than the kind used in monocrystalline wafers.
Many solar cells are made from non-crystalline amorphous silicon. Because amorphous silicon does not have the semiconductive properties of crystalline silicon, it must be combined with hydrogen in order to conduct electricity. Amorphous silicon solar cells are the most common type of thin-film cell, and they are often found in electronics like calculators and watches.
Other commercially viable thin-film semiconductor materials include cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and gallium arsenide (GaAs). A layer of semiconductor material is deposited on an inexpensive substrate like glass, metal, or plastic, making it cheaper and more adaptable than other solar cells. The absorption rates of the semiconductor materials are high, which is one of the reasons they use less material than other cells.
Production of thin-film cells is much simpler and faster than first-generation solar cells, and there are a variety of techniques that can be used to make them, depending on the capabilities of the manufacturer. Thin-film solar cells like CIGS can be deposited on plastic, which significantly reduces its weight and increases its flexibility. CdTe holds the distinction of being the only thin film that has lower costs, higher payback time, lower carbon footprint, and lower water use over its lifetime than all other solar technologies.
However, the downsides of thin-film solar cells in their current form are numerous. The cadmium in CdTe cells is highly toxic if inhaled or ingested, and can leach into the ground or water supply if not properly handled during disposal. This could be avoided if the panels are recycled, but the technology is currently not as widely available as it needs to be. The use of rare metals like those found in CIGS, CdTe, and GaAs can also be an expensive and potentially limiting factor in producing large amounts of thin-film solar cells.
Other Types
The variety of solar panels is much greater than what is currently on the commercial market. Many newer types of solar technology are in development, and older types are being studied for possible increases in efficiency and decreases in cost. Several of these emerging technologies are in the pilot phase of testing, while others remain proven only in laboratory settings. Here are some of the other types of solar panels that have been developed.
Bifacial Solar Panels
Traditional solar panels only have solar cells on one side of the panel. Bifacial solar panels have solar cells built on both sides in order to allow them to collect not only incoming sunlight, but also albedo, or reflected light off the ground beneath them. They also move with the sun in order to maximize the amount of time that sunlight can be collected on either side of the panel. A study from the National Renewable Energy Laboratory showed a 9% increase in efficiency over single-sided panels.
Concentrator Photovoltaic Technology
Concentrator photovoltaic technology (CPV) uses optical equipment and techniques such as curved mirrors to concentrate solar energy in a cost-efficient way. Because these panels concentrate sunlight, they do not need as many solar cells to produce an equal amount of electricity. This means that these solar panels can use higher quality solar cells at a lower overall cost.
Organic Photovoltaics
Organic photovoltaic cells use small organic molecules or layers of organic polymers to conduct electricity. These cells are lightweight, flexible, and have a lower overall cost and environmental impact than many other types of solar cells.
Perovskite Cells
The Perovskite crystalline structure of the light-collecting material gives these cells their name. They are low cost, easy to manufacture, and have a high absorbance. They are currently too unstable for large-scale use.
Dye-Sensitized Solar Cells (DSSC)
These five-layered thin-film cells use a special sensitizing dye to help the flow of electrons which creates the current to produce electricity. DSSC have the advantage of working in low light conditions and increasing efficiency as temperatures rise, but some of the chemicals they contain will freeze at low temperatures, which makes the unit inoperable in such situations.
Quantum Dots
This technology has only been tested in laboratories, but it has shown several positive attributes. Quantum dot cells are made from different metals and work on the nano-scale, so their power production-to-weight ratio is very good. Unfortunately, they can also be highly toxic to people and the environment if not handled and disposed of properly.
Almost all solar panels sold commercially are monocrystalline, common because they’re so compact, efficient, and long-lasting. Monocrystalline solar panels are also proven to be more durable under high temperatures.
Monocrystalline solar panels are the most efficient, with ratings ranging from 17% to 25%. In general, the more aligned the silicon molecules of a solar panel are, the better the panel will be at converting solar energy. The monocrystalline variety has the most aligned molecules because it’s cut from a single source of silicon.
Thin-film solar panels tend to be the cheapest of the three commercially available options. This is because they’re easier to manufacture and require less materials. However, they also tend to be the least efficient.
Some may choose to buy polycrystalline solar panels because they’re cheaper than monocrystalline panels and less wasteful. They’re less efficient and bigger than their more common counterparts, but you might get more bang for your buck if you have abundant space and access to sunshine.
