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High-Efficiency Silicon Inverted Pyramid-Based Passivated Emitter and Rear Cells. Perl solar cell

High-Efficiency Silicon Inverted Pyramid-Based Passivated Emitter and Rear Cells. Perl solar cell

    Perl solar cell

    Anyone who follows the latest developments in the Solar Photovoltaic market will have come across the technical term PERC at least once in the past year or so. All respectable suppliers compete to launch the best PERC as a means to secure the premium part of the market share.

    PERC stands for Passivated Emitter Rear Cell; the concept was first proposed by the University of New South Wales in a grant report in 1984 (1). As a matter of fact, the modern PERC generally refers to two specific configurations called PERT (Passivated Emitter, Rear Totally-diffused), and PERL (Passivated Emitter, Rear Locally-doped), which have proven to be the most viable solutions amongst other PERC configurations (2).

    The PERC concept has taken some time to meet with commercial success, with the first high efficiency solar cells being fabricated in a lab with up to 20% efficiency from the 1990s onwards (3). Obviously at the time, there were other competing technologies, e.g. back contact and HIT. Hence, the PERC concept was only one of many promising ideas to increase solar cell efficiency. It took nearly 30 years for the industry to catch up with the concept and produce efficiencies achieved at the research level.

    How does a PERC Solar Cell work?

    In a nutshell, a PERC solar cell can be created by adding a rear surface passivation film to a conventional crystalline cell. In practice, it involves two additional steps: first, a rear passivation film is applied. Then, either lasers or chemicals are used to open up tiny s in the film through which the rear conducting layer can contact the silicon below the passivation layer. Figure 1 compares the configurations of conventional and PERC solar cells.

    Figure 1: Comparison of cell configurations

    The above technique enables the efficiency of the solar cell to be improved in three ways:

    By minimising surface recombination

    The atoms at the surface of a silicon wafer have ‘dangling bonds’ which can capture charge carrying electrons and pull them back into the silicon crystal structure (a process called surface recombination). As a result, when an electron reaches the back surface of a conventional solar cell, it is likely to be captured and does not contribute to the current. However in a PERC solar cell, a passivated film is grown on the back surface of the solar cell and reduces this effect by tying up the ‘dangling bonds’. A charge carrying electron that strays too close to the back surface is allowed to continue on its way and the chance it will reach the emitter and contribute to the electric current produced by the solar cell is increased. (Figure 2).

    Figure 2. How a PERC cell increases efficiency by decreasing surface recombination.

    Longer wavelengths (red light) generate electrons near the back surface, compared to shorter wavelengths (blue light) (4). Since the PERC solar cell helps prevent surface recombination, it will still be able to capture these wavelengths (5). This capability increases the solar cell performance during mornings and evenings when longer wavelengths are present, which leads to the claims of better weak light performance by many manufacturers.

    By Increasing Internal Reflectivity to Capture Light

    The rear film reflects the light that passes through the solar cell without being absorbed. This provides the light with more opportunity for a second absorption attempt (see Figure 3). In other words, the efficiency of energy conversion is just becoming higher.

    Figure 3 PERC cell increases efficiency by reflecting light back through the solar cell

    By Reflecting Counter-productive Wavelengths

    Generally, silicon solar cells stop absorbing wavelengths above 1180 nm, instead they are absorbed by the backside metallisation layer and tuned into heat (4). The rear passivated film reflects these counter-productive wavelengths out of the solar cell and hence maintains cooler temperatures. As a result, PERC solar cells are considered to have better heat resistance.

    All of the above, if manufactured correctly, will undoubtedly increase the solar cell efficiency. The current commercially available PERC solar cells are in excess of 20% with a record efficiency of nearly 23%. As this technology is piggybacked on conventional silicon solar cells, you can bet the efficiency will not stop here and will keep on improving!

    Why has it become the most exciting feature amongst the new PV technologies?

    It has been a holy grail in the PV industry to find a product with the highest possible efficiency, while maintaining the low manufacturing cost. To some extent, PERC solar cells provide the answer. Hence, it is not surprising that this technology has a rosy outlook.

    From standstill, the PERC commercial production capacity is expected to occupy nearly half of the total solar PV cell capacity by 2020 (see Figure 4) (6).

    Figure 4: Global production capacity for PV cells from 2016 to 2020 (Source: Energy Trend)

    The main attraction is that the PERC production requires minimum modifications to existing solar cell manufacturing lines. The existing lines can easily be upgraded to produce PERC solar cells without having to invest in large capital expenditures or completely overhaul the entire lines. In other words, one could increase the solar cell efficiency without having to take huge financial risks. Meanwhile, by recycling most of the existing equipment, one simply makes the money work harder for the original investment. It appears to be a no brainer.

    Too good to be true?

    Despite the PERC being a thirty year old concept, they have not been tested commercially until quite recently. It was first reported by Ramspeck (7) that PERC cells can exhibit stronger power degradations during the early days through a process called light-induced degradation (LID).

    Fraunhofer Centre for Silicon Photovoltaics in Germany subsequently conducted extensive research to find out the degradation mechanism due to illumination (8). They were mainly attributed to chemical and physical root causes, namely Boron-oxygen complex activation and Iron-boron pair dissociation for the former, and elevated temperature for the latter.

    To be fair, LID is not a new phenomenon, affecting conventional solar cells too. This type of degradation has simply entered the spotlight with the introduction of mass-produced PERC solar cells.

    In response, some cell manufacturers have addressed the issue by adopting small changes to the solar cell process, such as modified process temperatures and different wafer materials (9).


    PERC is going to take centre stage in the foreseeable future. This technology will progressively take a bigger market share – the benefits to developers, designers and installers are obvious.

    Sooner or later, most of the PV modules will feature this technology. One just has to carefully choose trusted, quality suppliers with proven test records.

    This fuss is, after all, worth paying attention to.


    M.A. Green, A.W. Blakers, J. Kurianski, S. Narayanan, J. Shi, T. Szpitalak, M. Taouk, S.R. Wenham and M.R. Willison, Ultimate Performance Silicon Solar Cells, Final Report, NERDDP Project 81/1264, Jan. 82-Dec. 83 (dated Feb., 1984).

    M.A. Green, The Passivated Emitter and Rear Cell (PERC): From conception to mass production, Solar Energy Materials Solar Cells, 143 (2015) 190-197.

