CuInSe2 cells and modules

Recent CuInSe₂ photovoltaic technology advances are discussed. 14.1% active area efficient test cells and the fabrication of monolithic integrated modules with power outputs of 112 W/m² on 940 cm² and 91.4 W/m² on 3900 cm² have been achieved. Packaged modules are stable outdoors. Studies indicate a recombination controlled junction mechanism and imply a wide CIS compositional range over which high-efficiency junctions are possible. Processing improvements already demonstrated on test cells and 940 cm² modules will yield 52-W, 3900-cm² CIS modules     

Computer simulation and modeling of graded bandgap CuInSe2/CdS based solar cells

This paper proposes the graded bandgap absorber material, Cu_1-xAg_xIn_1-y-zGa_yAl_z Se/sub 2(1-u$/ -/sub w/)S_2uTe_2w (CIS*) multinary system, to improve the low open-circuit voltage (V_OC) seen in CuInSe₂/CdS solar cells, without sacrificing the short-circuit current density (J_sc). It also proposes a p-i-n model for the CuInSe₂/CdS solar cell, where the intrinsic region is the graded bandgap CIS*. Reflecting surfaces are provided at the p-i and n-i interfaces to trap the light in the narrow intrinsic region for maximum generation of electron and hole pairs (EHP's). This optical confinement results in a 25-40% increase in the number of photons absorbed. An extensive numerical simulator was developed, which provides a 1-D self-consistent solution for Poisson's equation and the two continuity equations for electrons and holes. This simulator was used to generate J-V curves to delineate the effect of different grading profiles on cell performance. The effects of a uniform bandgap, normal grading, reverse grading, and a low bandgap notch have been considered. Having established the inherent advantages to these grading profiles an optimal doubly graded structure is proposed with grading between 1.5 eV and 1.3 eV regions which has V_OC=0.86 V, η=17.9%, FF=0.79 and J_sc=26.3 mA/cm² compared to 0.84 V, 14.9%, 0.76, and 23.3 mA/cm², respectively, for the highest efficiency 1.4-eV uniform bandgap cell. Replacing the thick CdS(2.42 ev) layer assumed in our simulations with a wide gap semiconductor such as ZnO(3.35 ev) increases all current densities by about 5 mA/cm², and increases the optimal calculated efficiency from 17.9% to roughly 21% for a doubly graded structure with a thickness of 1 μm and bandgaps ranging from 1.3 eV to 1.5 eV     

High-efficiency GaAs/Ge monolithic tandem solar cells

Tandem cells of GaAs grown by metalorganic chemical vapor deposition (MOCVD) on thin Ge to address both higher efficiency and reduced weight are discussed. GaAs/Ge monolithic tandem cells of 4-cm ² area have been produced with independently verified efficiencies up to 21.7% (AM0, one sun, 25°C, total area). Under AM1.5 global conditions, efficiencies are up to 24.3%. These are believed to be the highest one-sun efficiencies reported for GaAs/Ge cells, and the highest efficiency for a two-terminal monolithic tandem cell     

Over 35-percent efficient GaAs/GaSb tandem solar cells

The efficiency of GaAs solar cells can be substantially increased by locating an infrared-sensitive booster solar cell behind a transparent GaAs cell. Infrared-sensitive GaSb cells and visible-light-sensitive GaAS cells designed for use with concentrated sunlight are described. Prismatic cover slides are used to effectively eliminate grid shading losses for both the GaAs and the GaSb cells. With prismatic cover slides, the best component cell efficiencies add up to 38.2% under concentrated sunlight (100×AM1.5D). Two-terminal tandem cell circuit cards containing nine transparent GaAS cells and nine GaSb cells are also described. Without cell prismatic covers, circuit-level energy conversion efficiencies near 30% (AM1.5D) are demonstrated     

Electrical properties of CuInSe2 single crystals

Various bulk electrical properties and device characteristics have been measured. It has been shown that the majority carrier type is dependent on crystal stoichiometry. Mobilities of 660 cm²/V sec and 30 cm²/V sec have been measured for n-and p-type samples, respectively. Rectifying contacts and p-n junctions have been investigated by small signal analysis and the associated doping levels and equilibrium band diagrams have been determined. Photovoltage measurements on rectifying contacts have shown that the band-gap has a value of 0.95 ± 0.01eV.     

