Amorphous Silicon Solar Cells Research Articles

Analytical energy-barrier-dependent Voc model for amorphous silicon solar cells

We show that the open circuit voltage (Voc) in hydrogenated amorphous silicon (a-Si:H) solar cells can be described by an analytical energy-barrier-dependent equation, considering thermionic emission as the physical mechanism determining the recombination current. For this purpose, the current-voltage characteristics of two device structures, i.e., a-Si:H(n)/a-Si:H(i)/a-Si:H(p)/AZO p-i-n solar cells with different p-doping concentrations and a-Si:H(n)/a-Si:H(i)/AZO Schottky structures with different intrinsic layer thicknesses, were analyzed in dark and under illumination, respectively. The calculated barrier in the p-i-n devices is consistent with the difference between the work function of the p-layer and the conduction band edge of the i-layer at the interface in thermal equilibrium.

Light Entrapping, Modeling & Effect of Passivation on Amorphous Silicon Based PV Cell

This research paper present efforts to enhance the performance of amorphous silicon p-i-n type solar cell using sidewall passivation. For sidewall passivation, MEMS insulation material Al2O3 was used. The main objective of this paper is to observe the effect of sidewall passivation in amorphous silicon solar cell and increase the conversion efficiency of the solar cell. Passivation of Al2O3 is found effective to subdue reverse leakage. It increases the electric potential generated in the designed solar cell. It also increases the current density generated in the solar cell by suppressing the leakage. Enhancement in J-V curve was observed after adding sidewall passivation. The short circuit current density (Jsc) increased from 14.7 mA/cm2 to 18.5 mA/cm2, open circuit voltage (Voc) improved from 0.87 V to 0.89 V, and the fill factor also slightly increased. Due to the sidewall of passivation of Al2O3, conversion efficiency of amorphous silicon solar cell increased by 29.07%. At the end, this research was a success to improve the efficiency of the amorphous silicon solar cell by adding sidewall passivation.

Development of wide band gap p-a-SiOxCy:H using additional trimethylboron as carbon source gas

We report p-type a-SiOxCy:H thin films which were fabricated by introducing additional Trimethylboron (TMB, B(CH3)3) doping gas into conventional standard p-type a-SiOx:H films. The TMB addition into the condition of p-a-SiOx:H improved optical bandgap from 2.14 to 2.20 eV without deterioration of electrical conductivity, which is promising for p-type window layer of thin film solar cells. The suggested p-a-SiOxCy:H films were applied in amorphous silicon solar cells and we found an increase of quantum efficiency at short wavelength regions due to wide bandgap of the new p-layer, and thus efficiency improvement from 10.4 to 10.7% was demonstrated in a-Si:H solar cell by employing the p-a-SiOxCy:H film. In case of a-SiOx:H cell, high open circuit voltage of 1.01 V was confirmed by using the suggested the p-a-SiOxCy:H film as a window layer. This new p-layer can be highly promising as a wide bandgap window layer to improve the performance of thin film silicon solar cells.

Flexible Electronics: High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells (Adv. Mater. 28/2016).

On page 5939, J. V. Badding and co-workers describe the unrolling of a flexible hydrogenated amorphous silicon solar cell, deposited by high-pressure chemical vapor deposition. The high-pressure deposition process is represented by the molecules of silane infiltrating the small voids between the rolled up substrate, facilitating plasma-free deposition over a very large area. The high-pressure approach is expected to also find application for 3D nanoarchitectures.

Low Reverse Saturation Current Density of Amorphous Silicon Solar Cell Due to Reduced Thickness of Active Layer

One of the most important characteristic curves of a solar cell is its current density-voltage (J-V) curve under AM1.5G insolation. Solar cell can be considered as a semiconductor diode, so a diode equivalent model was used to estimate its parameters from the J-V curve by numerical simulation. Active layer plays an important role in operation of a solar cell. We investigated the effect thicknesses and defect densities (N_d) of the active layer on the J-V curve. When the active layer thickness was varied (for N_d = 8×10¹⁷ cm^-3) from 800 nm to 100 nm, the reverse saturation current density (J_o) changed from 3.56×10^-5 A/cm² to 9.62×10^-11 A/cm² and its ideality factor (n) changed from 5.28 to 2.02. For a reduced defect density (N_d = 4×10¹⁵ cm^-3), the n remained within 1.45≤n≤1.92 for the same thickness range. A small increase in shunt resistance and almost no change in series resistance were observed in these cells. The low reverse saturation current density (J_o = 9.62×10^-11 A/cm²) and diode ideality factor (n = 2.02 or 1.45) were observed for amorphous silicon based solar cell with 100 nm thick active layer.