    C.J. Chiangand, E.H. Richards, A 20% efficient photovoltaic concentrator module, conferencerecord,21st IEEE Photovoltaic Specialists Conference, Kissimmee, May 1990, pp.861–863.

    D. de Rooij, PPERC solar cell technology: why will PERC dominate silicon cell technology? 2015 (

    PERC cells: production costs down, efficiency up. May 2016. (

    TrendForce Reports PERC Cell’s Global Production Capacity to Reach 25GW in 2017, Resulting in Doubling of Total Annual Output. 19/1/2017 (

    Ramspeck, K. et al. 2012, “Light induced degradation of rear passivated mc-Si cells”, Proc. 27th EU PVSEC, Frankfurt, Germany, pp. 861–865.

    Tabea Luka, Christian Hagendorf Marko Turek, Multicrystalline PERC solar cells: Is light-induced degradation challenging the efficiency gain of rear passivation? Photovoltaics International, 2016

    Haase, J. Mono as well as multi PERC cells will get a significant market share, PV Magazine 10/2015, pp.74.77.

    high-efficiency, silicon, inverted, pyramid-based, passivated

    High-Efficiency Silicon Inverted Pyramid-Based Passivated Emitter and Rear Cells

    Surface texturing is one of the most important techniques for improving the performance of photovoltaic (PV) device. As an appealing front texture, inverted pyramid (IP) has attracted lots of research interests due to its superior antireflection effect and structural characteristics. In this paper, we prepare high-uniform silicon (Si) IPs structures on a commercial monocrystalline silicon wafer with a standard size of 156 × 156 mm 2 employing the metal-assisted chemical etching (MACE) and alkali anisotropic etching technique. Combining the front IPs textures with the rear surface passivation of Al2O3/SiNx, we fabricate a novel Si IP-based passivated emitter and rear cell (PERC). Benefiting from the optical superiority of the optimized IPs and the improvement of electrical performance of the device, we achieve a high efficiency of 21.4% of the Si IP-based PERC, which is comparable with the average efficiency of the commercial PERC solar cells. The optimizing morphology of IP textures is the key to the improvement of the short circuit current Isc from 9.51 A to 9.63 A; meanwhile, simultaneous stack SiO2/SiNx passivation for the Si IP-based n emitter and stack Al2O3/SiNx passivation for rear surface guarantees a high open-circuit voltage Voc of 0.677 V. The achievement of this high-performance PV device demonstrates a competitive texturing technique and a promising prospect for the mass production of the Si IP-based PERC.


    Improving efficiency is the eternal theme of the solar cell industry, which mainly focuses on two aspects: the optical performance and electrical performance. The front texturing technique is of importance for prompting the optical performance of the device. Inverted pyramid (IP) as an attractive light-trapping structure has attracted considerable attention due to its superior antireflection effect and structural characteristics [1,2,3,4,5,6,7]. To be specific, the incoming short-wavelength light in silicon (Si) IP undergoes triple or more bounces before being reflected away, possessing one or more bounces than that in traditional upright pyramids [7,8,9]. Meanwhile, this inverted pyramid-structured Si will avoid severe recombination losses faced by the nanostructured black Si [10,11,12,13,14,15,16] because of its big and open structural characteristic.

    By employing the lithography inverted pyramid textures on the front surface and SiO2 passivation of the rear surface, Green’s group [17] has successfully fabricated a 25.0% efficient passivated emitter and rear local-diffused solar cell (PERL) with an area of 4 cm 2. However, the lithography technique is not suitable for mass production because of its expense, low production-capacity, and incompatibility. Recently, many research interests turn to the metal-assisted chemical etching (MACE) large-area inverted pyramids since the MACE technique is simple, low-cost, large-area, and compatible with the current production line [14, 18,19,20,21]. For example, Jiang et al. [7] have reported inverted-pyramids nanostructure prepared by the MACE process followed by a post nanostructure rebuilding solution treatment and the conversion efficiency of IPs based multi-crystalline silicon (mc-Si) solar cells in large size of 156 × 156 mm 2 wafers reached up to 18.62%. By utilizing Cu nanoparticles to catalyze chemical etching of Si, Yang et al. [8] have achieved 18.87% efficient IP-structured Si solar cells with a large area. Zhang et al. [9] have fabricated sc-Si solar cell with IP microstructure by modulated alkaline texturing combined with an optimized MACE method and have achieved a 20.19% efficient 1-μm-sized IP-textured device with a large area. So far, the performances of Si IP solar cell with a large area are not yet satisfied suffering from the large-area uniformity of IP morphology, the control of the IP feature size, and the passivation of the device. As a result, the front-optimized Si IP textures together with the rear passivation are expected to improve cell performance further.

    In this paper, we successfully fabricated 21.4% efficiency Si IP-based passivated emitter and rear cells (PERC) with a standard solar wafer size of 156 × 156 mm 2 by combining the front optimized MACE IP textures with the simultaneous stack SiO2/SiNx passivation for the Si IP-based n emitter and stack Al2O3/SiNx passivation for the rear surface. The key to high performance lies in the optical superiority of the IP textures and the reduced electrical losses by the simultaneous passivation of Si IP-based n emitter and rear surface. This novel Si IP-based PERC device structure and technique show a great potential in mass production of high-efficiency silicon-based solar cell.


    The device structure of Si IP-based PERC is designed as follows: (i) The Si IP-based PERC n emitter is passivated by stack SiO2/SiNx (PECVD) layers as shown in Fig. 1a. The Si IP structures have a good short-wavelength antireflection effect due to more opportunities of three or more bounces; meanwhile, the stack SiO2/SiNx layer provides a further reduced reflectance and an excellent passivation effect for the Si IPs n emitter. (ii) The rear reflector is composed of stack Al2O3 (ALD)/SiNx (PECVD) layers and screen-printed Al as shown in Fig. 1a. Stack dielectric layers are designed to optimize the optical properties of long-wavelength by increasing inner rear reflectance while maintaining a good electrical passivation effect, which is attributed to the field- effect passivation of the fixed negative charges in Al2O3 layer and the chemical passivation of hydrogen atoms in SiNx film. In a word, both optical and electrical properties in this design are simultaneously considered to ensure a high performance of Si IP-based PERC.