Metal-free indoline-dye-sensitized TiO2 nanotube solar cells

Titanium dioxide nanotubes were directly fabricated from commercial P25 TiO₂ via alkali hydrothermal transformation. The prepared titanate nanotubes were successfully used as an electrode material for dye-sensitized solar cells (DSCs). A metal-free organic dye (indoline dye D102) was used as a sensitizer. The used indoline dye D102 is of high purity (?98%) and high absorption coefficient (67,500 L mol⁻¹ cm⁻¹ at 501 nm). The TiO₂ pastes were prepared with PEG (Mw 20,000) and as-made TiO₂ nanotubes or P25 powders. Titania thin films were grown by screen printing method. High conversion efficiencies of light to electricity of around 9.8% and 7.6% under illumination of simulated AM1.5 sunlight (100 mW/cm²) were achieved with P25 and TiO₂ nanotube cells, respectively. The fill factor of DSCs based on TiO₂ nanotubes increased in comparison with that of DSCs based on TiO₂ nanoparticles. The electron transport and dye adsorption properties in both titanate nanotube and P25 electrodes were evaluated in terms of photovoltaic characteristics of the fabricated cells. The related mechanisms were discussed. The study provides a promising method for the development of high-efficiency and low-cost DSCs.     

大面积、高性能柔性 GaInP/GaAs/InGaAs叠层太阳电池的制备

柔性高效Ⅲ-Ⅴ族多结太阳电池正在被开发、应用于无人机、可穿戴设备和空间能源等领域.采用MOCVD技术在Ga As衬底上制备太阳电池外延层, 之后通过低温键合和外延层剥离方法将外延层转移到柔性衬底上.通过外延层剥离设备设计和大量参数优化实验, 实现了GaAs太阳电池结构从四英寸砷化镓晶圆上的有效分离, 且不产生缺陷并保持原有的性能.近期, 在50μm聚酰亚胺薄膜上制备的30 cm2大面积柔性GaInP/Ga As/InGaAs三结太阳电池实现了31. 5%的转换效率 (AM0光谱) , 其中开路电压3. 01 V, 短路电流密度16. 8 mA/cm2, 填充因子0. 845.由于采用了轻质的聚酰亚胺材料, 所得到的柔性太阳电池面密度仅为168. 5 g/m2, 比功率高达2 530 W/kg.     

CuInSe2薄膜太阳能电池非真空印刷制备技术研究

对CuInSe2(CISe)薄膜太阳能电池的吸收层进行了非真空印刷制备技术研究。使用机械化学法合成CISe前驱粉末,采用ethyl-cellulose作为分散试剂配置印刷浆,使用丝网印刷技术沉淀CISe吸收层,对沉淀的吸收层进行N2氛围的快速热退火处理,使用XRD、UV、SEM及J-V等手段对CISe吸收层进行了分析表征。结果表明:简单高效的机械化学法可获得主(112)晶向CISe前驱粉末;经丝网印刷并干燥后的CISe吸收层中含有大量有机分散剂,退火可蒸发有机分散剂并有效改善CISe结晶度,但过长的退火会增加晶体缺陷;实验制得一典型CISe薄膜太阳能电池的短路电流密度、开路电压、填充因子和转换效率分别为4.48mA/cm2、355mV、0.41和0.65%。     

Enhanced efficiency in GaInP/GaAs tandem solar cells using carbon doped GaAs in tunnel junction

Carbon doping of GaAs using CBr₄ (carbon tetrabromide) in metal-organic chemical vapor deposition (MOCVD) was investigated to obtain very high and sharp doping profiles required for tunnel junction in tandem solar cells. It was found that the hole concentration increased with decreasing growth temperature and V/III ratio. Hole doping profiles versus distance from the sample surface showed that the hole concentration near the surface was very low in comparison with that far below the surface. As a post-growth treatment, CBr₄ was supplied during the cool down process and produced almost constant hole concentration of 1 × 10²⁰ cm⁻³ regardless of the depth, when CBr₄ flow rate was 9.53 μmol/min. Based on these results, solar cells were fabricated using both carbon (C) and zinc (Zn) as a p-type dopant. It was shown that C doping exhibits higher efficiency and lower series resistance than those of Zn doping in GaInP/GaAs tandem solar cells.     