Correlation between SiH2/SiH and light-induced degradation of p–i–n hydrogenated amorphous silicon solar cells

We have measured the hydrogen content ratio ISiH2/ISiH associated with Si–H2 and Si–H bonds in p–i–n (PIN) a-Si:H solar cells by Raman spectroscopy. With decreasing ISiH2/ISiH, the efficiency, short-circuit current density, open-circuit voltage, and fill factor of PIN a-Si:H solar cells after light soaking tend to increase. Namely, ISiH2/ISiH correlates well with light-induced degradation of the cells. While a single I-layer has a low ISiH2/ISiH of 0.03–0.09, a PIN cell has ISiH2/ISiH = 0.18 because many Si–H2 bonds exist in the P-layer and at the P/I interface of the PIN solar cells. To realize PIN solar cells with higher stability, we must suppress Si–H2 bond formation in the P-layer and at the P/I interface.

Thermal residual stresses in silicon thin film solar cells under operational cyclic thermal loading: A finite element analysis

In manufacturing amorphous silicon solar cells, thin films are deposited at high temperatures (200–400°C) on a thick substrate using sputtering and plasma enhanced chemical vapor deposition (PECVD) methods. Since the thin films and substrate have different thermal expansion coefficients, cooling the system from deposition temperature to room temperature induces thermal residual stresses in both the films and substrate. In addition, these stresses, especially those having been induced in the amorphous silicon layer can change the carrier mobility and band gap energy of the silicon and consequently affect the solar cell efficiency. In this paper, a 2D finite element model is proposed to calculate these thermal residual stresses. The model is verified by the available analytical results in the literature. Then using the model, the thermal residual stresses are studied in a commercial amorphous silicon thin film solar cell for different deposition temperatures, and subsequently, the simulation results are validated with experimental results. It is shown that for the deposition temperatures of 200 and 300°C, the biaxial thermal stress reaches the values of −367 and −578MPa, respectively, in the amorphous silicon layer. Finally, the model is utilized to study the cyclic thermal stresses arising in the solar cell installed in Tehran as a sample city during its operational time due to the ambient temperature changes and photovoltaic process. The results are reported for different months based on the minimum and maximum temperatures published during a year. It is demonstrated that the temperature changes can induce mean stress with stress amplitude of −526 and 60MPa, respectively, in the amorphous silicon layer during June, for example. The calculated loading history can be used by the manufactures in thermal fatigue life assessment of the solar cell.

Efficiency enhancement via metal-coated porous amorphous silicon back reflectors incorporated in amorphous silicon solar cells

Abstract

Modify the Schottky contact between fluorine-doped tin oxide front electrode and p-a-SiC:H by carbon dioxide plasma treatment

Carbon dioxide plasma (COP) treatment of a fluorine-doped tin oxide (SnO2:F, FTO) front electrode was used for the fabrication of p–i–n hydrogenated amorphous silicon (a-Si:H) solar cells. The oxygen and carbon monoxide radicals in COP play important roles of de-doping and doping effects on the surface of FTO, respectively. Through changing the COP treatment time, the de-doping and doping effects could alter the number of oxygen vacancies for both the bulk and the surface of FTO, resulting in an increase in the work function (WF) and a decrease in the Schottky barrier at the p-a-SiC:H/FTO interface. Due to an increase in the WF from 4.16eV to 4.34eV after 95s treatment, the open circuit voltage (Voc) of the a-Si:H solar cells increased from 915mV to 965mV and the fill factor (FF) increased from 67.7% to 74.4%. Although the short-circuit current density (Jsc) decreased from 11.76mA/cm2 to 10.36mA/cm2 after 95s COP treatment due to the weakness of Burstein–Moss (BM) shift and the recombination at FTO surface, the conversion efficiency of the a-Si:H solar cell was enhanced by 12.24% after 45s COP treatment, accompanied by improving the Voc and FF with almost constant Jsc.

High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells.

Thin films of hydrogenated amorphous silicon can be produced at MPa pressures from silane without the use of plasma at temperatures as low as 345 °C. High pressure chemical vapor deposition may open a new way to low cost deposition of amorphous silicon solar cells and other thin film structures over very large areas in very compact, simple reactors.

Efficiently-cooled plasmonic amorphous silicon solar cells integrated with a nano-coated heat-pipe plate.