    Commercial 180-μm-thick 156 mm × 156 mm (100)-oriented crystalline silicon (c-Si), boron-doped (1–3 Ω·cm) p-type wafers were used as substrates. After the standard cleaning process, inverted pyramid textures were prepared on the surface of Si wafers as follows: (1) The cleaned Si wafers were immersed in the mixed solutions of AgNO3(0.0001 M)/HF (4 M)/H2O2 (1 M) for 300 s, resulting in porous Si. (2) Si wafers with porous Si were etched in an NH4OH:H2O2:H2O = 1:1:6 (volume) solutions for 200 s to remove the residual Ag nanoparticles. (3) The wafers with porous Si were modified in an HNO3:H2O:HF = 4:2:1 (volume) solution to prepare nanoholes. (4) Inverted-pyramids textures were fabricated on the surface of Si wafer by anisotropic etching of 60 °C-NaOH solutions for 30, 60, and 90 s, respectively.

    POCl3 diffuses for 40 min at 800 °C in the quartz tube furnace and then n emitter forms on the front of the wafer (M5111-4WL/UM, CETC 48th Research Institute). The sheet resistance of Si IP-based n emitter is 105-110 Ω·sq −1. The selective emitter was fabricated on the front surface of the wafer by laser doping (DR-SE-DY70, DR Laser). After the rear surface polished, SiO2 passivation films were prepared by thermal oxidation on the front of silicon wafers. The Al2O3 passivation layers were deposited on the rear surface of wafer by ALD (PEALD-156, HUGUANG Scientific Instruments of Beijing) for ≈ 30 min at 150 °C. The PECVD-SiNx layers were formed by the reaction of NH4/SiH4 (SC-TD-450C). Subsequently, the rear stack passivation layers of Si IP-based wafer were locally ablated by a 532-nm wavelength and 10-ps pulse length laser (DR-AL-Y60, DR Laser), in order to form the 50-μm width and 1-mm pitch local line openings. Finally, the Si IP-based PERC underwent the commercial screen-printing (PV1200, DEK) and co-firing process (CF-Series, Despatch), to form well Ohmic contacts and local BSFs.

    The morphologies and structures of the samples were characterized with a JEOL JSM-6390LA scanning electron microscope. The lifetime of the minority carriers was measured by using a Sinton WCT-120. The absorption spectra were determined by FTIR (Tensor 27, BRUKER). The C-V curve is measured by an impedance analyzer (E4900A, KEYSIGHT). The photoluminescence and electroluminescence photos were taken by PL/EL imaging analysis system (LIS-R2, BTimaging). The reflectance spectra, as well as the IQEs and EQEs, were measured on the platform of quantum efficiency measurement (QEX10, PV Measurements). The electrical parameters of the solar cells were investigated by current-voltage (I–V) measurement under the illumination of AM1.5 (Crown Tech IVTest Station 2000). The cell efficiency was measured by using a BERGER Lichttechnik Single Cell Tester.

    Results and Discussion

    Figure 2a–e shows the top-view SEM images of the different process steps for the silicon surface texturing. Figure 2a shows the 50–80 nm porous Si on the surface of Si wafer etched by MACE method in the mixed solutions of AgNO3/HF/H2O2. Subsequently, the porous Si is modified by the isotropic etching in the mixed aqueous solutions containing HF/HNO3 and turns to be nanohole structures with a diameter of 800 nm as shown in Fig. 2b. Finally, the micron inverted pyramids (IPs) with different sizes (Fig. 2c–e) are obtained by sodium hydroxide in aqueous solution at 60 °C for 30, 60, and 90 s, respectively. From Fig. 2c–e, we can see that after alkali treatment, the IPs structure sizes for three etching time of 30, 60, and 90 s are ~ 1, 1.3, and 1.8 μm, respectively, meaning an increasing size of IP with the increase of alkali treatment time. Also, we notice that the IPs tend to collapse and transit to be the upright pyramids with the increase of the etching time. As known, the inverted pyramids have the advantage of light trapping over upright ones because light will undergo extra one or two bounces in inverted pyramids than that in upright pyramids. Therefore, the structures with shorter etching time are suitable for the light-trapping textures of PV devices because of the advantage in the short-wavelength antireflection. Figure 2f is the compared photos for different surface structures corresponding to Fig. 2a–e.

    Now we turn to the optical properties of Si IP-strus. From the reflectance over the whole wavelength range of 300–1100 nm (Fig. 3a), we observe that the porous Si has a low reflection because of the excellent light-trapping performance of nanostructures [22,23,24]. For nanohole structures, the reflectance in the whole wavelength range has an obvious increase, which is attributed to the decrease of density and increase of feature size of nanoholes. After NaOH treatment for 30 s, benefiting from 3–4 bounces between the (111) planes of the IP, the IPs structures display lower reflection over the 300–1100 nm wavelength range, especially in the short-wavelength range of 300–500 nm. With the alkali etching time increasing, the IPs become larger and tend to be the upright pyramids, resulting in an increasing reflectance. When all samples were covered with the same stack SiO2/SiNx coating, the reflectance drop sharply by more than 10%, which is attributed to the combined reflectance from the optical interference of the stack SiO2/SiNx thin films and the surface structures. In this case, the reflection spectra of samples from different processes are mainly different in the wavelength range of 300–600 nm, which is caused by the difference of feature size of IPs. In particular, Si IP-strus covered by the stack SiO2/SiNx layers displays better short-wavelength antireflection ability than the others, indicating the excellent external quantum efficiencies (EQEs) in the short-wavelength range.

    Furthermore, we calculate the average solar reflectivity Rave (see Fig. 3b) over the wavelength range of 300–1100 nm and compare the reflectivity of Si IP-strus with other structures corresponding to different intermediate processes shown in Fig. 2a–c. Rave can be calculated by the expression of

    where R(λ) and S(λ) denote the measured reflectance and AM1.5 solar photon spectral distribution, respectively. As shown in Fig. 3b, the Raves of porous Si, nanoholes, IPs, and IPs with SiO2/SiNx coating are 8.22, 17.96, 15.18 (group 1—30 s)/17.35% (group 2—60 s)/20.3% (group 3—90 s), and 3.91% (group 1—30 s)/4.48% (group 2—60 s)/5.60% (group 3—90 s), respectively. The Raves show that the IP-strus have a better antireflection ability than nanoholes and show a decreasing trend with the increase of feature size. When IP-Strus are coated by the stack SiO2/SiNx layers, the lowest Rave is 3.91%, revealing an ideal light-trapping structure for the PV device.