25.5% efficient Ga0.35In0.65P/Ga0.83In0.17As tandem solar cells grown on GaAs substrates

Theoretical calculations predict a higher power conversion efficiency for the combination of Ga_0.35In_0.65P and Ga_0.83In_0.17As in a tandem solar cell, compared to the more commonly used Ga_0.51In_0.49P/GaAs approach. A record conversion efficiency of 21.6% (AM1.5 g) was recently achieved for a 1.18 eV Ga_0.83In_0.17As solar cell, grown lattice-mismatched to the GaAs substrate material. This paper reports on the device characteristics of first Ga_0.35In_0.65P/Ga_0.83In_0.17As tandem solar cells based on this very promising GaInAs material. A high quantum efficiency, comparable to the lattice-matched Ga_0.51In_0.49P on GaAs approach was achieved. A power conversion efficiency of 25.5% was measured under AM1.5d spectral conditions     

Large-area, 8-cm2 GaAs solar cells fabricated from MBEmaterial

A GaAs solar cell with an area of 2 cm×4 cm fabricated from a film grown by molecular beam epitaxy (MBE) on a 5.08-cm-diameter GaAs substrate is discussed. This is the largest device ever fabricated from MBE material. The cell demonstrated an efficiency of 21.7% under one-sun AM1.5 conditions at 25°C and 18.8% under one-sun AM0 conditions at 28°C     

High-efficiency dual-junction GaInP/GaAs tandem solar cells obtained by the method of MOCVD

Monolithic dual-junction GaInP/GaAs solar cells grown by the MOCVD method were studied. The conditions of the growth of ternary Ga _x In_1?x P and Al _x In_1?x P alloys lattice-matched to GaAs are optimized. Technology for fabrication of a tunneling diode with a high peak current density of 207 A/cm² on the basis of heavily doped n ⁺⁺-GaAs:Si and p ⁺⁺-AlGaAs:C layers is developed. Cascade GaInP/GaAs solar cells obtained as a result of relevant studies featuring a good efficiency of the solar-energy conversion both for space and terrestrial applications. The maximum value of the GaInP/GaAs solar-cell efficiency was 30.03% (at AM1.5D, 40 suns).     

Perovskite/organic tandem solar cells

<正>In recent years, the power conversion efficiency (PCE) for single-junction perovskite solar cells (PSCs)[1,2]has reached25.7%, approaching the Shockley-Queisser limit (S-Q limit). Further enhancing efficiency is challenging. Tandem solar cells offer an effective way to further increase the efficiency beyond S-Q limit. Currently, perovskite/silicon tandem solar cells(TSCs)[3-5] have achieved a PCE of 31.3%[6]. However,     

AlGaAs/GaAs superlattice solar cells

A theoretical model is performed to study the viability of the AlGaAs/GaAs superlattice solar cell (SLSC). Using the Transfer Matrix Method, the conditions for resonant tunneling are established for a particular SL geometry with variably spaced quantum wells. The effective density of states and the absorption coefficient are calculated to determinate the J–V characteristic. Radiative, non‐radiative, and interface recombination were evaluated from a modeled SLSC, and their values were compared with a multiple quantum well solar cell of the same aluminum composition. A discussion about the conditions, where SLSC performance overcomes that of a multiple quantum well solar cell, is addressed. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of residual copper selenide on CuInGaSe2 solar cells

Large-grain, copper-poor CuInGaSe₂ (CIGS) films are favored in the fabrication of highly efficient solar cells. However, the degradation of cell performance caused by residual copper selenide (Cu_2−xSe) remains a problem. This work studies the formation and behavior of excess Cu_xSe and further compares the cell performance of typical copper-poor with that of copper-rich solar cells. Since excess Cu_2−xSe cannot be exhausted during the growth, it fully surrounds the polycrystalline CIGS grains. Excess Cu_2−xSe in the CIGS film produces serious shunt paths and causes the pn junction to be of poor quality. A short circuit in copper-rich CIGS solar cells is attributable to the conductive Cu_2−xSe. The best way to ensure high-efficiency of the cells is to exhaust Cu_2−xSe during growth. Otherwise, a dense, chemically treated CIGS film is required to prevent the negative effects of excess Cu_2−xSe.     