Solar photovoltaics (PV) are emerging as a major alternative energy source. The cost of PV electricity depends on the efficiency of conversion of light to electricity. Despite of steady growth in the efficiency for several decades, little has been achieved to reduce the impact of real-world operating temperatures on this efficiency. Here we demonstrate a highly efficient cooling solution to the recently emerging high performance plasmonic solar cell technology by integrating an advanced nano-coated heat-pipe plate. This thermal cooling technology, efficient for both summer and winter time, demonstrates the heat transportation capability up to ten times higher than those of the metal plate and the conventional wickless heat-pipe plates. The reduction in temperature rise of the plasmonic solar cells operating under one sun condition can be as high as 46%, leading to an approximate 56% recovery in efficiency, which dramatically increases the energy yield of the plasmonic solar cells. This newly-developed, thermally-managed plasmonic solar cell device significantly extends the application scope of PV for highly efficient solar energy conversion.

Dual-Layer Nanostructured Flexible Thin-Film Amorphous Silicon Solar Cells with Enhanced Light Harvesting and Photoelectric Conversion Efficiency.

Three-dimensional (3-D) structures have triggered tremendous interest for thin-film solar cells since they can dramatically reduce the material usage and incident light reflection. However, the high aspect ratio feature of some 3-D structures leads to deterioration of internal electric field and carrier collection capability, which reduces device power conversion efficiency (PCE). Here, we report high performance flexible thin-film amorphous silicon solar cells with a unique and effective light trapping scheme. In this device structure, a polymer nanopillar membrane is attached on top of a device, which benefits broadband and omnidirectional performances, and a 3-D nanostructure with shallow dent arrays underneath serves as a back reflector on flexible titanium (Ti) foil resulting in an increased optical path length by exciting hybrid optical modes. The efficient light management results in 42.7% and 41.7% remarkable improvements of short-circuit current density and overall efficiency, respectively. Meanwhile, an excellent flexibility has been achieved as PCE remains 97.6% of the initial efficiency even after 10 000 bending cycles. This unique device structure can also be duplicated for other flexible photovoltaic devices based on different active materials such as CdTe, Cu(In,Ga)Se2 (CIGS), organohalide lead perovskites, and so forth.

Solar‐to‐Hydrogen Efficiency of 9.5 % by using a Thin‐Layer Platinum Catalyst and Commercial Amorphous Silicon Solar Cells

AbstractA photoelectrochemical system was set up with commercial triple‐junction solar cells to split water into hydrogen. To minimize the Pt loading and material cost and to maintain a high catalytic activity, a thin Pt layer on a high‐surface‐area Ni foam was used to catalyze the hydrogen evolution reaction. The solar‐to‐hydrogen efficiency measured from the hydrogen gas evolved is as high as 9.5 %.

The analysis of the efficiency of solar cells

Under the circumstances of the increasing depletion of fossil fuels, renewable energy, especially solar energy, is becoming more and more important. Thus, the methods of exploring solar energy are diverse and the energy conversion efficiency keeps rising while the cost keeps decreasing. Among all the methods, using solar cell is the main way to explore solar energy. Currently, solar cells can be divided into three main categories, crystalline silicon solar cells, thin film solar cells and novel solar cells. Crystalline silicon solar cells can also be divided into monocrystalline silicon solar cell and polycrystalline silicon solar cell. These two kinds of solar cells are the most common solar cells in our daily life. The efficiency of monocrystalline silicon solar cell is already pretty high reaching 25% while polycrystalline silicon solar cell reaches 21.3%. The stability of monocrystalline silicon solar is also better than that of polycrystalline silicon solar cell. The only fly in the ointment is that the cost of monocrystalline silicon solar is a little bit higher than polycrystalline silicon solar cell which makes monocrystalline silicon solar not optimal enough. Thin film solar cell includes amorphous silicon solar cells and multi-compounds solar cells. The transformation of solar cells from solid panel to thin film is one of the most significant breakthroughs of the second generation solar cell. The amorphous silicon solar cell becomes much cheaper than both monocrystalline silicon and polycrystalline silicon solar cells. But its drawback is obvious, its efficiency only reaches 13.6% which certainly needs to be improved. As for semiconductor compounds solar cells, there are made by various semiconductor materials. Major semiconductor compound solar cells contain chemical materials such as CdTe, CuInSe2(CIS), CuInSe2 doped Ga(CIGS), GaAs, InP, and multi-junction solar cell, etc. Materials like CdTe and CIGS can surely lower the cost of solar cells and their efficiencies are pretty high reaching 21.5% and 22.3%, respectively. But Cd is a toxic element while In and Se are rare elements, their reserves are limited. Materials like GaAs and InP are much more expensive comparing to others, but their efficiencies are pretty satisfying reaching 28.8% and 22.6%, respectively. More importantly, they have rather high radiation tolerance, especially InP solar cell has the best radiation tolerance among all kinds of solar cells. Thus, despite their high costs, they can still be used in many situations such as space station. As for multi-junction solar cell, the most prominent feature of it is the high efficiency. Solar cells with two junctions, three junctions and four junctions have reached the efficiencies of 31.6%, 37.9% and 38.8%. Obviously, multi-junction solar cells are the best choice to improve energy conversion efficiency. The novel solar cell consists of organic solar cells, dye-sensitized solar cells, quantum dot solar cells and hybrid perovskite solar cells. Among all these third generation solar cells, perovskite solar cell is the most promising one due to its superior properties and rapid improvement. Its efficiency has already reached 21% in only a few years. But more work needs to be done to improve its properties such as its stability and currently perovskite solar cell still contains lead which is toxic and may need to be replaced. This paper starts from analyzing the theoretical efficiency of solar cells, then compares those theoretical efficiencies with experimental efficiencies to present the expectation of different kinds of solar cells.