Thin-film solar panels are lightweight and flexible, so they can better adapt to unconventional building situations. They’re also much cheaper than other types of solar panels and less wasteful because they use less silicon.
- Luceño-Sánchez, José Antonio, et al. Materials for Photovoltaics: State of Art and Recent Developments. International Journal of Molecular Sciences, vol. 20, no. 4, 2019, pp. 976., doi:10.3390/ijms20040976
- Solar Photovoltaic Cell Basics. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.
- Qazi, Salahuddin. Standalone Photovoltaic (PV) Systems for Disaster Relief and Remote Areas. Elsevier, 2017., doi:10.1016/C2014-0-03107-3
- Bayod-Rújula, Angel Antonio. Chapter 8—Solar Photovoltaics (PV). Solar Hydrogen Production: Processes, Systems and Technologies, 2019, pp. 237-295., doi:10.1016/B978-0-12-814853-2.00008-4
- Taraba, Michal. Properties Measurement of the Thin Film Solar Panels Under Adverse Weather Conditions. Transportation Research Procedia, vol. 40, 2019, pp. 535-540., doi:10.1016/j.trpro.2019.07.077
- Bagher, Askari Muhammed, et al. Types of Solar Cells and Applications. American Journal of Optics and Photonics, vol. 3, no. 5, 2015, pp. 94-113., doi:10.11648/j.ajop.20150305.17
- Project Profile: Performance Models and Standards for Bifacial PV Module Technologies. U.S. Department of Energy.
- Bifacial Solar Advances With the Times—and the Sun. National Renewable Energy Laboratory.
- Current Status of Concentrator Photovoltaic (CPV) Technology. National Renewable Energy Laboratory.
Types of Solar Panels: Pros and Cons
Emily Rhode is a science writer, communicator, and educator with over 20 years of experience working with students, scientists, and government experts to help make science more accessible and engaging. She holds a B.S. in Environmental Science and an M.Ed. in Secondary Science Education.
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There are three main types of solar panels commercially available: monocrystalline solar panels, polycrystalline solar panels, and thin-film solar panels. There are also several other promising technologies currently in development, including bifacial panels, organic solar cells, concentrator photovoltaics, and even nano-scale innovations like quantum dots.
Each of the different types of solar panels has a unique set of advantages and disadvantages that consumers should consider when choosing a solar panel system.
Monocrystalline solar cells are slower and more expensive to produce than other types of solar cells due to the precise way the silicon ingots must be made. In order to grow a uniform crystal, the temperature of the materials must be kept very high. As a result, a large amount of energy must be used because of the loss of heat from the silicon seed that occurs throughout the manufacturing process. Up to 50% of the material can be wasted during the cutting process, resulting in higher production costs for the manufacturer.
But these types of solar cells maintain their popularity for a number of reasons. First, they have a higher efficiency than any other type of solar cell because they are made of a single crystal, which allows electrons to flow more easily through the cell. Because they are so efficient, they can be smaller than other solar panel systems and still generate the same amount of electricity. They also have the longest life span of any type of solar panel on the market today.
One of the biggest downsides to monocrystalline solar panels is the cost (due to the production process). In addition, they are not as efficient as other types of solar panels in situations where the light does not hit them directly. And if they get covered in dirt, snow, or leaves, or if they are operating in very high temperatures, their efficiency declines even more. While monocrystalline solar panels remain popular, the low cost and rising efficiency of other types of panels are becoming increasingly appealing to consumers.
Polycrystalline Solar Panels
As the name implies, polycrystalline solar panels are made of cells formed from multiple, non-aligned silicon crystals. These first-generation solar cells are produced by melting solar grade silicon and casting it into a mold and allowing it to solidify. The molded silicon is then sliced into wafers to be used in a solar panel.
Polycrystalline solar cells are less expensive to produce than monocrystalline cells because they do not require the time and energy needed to create and cut a single crystal. And while the boundaries created by the grains of the silicon crystals result in barriers for efficient electron flow, they are actually more efficient in low-light conditions than monocrystalline cells and can maintain output when not directly angled at the sun. They end up having about the same overall energy output because of this ability to maintain electricity production in adverse conditions.