    The stack SiO2 (~ 2 nm)/SiNx (~ 75 nm) passivation for the Si IP-based n emitter is an effective way for achieving well electrical performance of IP-based PERC and their passivation effect [1] and mechanism have been systematically studied in our previous work [14]. To show the electrical superiority of the stack Al2O3/SiNx passivation layers at the rear of our device, we investigate the influence of the different annealing and light-soaking conditions on the effective minority carrier lifetime (τeff) with respect to the injection level (Δn), as shown in Fig. 4a. Notice that the polished Si wafers have the bulk minority carrier lifetime of ~ 350 μs, and the stack Al2O3/SiNx layers are symmetrically deposited on both sides of polished Si wafers. The thickness of inner Al2O3 and the outer SiNx layer is estimated as ~ 3 and ~ 125 nm, respectively. Two annealing conditions are performed in the air atmosphere: 300 °C and 800 °C for 15 min. Then the wafers are illuminated at 25 °C under the full-wave ranged halogen lamp with a power intensity of 50 mW cm −2 for 100 s. As can be seen from Fig. 4a, the 48 μs τeff (300 °C) and 126 μs τeff (800 °C) after annealing are much higher than the 22 μs τeff of the as-deposited Al2O3/SiNx passivated samples at the injection level of 1.2 × 10 15 cm −3.

    Importantly, the effective minority lifetime of annealed samples after 100 s of illumination are 230 μs and 150 μs, respectively, much higher than 126 μs and 48 μs before illumination, demonstrating a very clear light-enhanced c-Si surface passivation of Al2O3/SiNx layers. The charge trapping effect during light soaking [25,26,27,28] could be one of the main mechanisms for the light-enhanced c-Si surface passivation of Al2O3/SiNx films. As Al2O3 films are reported to have a negative fixed charge density [29,30,31,32], some of the excess electrons generated by light were likely to be injected or tunneled into trap states in the inner Al2O3 film, resulting in an increased level of field-effect passivation. Interestingly, the light-enhanced passivation effect at 300 °C annealing is better than that at 800 °C, meaning that light-soaking at a lower temperature annealing is a more effective way to the application of PV device.

    To study the effect of the annealing process on the surface modification, we compare the Fourier transform infrared spectroscopic (FTIR) absorption spectra of the annealed samples with that of the as-deposition sample. Figure 4b manifests that the Si–N, Si–O, Si–H, and N–H bonds correspond to the stretching absorption peaks at the wavenumbers of ~ 840, 1070, 2200, and 3340 cm −1. respectively. We see that the densities of both the Si–N and Si–O bonds show an obvious increase after annealing; meanwhile, the density of the Si–H bonds increases slightly. The increases of the Si–O and Si–H bond density implies the decrease of the dangling bonds at the interface of Si/SiO2, resulting in a better passivation effect [33]. Also, the annealing process promotes the density of Si–N bonds, indicating a more dense structure which can effectively prevent the out diffusion of H from entering into the environment instead of into Si bulk. However, for excessively high annealing temperature, the H in Si–H and N–H groups can escape from the bulk Si and the dielectric layers to the environment, which causes the decline of the passivation effect. The result of FTIR is consistent with that of the effective minority lifetime.

    To further understand the difference of passivation mechanism between thermal annealing and light-soaking treatment, we analysis the density of fixed charges (Nf) and the density of interface traps (Nit) at the interface of Si and Al2O3 (ALD)/SiNx (PECVD) stack layers by using capacitance–voltage (C-V) measurements from a rigorous metal–oxide– semiconductor (MOS) model.

    Nf can be obtained from the following equation:

    where the following expression can calculate VFB

    How Do Solar Cells Work?

    Whether you’re choosing a solar panel for rooftops or remote areas, it helps to have a basic knowledge of the different types of solar cell modules, as well as the benefits and drawbacks of each. However, before anything, it helps to also brush up on the science that goes on behind their sun-powered solar technology, the photovoltaic cells.

    So, how do solar panels work? UnboundSolar is here to break it all down and explore the science behind photovoltaic solar cells that make up our solar panels – and in easy-to-grasp basic terms. Ready? Let’s begin.

    First, What Are Solar Cells?

    In basic terms, a solar cell captures the sun’s energy and transforms it into electrical power. To add, many solar cells are made from silicon, a chemical element found in sand. Solar cells, which are octagonally shaped and lend a bluish hue, are usually arranged to create larger solar modules, which are then made into what we know as solar panel units that rest on our homes, businesses or other remote locations. Solar cells can also be added to smaller solar-powered handheld products like a phone charger or outdoor landscape lighting.

    How Do Solar Cells Work?

    Okay, now that you know what solar cells are, on to the real question: how do solar cells work? Actually, it’s very similar to a battery. But unlike a battery that derives its electricity from chemicals, solar panel cells use the sun’s energy by capturing sunlight. This sunlight is made of photons, super-tiny particles inside beams of sunlight, which are plentiful, to say the least. Our earth will never run out of photons, unlike other unsustainable energy resources like gas or oil.

    So, the solar cells capture the photons, but what comes next? How does a solar cell transform these photons into energy (or electrons) that we use on a daily basis?

    To start, first you need to know that each solar cell is capable of generating a handful of volts (depending on the type). This is why we have to arrange larger solar cell modules into solar panels. Plus, you need to understand how solar panels create electricity.

    When the sun’s energy, or photons, reach the solar cell, its atoms basically shake off electrons. Photovoltaic solar panels feature a semiconductor along the positive (P-type silicon) and negative (N-type silicon) layer of a solar cell, and when the shed electrons reach the inverter, converting direct current (DC) into alternating current (AC), it can then transform the electrons into an electric current, very much the same way a battery does. Solar cell systems also capture the energy and store it in a solar battery for continuous use, even when the sun isn’t shining.

    Through this electrical circuit, you can run anything with electrical power within the home or wherever you need. If you have multiple solar panel modules joined and wired together, it creates a solar array. panels = more energy. Voila!

    How Do Solar Cells Work in Bad Weather?

    So, clearly, solar cells work best on a clear, sunny day. But how do solar cells work when the weather takes a turn for the worse or is simply overcast? And does temperature play a role? It’s no mystery that weather conditions can have a negative impact on solar energy systems, but let’s explore this a bit more.