Window p-layer in amorphous pin solar cells using ZnO as Transparent Conductive Oxide

The main steps of p-layer development in pin thin film amorphous silicon solar cell at TEL Solar are presented. First, the implementation of a new PECVD reactor is shown to contribute to an improvement in amorphous silicon carbide (a-SiC) p-layer quality probably by reducing the porosity and leading to an increased open circuit voltage after the solar cell is subjected to light soaking. Second, an alternative high flow deposition regime for the p-doped a-SiC layer was successfully developed improving the layer purity and electrical conductivity. And third, a softer deposition regime for the very first part of the p-layer, the contact layer, which plays a crucial role in the release of Zn from the TCO, contributes to a decreased overall Zn contamination.

Light management in flexible thin‐film solar cells on transparent plastic substrates

Maintaining efficient light management is an essential part for obtaining high efficiency flexible thin‐film solar cells. Transparent plastic films like polyethylene terephthalate (PET) are a cost efficient substrate alternative but also impose additional constraints on the light management approaches available. In this study, we investigate and compare two approaches to prepare substrates with light scattering characteristics. We have developed low temperature ZnO:Al layers, which are fully compatible with PET substrates, and are textured by wet‐chemical methods. These low temperature textured ZnO:Al layers implemented in amorphous silicon solar cells on glass substrates result in similar efficiencies as highly optimized high temperature‐etched ZnO:Al layers. Nanoimprint lithography was used as an alternative light management approach and we show that an improved solar cell performance can be achieved on flexible PET substrates with both methods. Besides the effect on solar cell performance, pros and cons of both approaches with respect to flexibility in choice of materials and textures, fabrication process, stress evolution, and reproducibility are discussed.

Effect of Sputtered Zinc Oxide as Anti- Reflection Coating in Amorphous Silicon Solar Cell

Effect of Sputtered Zinc Oxide as Anti- Reflection Coating in Amorphous Silicon Solar Cell

Temperature dependence of hydrogenated amorphous silicon solar cell performances

Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the a-Si:H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the Voc generally varies linearly with the Voc value. The Jsc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the Pmpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the Pmpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy yield. However, for a different climate or cell configuration, this may not be true.

Enhanced performance of thin-film amorphous silicon solar cells with a top film of 2.85 nm silicon nanoparticles

The performance of thin-film amorphous silicon-based n+-i-p+ solar cells in the presence of an exterior top thin film of mono-dispersed ultra-small 2.85nm diameter silicon nanoparticles has been examined. The silicon nanoparticles have a 530–700nm red luminescence band with a band peak at 628nm. Reflectance and the external/internal quantum efficiency (EQE/IQE) of the devices were measured over the range of 300–800nm. With the Si NPs there is a reduction in reflectivity, which improves the coupling of light to the solar cell. The enhancement in IQE is found to be over the spectral slice 360–610nm lying between the confinement and the direct band gaps. An enhancement in the IQE in the range of 390–530nm with a maximum of 31% at 445nm and a smaller one in the range of 530–610nm with a maximum of 11% at 590nm was observed. The increase in the spectral response corresponds to 11.42% increase in short circuit current in agreement with our J–V measurements. The IQE enhancement is explained in terms of two competing channels: excitonic radiative recombination down-conversion in the range 530–610nm and charge separation and collection in the range 360–530nm.

Measurement and Calculation of Luminous Characteristics of Photovoltaic Glazing Samples

Photovoltaic glazing is a relatively novel type of glazing material, suitable for application in nearly-zero energy buildings. As a special type of building integrated photovoltaic (BIPV), it generates energy from solar radiation and ensures the performance characteristics of building envelope. This paper presents a combined approach of evaluation of luminous characteristics of glazing based on photopic and circadian action spectra. Measurements were performed on 6 photovoltaic glazing samples with amorphous silicon solar cells. The samples differ in type of spacing and rear glazing colour. The results have shown that PV glazing with coloured glazing should be used with caution, especially in rooms with high daylighting requirements. Obtained results can be used during designing process to evaluate impact of PV glazing on visual comfort.