The cells of a polycrystalline solar panel are larger than their monocrystalline counterparts, so the panels may take up more space to produce the same amount of electricity. They are also not as durable or long-lasting as other types of panels, although the differences in longevity are small.
Thin-Film Solar Panels
The high cost of producing solar-grade silicon led to the creation of several types of second- and third-generation solar cells known as thin-film semiconductors. Thin-film solar cells need a lower volume of materials, often using a layer of silicon as little as one micron thick, which is about 1/300th of the width of mono- and polycrystalline solar cells. The silicon is also of lower quality than the kind used in monocrystalline wafers.
Many solar cells are made from non-crystalline amorphous silicon. Because amorphous silicon does not have the semiconductive properties of crystalline silicon, it must be combined with hydrogen in order to conduct electricity. Amorphous silicon solar cells are the most common type of thin-film cell, and they are often found in electronics like calculators and watches.
Other commercially viable thin-film semiconductor materials include cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and gallium arsenide (GaAs). A layer of semiconductor material is deposited on an inexpensive substrate like glass, metal, or plastic, making it cheaper and more adaptable than other solar cells. The absorption rates of the semiconductor materials are high, which is one of the reasons they use less material than other cells.
Production of thin-film cells is much simpler and faster than first-generation solar cells, and there are a variety of techniques that can be used to make them, depending on the capabilities of the manufacturer. Thin-film solar cells like CIGS can be deposited on plastic, which significantly reduces its weight and increases its flexibility. CdTe holds the distinction of being the only thin film that has lower costs, higher payback time, lower carbon footprint, and lower water use over its lifetime than all other solar technologies.
However, the downsides of thin-film solar cells in their current form are numerous. The cadmium in CdTe cells is highly toxic if inhaled or ingested, and can leach into the ground or water supply if not properly handled during disposal. This could be avoided if the panels are recycled, but the technology is currently not as widely available as it needs to be. The use of rare metals like those found in CIGS, CdTe, and GaAs can also be an expensive and potentially limiting factor in producing large amounts of thin-film solar cells.
Other Types
The variety of solar panels is much greater than what is currently on the commercial market. Many newer types of solar technology are in development, and older types are being studied for possible increases in efficiency and decreases in cost. Several of these emerging technologies are in the pilot phase of testing, while others remain proven only in laboratory settings. Here are some of the other types of solar panels that have been developed.
Bifacial Solar Panels
Traditional solar panels only have solar cells on one side of the panel. Bifacial solar panels have solar cells built on both sides in order to allow them to collect not only incoming sunlight, but also albedo, or reflected light off the ground beneath them. They also move with the sun in order to maximize the amount of time that sunlight can be collected on either side of the panel. A study from the National Renewable Energy Laboratory showed a 9% increase in efficiency over single-sided panels.
Concentrator Photovoltaic Technology
Concentrator photovoltaic technology (CPV) uses optical equipment and techniques such as curved mirrors to concentrate solar energy in a cost-efficient way. Because these panels concentrate sunlight, they do not need as many solar cells to produce an equal amount of electricity. This means that these solar panels can use higher quality solar cells at a lower overall cost.
Organic Photovoltaics
Organic photovoltaic cells use small organic molecules or layers of organic polymers to conduct electricity. These cells are lightweight, flexible, and have a lower overall cost and environmental impact than many other types of solar cells.
Perovskite Cells
The Perovskite crystalline structure of the light-collecting material gives these cells their name. They are low cost, easy to manufacture, and have a high absorbance. They are currently too unstable for large-scale use.
Dye-Sensitized Solar Cells (DSSC)
These five-layered thin-film cells use a special sensitizing dye to help the flow of electrons which creates the current to produce electricity. DSSC have the advantage of working in low light conditions and increasing efficiency as temperatures rise, but some of the chemicals they contain will freeze at low temperatures, which makes the unit inoperable in such situations.
Quantum Dots
This technology has only been tested in laboratories, but it has shown several positive attributes. Quantum dot cells are made from different metals and work on the nano-scale, so their power production-to-weight ratio is very good. Unfortunately, they can also be highly toxic to people and the environment if not handled and disposed of properly.
Almost all solar panels sold commercially are monocrystalline, common because they’re so compact, efficient, and long-lasting. Monocrystalline solar panels are also proven to be more durable under high temperatures.