    Ideally, you want a sunny day to produce tons of solar energy. But it’s worth noting that solar panels are not entirely efficient in the dead heat of summer. On the contrary, solar panels are more efficient on a sunny winter day. Why? Since solar panels are essentially an electronic, they will generate less voltage and electricity as the day warms and temperatures rise. However, just because solar panels work more efficiently in cooler temps, doesn’t mean they produce more electricity. Clouds can put a damper on things too and summertime means the sun is out far longer and there are also fewer clouds. Ultimately, while solar panels are more efficient in cooler weather, a sunnier summer day will generate more electricity.

    Of course, we can’t talk about the weather without talking about regional climates. Certain regions like the South or California will always get more sunny days that chase the clouds away. So the general assumption is that certain regions of the U.S. and specific states (the Pacific Northwest, Seattle and Oregon, for example) are not-so-great candidates for solar power. However, bad weather is not really the factor.

    In short: Solar panels can still gather electricity on a cloudy day (the same way we can get a sunburn from solar radiation), but it takes the right high-quality solar panels to get the job done. We will talk more on that next.

    Different Types of Solar Cells and Solar Panels

    Now that you understand how solar cells work, let’s talk about the different types of solar cell technology and solar panels. There are three different photovoltaic technologies: monocrystalline (also known as single crystal silicon), polycrystalline and thin film. Below, we dive into each one to help you better understand which solar panel style is best suited for your residence or business.

    Crystalline Silicon Solar Cells

    Out of the three types of solar cells, there are two crystalline silicon versions: monocrystalline and polycrystalline. These are the most common photovoltaic solar technology out there and often what comes to mind when you think of solar panels.

    Monocrystalline (Single Crystal) Solar Cells

    Invented in 1955, monocrystalline solar cells were the first photovoltaic solar technology. Cut from a single source of dark blue silicon crystal, as opposed to a blend like polycrystalline, monocrystalline solar cells are more durable though both are equally reliable. Monocrystalline solar cells are sliced into fully rounded wafer-like shapes (sometimes trimmed), minimizing waste and maintaining their circle shape to optimize the sun efficiently. Generally speaking, monocrystalline solar cells are more efficient solar cells, with the exception of mono-PERCs, which we’ll dive into later.

    Polycrystalline Solar Cells

    Polycrystalline solar cells are made from the same silicone material. However, unlike monocrystalline that are sliced into round disk-like shapes, polycrystalline solar cells are made from melted silicon, which is then poured into a square block mold that is cut into square wafers. Once the melted polycrystalline silicon cools, it crystallizes and gives off a variegated blue gemstone effect. Polycrystalline solar cells do have a lower efficiency than monocrystalline.

    The polycrystalline manufacturing process can vary too. Today, you can find polycrystalline solar panels with growths of ribbon and crystalline film on glass. As a whole, crystalline silicon modules are extremely durable and offer long warranties (many offer 25-year warranties). When comparing monocrystalline and polycrystalline solar panels, keep in mind that mono are often smaller in size per watt of power output and polycrystalline is more affordable (albeit slightly).

    But Wait, What Are PERC Solar Cells?

    When exploring monocrystalline solar cells, you might find ones called mono PERC cells. So what is the difference? In basic terms, a mono-PERC solar panel is a more efficient version of monocrystalline.

    The Passivated Emitter and Rear Cell (PERC) is an extra passivated layer that is added to the back of the solar cell, which helps to reflect the sun’s rays back into the solar cell module, giving it an extra boost. PERL solar cells come in handy, especially when it’s needed most, like in low-light conditions or when there is limited mounting space.

    Luckily, this passivated layer can be attached to both monocrystalline and polycrystalline solar cells as a simple modification and made with the same solar panel equipment (although monocrystalline is much more common and efficient). As an easy modification, PERC solar cells can be added to create better efficiency.

    Thin-Film Solar Cells (Amorphous)

    Aside from crystalline solar cells, there are thin-film solar cells. Unlike the disc-like wafer mono and poly solar cells, thin-film solar cells are photovoltaic cells that are made of a super thin silicon or sometimes cadmium telluride. This microscopic layer minimizes the use of silicon, incorporating other solar technology that makes thin-film solar cells more sustainable. This super-thin silicon layer of solar cells can be applied to metal and glass panels, which eliminates the sliced wafer manufacturing process and the need to be assembled.

    How can thin-film solar cells be used? By using this plastic glazing process, these thin panels offer supreme flexibility and are more lightweight than their crystalline counterparts. They are also pretty durable. Some thin film solar cells have also been found to outperform their crystalline cousins in low light conditions, making it better for regions with cloudier days.

    Thin film solar cells and solar panels do have a few drawbacks though. For starters, they do not offer the same efficiency. To accommodate your electrical power needs, this may mean that you will need to install more panels than you would if you were installing a crystalline solar cell panel.

    Thin film solar cells and solar panels are also not as durable. As just a microscopic layer of silicon, it can actually break down and degrade over the course of its life. However, thin film silicone tech is advancing each year, so take these words with a grain of salt as they could become as strong as crystalline silicon. Could they become stronger? We’ll have to wait and see. For now, crystalline silicon is the silicon of choice for photovoltaics.

    Solar Energy Is Important, Now than Ever

    Solar cells and solar panels bring enormous energy through the power of the sun. Shining down on our planet is roughly 173,000 terawatts of solar energy, which for the record, is 10,000 times what we could ever really need. And as far as we know, the sun is here to stay, unlike nonrenewable resources like fossil fuels.

    Capturing the sun’s renewable energy and transforming it into electricity to power our homes and businesses can be a huge step in reducing our carbon footprint and combating climate change as a whole. We have the potential, so what’s stopping us?

    Choose Renewable Energy With Solar Panels by Unbound Solar

    The International Energy Agency has declared solar energy the world’s fastest-growing power source. But we still have a long way to go.

    There was once a time when the biggest hesitation of choosing a renewable resource like solar was the cost. However, today, the solar energy systems and solar installation costs are in decline and are more affordable – and it’s only getting better as solar technology advances. The average homeowner or business can make back their initial investment in a matter of years. Plus, with plenty of federal solar tax incentives and state solar incentives, financial help is not hard to find.