Deposition of CuInSe2 films by a two-stage processutilizing E-beam evaporation

The deposition technique involves first depositing Cu and In metallic layers onto a substrate using the electron-beam evaporation method and then selenizing these layers in an H₂Se atmosphere. High-quality CuInSe₂ films of chalcopyrite phase have been obtained by this technique, and the films have been characterized by scanning electron microscopy, X-ray diffraction, electron microprobe, and resistivity measurements. Solar cells have been fabricated using these CuInSe₂ films, and active-area conversion efficiency values approaching 11% have been demonstrated for these devices     

Structure and properties of high efficiencyZnO/CdZnS/CuInGaSe2 solar cells

Thin-film polycrystalline solar cells with the structure ZnO/CdZnS/CuInGaSe₂ fabricated with total area efficiencies of up to 12.5% under AM1.5 equivalent illumination and 10.5% under AM0 equivalent are discussed. These are among the highest total area efficiencies reported for polycrystalline thin-film solar cells. Current-voltage and quantum efficiency data for such a high-efficiency cell are given. Described are the deposition of the CuInGaSe₂ by physical vapor deposition in vacuum, the CdZnS by chemical deposition from solution, and the ZnO by reactive sputtering. The electrical and optical properties of the individual layers have been inferred from measurements on complete devices and on separate witness layers. Optical constants and thicknesses obtained for the device layers from these measurements are presented, and the requirements for optimizing the device efficiency are discussed     

Simulation approach for optimization of ZnO/c-WSe2 heterojunction solar cells

Taking into account defect density in WSe₂, interface recombination between ZnO and WSe₂, we presented a simulation study of ZnO/crystalline WSe₂ heterojunction (HJ) solar cell using wxAMPS simulation software. The optimal conversion efficiency 39.07% for n-ZnO/p-c-WSe₂ HJ solar cell can be realized without considering the impact of defects. High defect density (> 1.0 × 10¹¹ cm^-2) in c-WSe₂ and large trap cross-section (> 1.0 × 10^-10 cm²) have serious impact on solar cell efficiency. A thin p-WSe₂ layer is intentionally inserted between ZnO layer and c-WSe₂ to investigate the effect of the interface recombination. The interface properties are very crucial to the performance of ZnO/c-WSe₂HJ solar cell. The affinity of ZnO value range between 3.7-4.5 eV gives the best conversion efficiency.     

N2 effect on GaAs etching at 150 mTorr capacitively-coupled Cl2/N2 plasma

The role of N₂ on GaAs etching at 150 mTorr capacitively-coupled Cl₂/N₂ plasma is reported. A catalytic effect of N₂ was found at 20-25% N₂ composition in the Cl₂/N₂ discharges. The peak intensities of the Cl₂/N₂ plasma were monitored with optical emission spectroscopy (OES). Both atomic Cl (725.66 nm) and atomic N (367.05 nm) were detected during the Cl₂/N₂ plasma etching. With the etch rate and OES results, we developed a simple model in order to explain the etch mechanism of GaAs in the high pressure capacitively-coupled Cl₂/N₂ plasma as a function of N₂ ratio. If the plasma chemistry condition became positive ion-deficient at low % N₂ or reactive chlorine-deficient at high % N₂ in the Cl₂/N₂ plasma, the GaAs etch rate is reduced. However, if the plasma had a more balanced ratio of Cl₂/N₂ (i.e. 20-25% N₂) in the plasma, much higher etch rates (up to 150 nm/min) than that in pure Cl₂ (50 nm/min) were produced due to synergetic effect of neutral chlorine adsorption and reaction, and positive ion bombardment. Pure Cl₂ etching produced 14 nm of RMS surface roughness of GaAs. Introduction of ?20% N₂ gas in Cl₂/N₂ discharges significantly reduced the surface roughness to 2-4 nm. SEM photos showed that the morphology of photoresist mask was strongly degraded. Etch rate of GaAs slightly increased from 10 to 40 nm/min when RIE chuck power changed from 10 to 150 W at 12 sccm Cl₂/8 sccm N₂ plasma condition. The surface roughness of GaAs etched at 12 sccm Cl₂/8 sccm N₂ plasma was 2-3 nm.