Monocrystalline solar panels are the most efficient, with ratings ranging from 17% to 25%. In general, the more aligned the silicon molecules of a solar panel are, the better the panel will be at converting solar energy. The monocrystalline variety has the most aligned molecules because it’s cut from a single source of silicon.
Thin-film solar panels tend to be the cheapest of the three commercially available options. This is because they’re easier to manufacture and require less materials. However, they also tend to be the least efficient.
Some may choose to buy polycrystalline solar panels because they’re cheaper than monocrystalline panels and less wasteful. They’re less efficient and bigger than their more common counterparts, but you might get more bang for your buck if you have abundant space and access to sunshine.
Thin-film solar panels are lightweight and flexible, so they can better adapt to unconventional building situations. They’re also much cheaper than other types of solar panels and less wasteful because they use less silicon.
- Luceño-Sánchez, José Antonio, et al. Materials for Photovoltaics: State of Art and Recent Developments. International Journal of Molecular Sciences, vol. 20, no. 4, 2019, pp. 976., doi:10.3390/ijms20040976
- Solar Photovoltaic Cell Basics. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.
- Qazi, Salahuddin. Standalone Photovoltaic (PV) Systems for Disaster Relief and Remote Areas. Elsevier, 2017., doi:10.1016/C2014-0-03107-3
- Bayod-Rújula, Angel Antonio. Chapter 8—Solar Photovoltaics (PV). Solar Hydrogen Production: Processes, Systems and Technologies, 2019, pp. 237-295., doi:10.1016/B978-0-12-814853-2.00008-4
- Taraba, Michal. Properties Measurement of the Thin Film Solar Panels Under Adverse Weather Conditions. Transportation Research Procedia, vol. 40, 2019, pp. 535-540., doi:10.1016/j.trpro.2019.07.077
- Bagher, Askari Muhammed, et al. Types of Solar Cells and Applications. American Journal of Optics and Photonics, vol. 3, no. 5, 2015, pp. 94-113., doi:10.11648/j.ajop.20150305.17
- Project Profile: Performance Models and Standards for Bifacial PV Module Technologies. U.S. Department of Energy.
- Bifacial Solar Advances With the Times—and the Sun. National Renewable Energy Laboratory.
- Current Status of Concentrator Photovoltaic (CPV) Technology. National Renewable Energy Laboratory.
Types of Solar Panels
All solar panels are not the same. They differ in performance, appearance, price, material, application, and size. The types of solar panels you need for your home or office depends on the roof size, consumption, budget, efficiency, among other factors.
There are 3 common kinds of solar panels:
- Monocrystalline solar panels
- Polycrystalline solar panels
- Thin-film solar panels
Although there are other types of solar panels, most are not economically or technologically viable.
The types of solar panels are classified into 3 groups. The classification is based on the kind of materials used and the commercialization of the product.
- First-generation solar panels
- Second-generation solar panels
- Third-generation solar panels
First Generation Solar Panels
Monocrystalline and polycrystalline solar panels fall under this category. The cells are made of crystalline silicon and gallium arsenide (GaAs) wafers. They are the most common types of solar panels in commercial and residential solar panel installation. Because of their widespread use, they are also referred to as conventional or traditional solar panels.
First-generation solar panels are the oldest PV cells, and their fabrication and technological applications are well-known. GaAs is a better material than silicon because it has higher optical properties. Therefore, it requires thicker silicon wafers to harness the same amount of energy as GaAs.
But, gallium and arsenide are expensive and not commercially viable for the manufacture of solar panels. The materials are limited on the surface of the earth. Therefore, silicon remains the primary material in the manufacture of solar panels.
Let’s have a look at each of the solar panel types under the first generation.
Monocrystalline Solar Panels
The solar cells are made of the purest form of silicon. They have a uniform silicon composition, which gives them high efficiency. They have rounded edges because silicon crystals are cylindrical. You can identify the panels from the even rows and columns.
The silicon wafers used in monocrystalline cells have high efficiency (up to 20%) compared to other types of solar panels. Therefore, you require fewer monocrystalline solar panels; this makes them ideal for use in small-sized roofs. You can also use this type in pole mounts because the space is also limited.
However, the price of monocrystalline solar panels is higher. They are more costly to manufacture than the other types. The solar panels have a longer lifespan because of increased resistance to temperatures; thus, a more extended warranty. The monocrystalline solar panel system could last for more than 30 years.