    So if you are in the market to buy solar panels to create a greener home, reduce your electric bills or help the environment, Unbound Solar is the place to be. Explore our entire selection of solar panels, including mono PERC cells and polycrystalline solar cells, for your project today. Choose solar panels made from a number of reliable, trustworthy brands, such as Astronergy, Heliene and Solaria, that are built durable and offer panel designs that integrate onto rooftops seamlessly and effortlessly.

    Whether you live in cloudier regions of the country like New York or the Pacific Northwest or have sunshine all year round, Unbound Solar has a suitable solar energy system that will capture all your energy needs so that you can live off the grid or simply cut back on energy costs for your home or business.

    But most of all – Unbound Solar solar panels put renewable energy in your own hands, so that you can combat climate change to help the earth. Shop Unbound Solar for all your solar power needs, from solar panels to grid ties to energy storage solutions like generators and solar battery banks.

    Hyundai Solar: The Complete Review

    Hyundai Solar began in 2005 by Hyundai Heavy Industries (HHI), a popular player in the heavy industries sector, with production centers in Eumseong, Korea.

    As the world’s leading shipbuilding corporation, Hyundai is also the largest solar cell and panel manufacturer in South Korea and has a solar cell production capacity of 600MW per year.

    Hyundai is considered as an economical option to homeowners looking for a low-cost solar installation. They provide high-quality PV products to more than 3,000 customers worldwide.

    Hyundai Solar Panels Applications

    Hyundai’s solar modules/panels can be used in all kinds of solar projects like

    Hyundai’s Solar Panel Features

    • Anti-LID / PID:
    • Light-Induced Degradation (LID) is a loss in cell efficiency arising in the very first hours of exposition to the sun, with Crystalline modules.
    • Potential Induced Degradation (PID) occurs over a certain period after the installation as the modules are in strings operating at high voltages, combined with very warm and humid weather. Dust and glass degradation (releasing Sodium ions) may catalyze the PID phenomenon.
    • Both LID and PID are strictly eliminated in Hyundai cells to ensure higher yield throughout its lifetime.
    • Mechanical Strength: Hyundai’s tempered glass and reinforced frame design can withstand rigorous weather conditions such as heavy snow and strong wind.
    • Reliable Warranty: As a global brand with powerful financial strength, Hyundai provides solid bankability and a good pair of warranties for its solar products.
    • 12-year product warranty on materials and workmanship.
    • In addition, Hyundai modules have a 30-year performance warranty with 97.6% in the initial year and a linear warranty after the second year (0.6% annual degradation, 80.2% is guaranteed up to 30 years).
    • Corrosion Resistant: Hyundai’s panels are tested under harsh environmental conditions such as ammonia and salt-mist and proved to highly resistant

    What Are the Different Hyundai Solar Modules?

    Currently, the following five series of Hyundai panels are available in the market:

    • RG Series
    • RG Black Series
    • RI Series
    • KI Series
    • WI AquaMax Series

    Hyundai Solar Panels Options

    Let’s look at a detailed description of these categories…


    The RG series is a 60 cell mono crystalline type solar panels that can be used for both residential and commercial applications.

    The RG series has four models – HiS-S295RG, HiS-S300RG, HiS-S305RG HiS-S310RG.

    Hyundai RG Series

    RG Series Features:

    • Depending on the models that you choose, the RG series panels deliver an output power of 295W, 300W, 305W, and 310W.
    • The advanced PERL technology makes Hyundai panels high efficient and generates more power in low light scenarios. Depending on the model you choose, the RG series panels can deliver 18.9% of efficiency.
    • As LID and PID are eliminated the Hyundai panels can give a higher yield during its lifetime.
    • These panels are highly durable as they are mechanically tough and are corrosion resistant.
    • The panels are guaranteed for quality and safety as they are manufactured in Hyundai’s RD center which is an accredited test laboratory of both UL and VDE.


    The RG Black series is a 60 cell mono crystalline type solar panels that are ideal for residential applications. The all black module with sleek design gives a better appearance.

    The RG Black series has four models – HiS-S290RG(BK), HiS-S295RG(BK), HiS-S300RG(BK) HiS-S305RG(BK).

    Hyundai RG Black Series

    RG Black Series Features:

    • Depending on the models that you choose, the RG Black series panels deliver an output power of 290W, 295W, 300W, and 305W.
    • The advanced PERL technology makes Hyundai panels high efficient and generates more power in low light scenarios. Depending on the model you choose, the RG black series panels can deliver efficiency 17.7%
    • As LID and PID are eliminated the Hyundai panels can give a higher yield during its lifetime.
    • These panels are highly durable as they are mechanically tough and are corrosion resistant.
    • The panels are guaranteed for quality and safety as they are manufactured in Hyundai’s RD center which is an accredited test laboratory of both UL and VDE.


    The RI series is a 72 cell mono crystalline type solar panels that is ideal for commercial and utility applications.

    The RI series has six models – HiS-S345RI, HiS-S350RI, HiS-S355RI, HiS-S360RI, HiS-S365RI HiS-S370RI.

    RI Series Features:

    • Depending on the models that you choose, the RI series panels deliver a superior 370W output power
    • The advanced PERL technology makes Hyundai panels high efficient and generates more power in low light scenarios. Depending on the model you choose, the RI series panels can deliver 18.9% efficiency.
    • As LID and PID are eliminated the Hyundai panels can give a higher yield during its lifetime.
    • These panels are highly durable as they are mechanically tough and are corrosion resistant.
    • The panels are guaranteed for quality and safety as they are manufactured in Hyundai’s RD center which is an accredited test laboratory of both UL and VDE.

    Hyundai RI KI Series


    The KI series is a 72 cell mono crystalline type solar panels that are suitable for utility applications. It provides a maximum system voltage of 1,500V and reduces Balance of System (BOS) costs.

    The KI series has eight models – HiS-S345KI, HiS-S350KI, HiS-S355KI, HiS-S360KI, HiS-S365KI, HiS-S370KI, HiS-S375KI, HiS-S380KI.

    KI Series Features:

    • Depending on the models that you choose, the KI series panels delivers class leading and superior 380W output power
    • The advanced PERL technology makes Hyundai panels high efficient and generates more power in low light scenarios. Depending on the model you choose, the KI series panels can deliver 19.4% efficiency.
    • As LID and PID are eliminated the Hyundai panels can give a higher yield during its lifetime.
    • These panels are highly durable as they are mechanically tough and are corrosion resistant.
    • The panels are guaranteed for quality and safety as they are manufactured in Hyundai’s RD center which is an accredited test laboratory of both UL and VDE.


