The open-circuit voltage of back-surface-field (BSF) p-n junction solar cells in concentrated sunlight

Simple analytical expressions for the open-circuit voltage of the n⁺?p?p⁺ and p⁺?n?n⁺ BSF solar cells, which are valid for both the low- and high-levels of optical illumination, are derived. Based on the principle of superposition the open-circuit voltage of both the n⁺?p?p⁺ and p⁺?n?n⁺ solar cells are expressed in terms of the short-circuit current and the known saturated dark current. Effects of the high-low junction doping, the energy-gap shrinkage, and the dimensions of the BSF solar cells on the open-circuit voltage are included. The numerical results of the derived expressions are found to be in good agreement with the exact numerical analysis of Fossum et al. The optimal design considerations based on the known characteristics of the open-circuit voltage are also discussed.     

Physics and technologies of superhigh-efficiency tandem solar cells

The present status of superhigh-efficiency tandem solar cells has been reviewed and the key issues for realizing superhigh-efficiency have been discussed. The mechanical, stacked, three-junction cells of monolithically grown InGaP/GaAs two-junction cells and InGaAs cells have reached the highest efficiency (attainable in Japan) of 33.3% at 1-sun AM 1.5. Future prospects for realizing superhigh-efficiency and low-cost tandem solar cells are discussed. Fiz. Tekh. Poluprovodn. 33, 1054–1058 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Improved performance thin solar cells

A silicon solar cell device structure was developed to improve performance from thin cells. The design has collecting junctions both on the illuminated and most of the dark sides. Since the two junctions function interdependently, the device is called a tandem junction cell (TJC). The photoresponseI-Vperformance of cells was measured in two modes, with either collection from the junctions on both sides, or collection from only the nonilluminated side. Efficient current collection from TJC cells was observed in both modes, and current collection improved as the cell thickness was reduced. At the calculated optimum thickness of 30-50 µm, collection for the two modes should be equivalent.     

Physics of BSF solar cells at high levels of illumination

The theory of BSF solar cells by Fossum et al. [1] is extended to high levels of injection. For such intensities, more generalJ_{SC}-V_{OC}relationships are derived which show deviation from the idealexp (qV/kT)relationship.     

Fundamental electronic mechanisms limiting the performance of solar cells

The efficiency of a solar cell depends on the electronic parameters which characterize the transport, recombination, and generation of electrons and holes in semiconductors. This paper describes the many basic mechanisms that can control these electronic parameters in solar cell materials.     

F-containing cations improve the performance of perovskite solar cells

Organic–inorganic halide perovskite solar cells(PSCs)have delivered power conversion efficiency(PCE)on par with that of crystalline silicon solar cells,due to the considerable effort on the optimization of perovskite materials and devices[1].The three-dimensional(3D)perovskite-based PSCs with the standard n–i–p architecture gave a certified PCE of25.5%[2].However,the poor device stability under operating conditions remains an obstacle to commercialization.The 3D hybrid perovskite materials are susceptible to oxygen,UV light,humidity,heat,and electric fields[3].To improve device stability,two main strategies are applied:(1)improving the intrinsic stability[4];(2)providing sufficient protection.     

Reduction of solar cell efficiency by edge defects across the back-surface-field junction:— A developed perimeter model

Material imperfections, impurity clusters and fabrication defects across the back-surface-field junction can degrade the performance of high-efficiency solar cells. The degradation from defects appearing on the circumference of a solar cell is analyzed using a two-region developed perimeter device model. The width of the defective perimeter region is characterized by the range or the distance-of-influence of the defective edge and this width is about two diffusion lengths. The defective edge is characterized by a surface recombination velocity. Family of theoretical curves and numerical examples are presented to show that significant reduction of open-circuit voltage can occur in high-efficiency cells which are thin compared with the diffusion length. In one example, the degradation is decreased from 135 mV to 75 mV when the cell size is increased from 10 to 100 times the diffusion length in a thin cell whose thickness is 1% of the diffusion length.     

Screening solar cells for improved array performance

Solar cells are produced in batches and undergo a screening process, usually based on the maximum power point. The manufacturer or consumer aggregates the solar cells randomly to form an array. By screening the solar cells and aggregating in a ranking order we may obtain improved array performance. In the present study we investigate several screening criteria of a batch of solar cells and rank them in an order. We also investigate several array topologies constructed by the screened solar cells and compare the results with arrays of randomly selected cells. In terrestrial applications, panels usually form the array. In this case the panel may be viewed as the basic unit for the screening. The results of the study show that improved array performance may be obtained for screened solar cells as opposed to randomly selected cells if part of the solar cells in the batch is used to form the array. If allthe cells are used, no noticeable improvement is seen. For a sufficiently tight manufacturing tolerance there is no need to screen the solar cells. Copyright © 1999 John Wiley & Sons, Ltd.     