Polycrystalline Solar Panels
Do you want to install cheap solar panels, and you have unlimited roof space? Polycrystalline solar cells have lower efficiency but are feasible for residential buildings where space may not be a problem. The panels are also referred to as multi-crystalline solar panels.
Although they are made from the same material as monocrystalline, they have lower efficiency, ranging between 15-17%. The solar panels have a speckled bluish color, which many homeowners consider unattractive. Another difference from the former type is the appearance. Polycrystalline solar panels have sharp wafer edges because of how they are manufactured.
A decade ago, polycrystalline solar panels were the most common type of solar panels. However, their popularity has dwindled because of low efficiency. The average capacity of an average polycrystalline solar panel system is approximately 300 watts. Therefore, you require around 20 for a 6 kW solar panel system.
The life expectancy of polycrystalline solar panels is lower. Thus, a shorter warranty period than monocrystalline solar panels. The choice between polycrystalline and monocrystalline solar panels is not outright. Each has its ideal application, depending on your situation. You should go for multi-crystalline solar panels if you want to cut on cost and the size of your roof or ground mounts is not limited. However, the panels are affected by high temperatures, which can lower their lifespan.
Second Generation Solar Panels
Thin-film solar panels make up the second generation of solar panels. some of the most common types of 2 nd generation solar cells include:
- Amorphous silicon solar panels
- Cadmium telluride (CdTe)
- Copper indium gallium selenide (CIGS)
- Concentrated photovoltaic cells (CVP)
Thin-film solar panels have lower efficiency than the crystalline types because of the material used. They are common in utility-scale applications where space is plenty.
Amorphous Silicon
Amorphous silicon (a-Si) solar panels are made of hydrogenated silicon, which has low energy conversion efficiency. The material is deposited in flexible substrates like metal, plastic, and glass. The solar panels are less durable compared to crystalline silicon cells; thus, a shorter warranty period.
Cadmium telluride
CdTe solar panels are made from semi-conductors pressed between thin films of glass. There are concerns about cadmium safety, but studies show that a compound of the two elements has lower toxicity than Cd alone. Therefore, proper disposal of the material is advisable to prevent any adverse health effects. This type of solar panel is the most common in commercial thin-film applications.
Copper indium gallium selenide
CIGS solar panels are an exciting option because of their high efficiency. However, the cost of manufacturing solar cells makes them an expensive option. It is difficult for copper indium gallium selenide solar panels to compete with crystalline silicon cells. However, the solar panels have a higher efficiency than other kinds.
Thin-film solar panels are the most flexible. They can adopt different shapes for aesthetic value. There are many studies to improve solar panels’ efficiency and overcome the commercial and technological barriers of the solar cells.
Concentrated photovoltaic cells
CPV is a new technology that uses curved mirrors and lenses to concentrate sunlight to highly efficient solar cells. The solar panels can achieve an efficiency of up to 41%, which is double what the second most efficient type can harness. The technology’s commercial application will be a significant breakthrough in solar energy because it will reduce the cost and space required to install solar panels.
Third Generation Solar Panels
There is a limit to the efficiency of solar panels. Shockley-Queisser ranges between 31-41% for a single bandgap solar cell. The third-generation of solar panels seeks to overcome this limit and improve efficiency. The main objective of the technology is to convert solar cell non-compatible light frequencies to compatible frequencies.
There are promising products under development that could make solar energy more efficient. The solar panels seek to tap into the strengths of crystalline silicon and the 2nd generation PV technology. The most advanced third-generation solar panels include:
Which Type of Solar Panels Should I Buy?
There is no direct answer to this question without an evaluation of your situation. Some of the essential factors that affect the type of solar panels for your commercial or residential installation include:
- Size of the roof or ground mounting space.
- Budget.
- Aesthetic preferences.
- Size of the solar panel system.
Monocrystalline solar panels are the most ideal if you have limited space. On the other hand, polycrystalline cells are suitable when low on the budget. Thin-film solar cells are the most common in power purchase agreements because of the short lifespan. They are also ideal for utility-scale or communal solar energy installations.
Solar energy technology undergoes drastic changes in a short period because it is a developing technology. There are many feasibility studies to evaluate the application of different solar panels under review. Therefore, what is efficient today might be outdated within a year. You should keep an eye on the industry and do thorough research before settling for any solar panels.