    The WI series panels are suitable for floating solar plants. It provides a maximum system voltage of 1,000V and has a strong resistance to moisture.

    high-efficiency, silicon, inverted, pyramid-based, passivated

    WI Series Features:

    • The WI series panels deliver an output power of 355W – 370W
    • The advanced PERL technology makes Hyundai panels high efficient and generates more power in low light scenarios. The WI series can deliver efficiency of up to 18.9%.
    • As LID and PID are eliminated the Hyundai panels can give a higher yield during its lifetime.
    • These panels are highly durable as they are mechanically tough and are corrosion resistant.
    • The panels are guaranteed for quality and safety as they are manufactured in Hyundai’s RD center which is an accredited test laboratory of both UL and VDE.

    H ow Hyundai Solar Compares to Other Solar Makers

    The key metrics that you should review while evaluating solar panel quality are Efficiency, Power Rating, Warranty, Temperature Coefficient (Performance), and Price.


    Panel efficiency refers to the amount of sunlight that reaches a solar cell that is actually converted into electricity. For conventional silicon-based panels, this is between 14-22%. The efficiency of Hyundai panels depends on the specific model that you choose for your system. Generally, these panels have an efficiency rating of 17.2% to 19.4%.

    If you’re looking for panels suitable for residential purposes, HiS-S310RG offers a higher efficiency of 18.9%. For utility purposes, KI 380 offers a class-leading 19.4% efficiency.

    Module Series Product Number / Power Efficiency
    RG 295 18%
    300 18.3%
    305 18.6%
    310 18.9%
    RG Black 290 17.7%
    295 18%
    300 18.3%
    305 18.6%
    RI 345 17.6%
    350 17.9%
    355 18.1%
    360 18.4%
    365 18.7%
    370 18.9%
    KI 345 17.6%
    350 17.9%
    355 18.1%
    360 18.4%
    365 18.7%
    370 18.9%
    375 19.2%
    380 19.4%
    WI Aquamax 355 – 370 18.9%

    Power Rating

    All solar panels receive a nameplate power rating that indicates the amount of power they produce under industry-standard test conditions. Generally, most solar panels on the market have power ratings in the range of 200 to 350 watts. A higher power rating means that the panels are more effective at producing power. Hyundai panels offers have power ratings in the range of 295-380, making them suitable for all residential, commercial and utility applications.


    While considering a solar panel brand, make sure that the company you chose to provide a reliable warranty. Hyundai provides a 12-Year product warranty and a linear 30-Year performance warranty.

    Temperature Coefficient

    Each solar cell technology comes with unique temperature coefficients and has a direct influence on the power output of the PV modules. An increase in the temperature of a solar panel decreases its power output. A temperature coefficient of.0.5%/deg C indicates that for a one-degree rise in the temperature, the power output from the PV decreases by half of 1%. Hyundai panels have a temperature coefficient of.0.34%/°C under standard test conditions.


    The price per watt for Hyundai solar modules range from 2.83 – 3.10.

    high-efficiency, silicon, inverted, pyramid-based, passivated

    If you are looking for even more ways to lower the cost, try out our competitive bidding platform to help drive the price down.

    A 5 KW system with Hyundai panels would cost anywhere from 9,905 to 10,850 with the 30 percent federal tax credit for solar.

    Hyundai panels are considered an economical option with a solid performance and efficiency. You can think of them on the same level as their car-making business!

    Is Hyundai Solar Right for You?

    Hyundai has a wide range of good quality solar panels. But the best way to decide is to review multiple quotes with different solar equipment options.

    • You can compare all of your options on’s Marketplace, you’ll find the right combination of price and quality that meets your needs.
    • Be sure to review our guide on the best solar panels to understand the key metrics you should use to compare solar modules against one another.

    G et in touch with one of our experienced Energy Advisers to see if Hyundai is right for your home!

    PERC solar cell technology: why will it dominate in the near future?

    In recent years, PERC solar cell technology (from the English. Passivated Emitter Rear Cell) has become one of the favorites of research and development in the photovoltaic industry. Today it is considered one of the top advanced technologies in the production of high-performance solar panels.

    What is PERC

    The production of photovoltaic cells has been dominated for many years by one Al-BSF modular technology with an aluminum backing However, it is close to its practical limit, and further improvement in efficiency is unlikely. This is because for many years, manufacturers have focused on developing innovations for the front side of the solar cell, not paying due attention to its reverse side. The search for solutions to improve efficiency has prompted the solar industry to use passive emitter rear contact (PERC) solar cells. In fact, PERC technology has become a procedure for improving standard Al-BSF photovoltaic cells. The PERC photocells provided access to the module with a higher power rating, for example up to 370W for a 72 cell module.

    The abbreviation PERC stands for emitter back contact passivation (literally, passivated emitter and rear cell/module). The main feature of solar panels with PERC technology is that a dielectric layer is located on the reverse side of the module. It reflects the light rays that have passed through the photocell and redirects them back inside the silicon layers. This generates more electricity. This process is otherwise known as backside passivation. PERC technology helps to increase the spectral sensitivity of photovoltaic cells, which is achieved due to the ability to absorb a larger amount of sunlight.

    PERC technology was developed in 1980 in Australia by a group of scientists led by the director of the Australian Center for Advanced Photovoltaics at UNSW (University of New South Wales), Professor Martin Green, but it began to be actively used only 5–6 years ago.

    Due to its merits, in the last two or three years, PERC technology has become a priority for manufacturers of both poly- and monocrystalline panels.

    How PERC technology works

    Compared to traditional panels, modules with PERC technology have higher performance. Using this innovation is a good way to increase the reflectivity of the back surface of a solar cell by increasing the number of photons that can be absorbed and converted into more electricity produced.

    Photoelectronic emission is a rather complicated process. The power generator in photomodules consists of two parts: a base and an emitter with a pn contact zone – the boundary between them. It is here, at the boundary section of the transition, that an electric current is generated, the electrons rush to the emitter. A similar scheme for the production of electrical energy is used in PERC modules.

    The task of solar panels is to produce electric current, and the principle of its production is as follows. Photons (particles of light) seem to “knock out” electrons (negative particles) from the silicon layer. Both those and other particles have the property of “wandering”. In order for an electric current to be generated, an electron “knocked out” of silicon must reach the contact boundary. But, as a rule, most of the negative particles (electrons) simply settle in the lower layer of the base. That is why the efficiency of modern solar panels does not exceed 20%.

    If we compare a traditional solar cell and a panel with PERC technology, then in the first case, the rear contactor is a thin layer of aluminum that acts as a continuous current collector, and in the second case, PERC photocells use a layer of aluminum with sputtering and laser perforation. Thus, in the additional layer there are numerous microholes through which electrons escape. Due to the dielectric properties of the back layer in PERC photovoltaic cells, the electrons that settle at the bottom are again redirected until they find a hole in the perforation in order to go to the emitter.

    In fact, an additional dielectric passivating layer reduces the recombination of electrons (the process of the disappearance of a pair of particles – free carriers of the opposite charge to any medium with the release of energy). In other words, this means the tendency for electrons to recombine and basically block electrons from wandering freely through the solar cell, causing it to fail to reach its potential efficiency. In the case of using an additional dielectric layer, the electrons generated near the back of the PV module can freely move up to the emitter and contribute to the increase in electric current generation, which means that the efficiency of the solar panel with PERC technology is increased.

    The additional dielectric passivation layer can reflect wavelengths above 1180 nanometers outside of the photocell, which normally generates heat. In standard photomodules, such wavelengths are easily absorbed by the back of the metallized side of the photocell and transformed into heat, which reduces the efficiency of solar panels. By reflecting wavelengths above 1180 nanometers, the dielectric passivation layer in PERC modules helps the PV cell operate more efficiently without overheating.

    Several other types of PERC photovoltaic cells have also been developed, such as PERL (passivated rear emitter, locally scattered) and PERT (passivated rear emitter, fully diffused). However, they are not yet widely used.

    Benefits of PERC Technology

    When it comes to research and development in the solar energy industry, there are two main goals that manufacturers and consumers strive to achieve: cost reduction and efficiency improvement Solar cells with PERC technology have an efficiency of over 20-22%, while standard solar cells average around 18-19%. For example, improving the efficiency of photovoltaic cells due to PERC technology leads to an increase in power by 3-5 W for a single crystal module. with 60 elements.

    Among the main advantages of PERC modules are the following.

    • PERC technology can be used in both mono- and polycrystalline panels.
    • The use of PERC technology increases the efficiency of solar modules by up to 25% due to an increase in the absorbing capacity of the photocell, reducing unwanted overheating in it, reflecting already generated electrons into the pn junction zone, which is recognized as one of the highest values in the industry.
    • The production of photovoltaic modules using PERC technology is very different from the production of conventional photovoltaic cells, since only the back surface is modified by simply adding a dielectric layer and using lasers for holes (perforations). Thus, the installation of some special complex equipment is not required, it is enough to modernize existing production lines. That is, solar panels with PERC technology have a higher power output with minimal investment and few risks.
    • When operating PV cells with PERC technology, short circuit currents increase, resulting in an increase in current strength, which simultaneously increases the voltage and, as a result, the output power of the solar panel.
    • The reflectivity of panels with PERC technology increases to 90-95% compared to 65% for panels of typical configurations.
    • PERC elements perform well in high temperature or low light environments.
    • Due to more attractive temperature coefficients, solar panels with PERC technology are the best solution for use in hot climates, helping to reduce heat loss. As a result, end users get maximum efficiency from their solar systems throughout the year.
    • Installing solar panels with PERC technology is more cost effective than traditional solar panels. The innovation itself affects the cost of the finished solar plant insignificantly, but at the same time significantly increases its efficiency. In addition, to produce the same amount of electricity as a standard solar panel, PERC technology typically requires fewer photovoltaic cells.

    Why is PERC technology chosen by solar cell and panel manufacturers?

    The investment to switch to a PERC production line requires minimal modifications to existing cell production lines. Manufacturers can easily transition to producing a quality and efficient product without making large capital investments to completely replace existing equipment. There is a boom in the world market in the direction of increasing the capacity for the production of modules with PERC technology. Experts predict that this process will develop rapidly over the next few years. In addition, panel manufacturers can now produce a more energy-intensive module without significantly increasing assembly costs.

    Why is PERC preferred by panel engineers and installers?

    Panels with PERC technology give more freedom to panel installers, especially when it comes to spaces or places that were previously considered insufficient for solar installations. PERC panels have a higher energy density per square meter. m and work well in low light and high temperatures. Clearly, when generating power, PERC panels are superior to standard counterparts. Solar designers can use fewer panels to achieve overall “output” energy goals when their footprint is limited. Also, panels with PERC technology without loss of efficiency can be installed in places and spaces that were previously considered unsuitable for solar energy facilities. This allows engineers and installers to be more flexible and better able to adapt to project goals.

    Why is PERC technology cost effective?

    Since the production of panels with PERC technology is not radically different from the production of standard panels, the risk of investment, which is often associated with any know-how, is reduced. Using proven technology and modifying standard panels, there is virtually no risk that the introduction of PERC technology will drastically change the structure and interior of the photocell. That is, the funds will not be “thrown to the wind.”

    The ultimate goal of PERC panel manufacturing is to provide a reliable and cost-effective way to generate energy for residential, commercial and utility projects. When using solar panels with PERC technology, the total electricity generation over the lifetime of the entire solar plant is increased without a significant increase in cost per watt.

    Why will PERC be the dominant solar cell technology?

    The prospects for PERC modules seem promising, and the current level of scientific and technological progress makes it possible to put the production of such solar panels on the conveyor. Today, many recognized brands of solar panels have already introduced PERC technology into production. Among them are Canadian Solar, LG, REC Solar, Winaico, Trina Solar, Jinko Solar, Solar World, etc.

    PERC technology will dominate in the coming years, not only due to its advantages, but mainly because it does not require a complete retooling of production. For example, manufacturers can easily upgrade existing production lines because PERC is compatible with existing screen printing equipment. And there are many such engineering solutions.

    According to experts, in the coming years, solar panels with PERC technology will be much more attractive in price for the mass consumer than traditional solar panels. But so far, such photomodules (PERC) are an order of magnitude more expensive than standard counterparts. A significant price reduction can be seen only against the backdrop of mass production and the increasing popularization of PERC technology. Therefore, already now, understanding the prospects and advantages of such solar panels, an increasing number of solar panel manufacturers are rebuilding their production facilities to introduce PERC technology.

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