Effects of defect states on the performance of perovskite solar cells

We built an ideal perovskite solar cell model and investigated the effects of defect states on the solar cell''s performance. The verities of defect states with a different energy level in the band gap and those in the absorption layer CH₃NH₃PbI₃ (MAPbI₃), the interface between the buffer layer/MAPbI₃, and the interface between the hole transport material (HTM) and MAPbI₃, were studied. We have quantitatively analyzed these effects on perovskite solar cells'' performance parameters. They are open-circuit voltage, short-circuit current, fill factor, and photoelectric conversion efficiency. We found that the performances of perovskite solar cells change worse with defect state density increasing, but when defect state density is lower than 10¹⁶ cm^-3, the effects are small. Defect states in the absorption layer have much larger effects than those in the adjacent interface layers. The perovskite solar cells have better performance as its working temperature is reduced. When the thickness of MAPbI₃ is about 0.3 μm, perovskite solar cells show better comprehensive performance, while the thickness 0.05 μm for Spiro-OMeTAD is enough.     

等离子体刻蚀对CdTe太阳电池性能的影响

采用不同干法腐蚀条件下的CdTe薄膜制成器件, 通过I-V、C-V和光谱响应等测试 了电池性能参数。结果表明,溅 射时间太短和功率太小时不能完全去除氧化层,溅射时间过长和功率过高会对薄膜表面造成 损伤, 影响器件性能。 通 过选择器件性能较好的电池、 找出适合等离子束溅 射工艺的条件,所制成的电池转化效率 达 到10.99%;而湿法腐蚀所 制成器件的转化效率为 10.26%。由此可以认为,等离子束轰击溅射的 腐蚀方法较湿法腐蚀更适用于CdTe太阳电池的制备。     

Influence of GaInP ordering on the performance of GaInP solar cells

CuPt-type ordering with undesirable properties always occurs in GaInP at growth conditions that are very close to those leading to the highest quality material in metal organic chemical vapor deposition. In this work, highly disordered GaInP with high crystalline quality was obtained by optimizing growth conditions. Room-temperature and low-temperature photoluminescence (PL) spectra of AlGaInP/GaInP/AlGaInP double heterostructures (DHs) reveal that the band edge emission intensity is enhanced by optimizing growth temperature, V/III ratio, and reactor pressure at the expense of low energy peak originating from spatially indirect recombination due to the ordering-related defects. The DH sample with less ordering-related defects demonstrates a longer effective minority carrier lifetime, consequently, the GaInP solar cell shows a significant improvement in the performance.     

Effect of MoSe2 on the performance of CIGS solar cells

A CuIn1-xGaxSe2 (CIGS) thin film solar cell model with MoSe2 transition layer was established, using SCAPS-1D software. The influence of MoSe2 interface layer formed between absorption layer CIGS and the back contact Mo on the solar cell performance was investigated.By changing the doping concentration,thickness and bandgap of MoSe2 layer, it is found that the MoSe2 and the variation of parameters have a significant effect on the electrical characteristics and photovoltaic parameters of CIGS thin film solar cells. Based on the energy band, the interfaces of Mo/MoSe2 and MoSe2/CIGS are analyzed. It is considered that Mo/MoSe2 is a Schottky contact, MoSe2/CIGS is an ohmic contact. When suitable parameters of MoSe2 layer are formed into the interface, it will provide a new path for designing CIGS solar cells with thinner absorption layer.     

Influence of metal-covered area on performance of solar cells

Analytical expressions are proposed showing that the efficiency and fill factor of solar cells depend on the three normalised parameters rm, rL and g. These expressions are obtained with a new theoretical model, representing the metal-covered area of the solar cell.     

Al-doping effects on the photovoltaic performance of inverted polymer solar cells

The properties of Al-doped ZnO (AZO) play an important role in the photovoltaic performance of inverted polymer solar cells (PSCs), which is used as electron transport and hole blocking buffer layers. In this work, we study the effects of Al-doping level in AZO on device performance in detail. Results indicate that the device performance intensely depends on the Al-doping level. The AZO thin films with Al-doping atomic percentage of 1.0% possess the best conductivity. The resulting solar cells show the enhanced short current density and the fill factor (FF) simultaneously, and the power conversion efficiency (PCE) is improved by 74%, which are attributed to the reduced carrier recombination and the optimized charge transport and extraction between AZO and the active layer.     

Enhancing the performance of porphyrin based solar cells by the Bipy coordination

Solution processed organic solar cells (OSCs) often suffer from low charge mobilities partially due to the disordered non-crystalline or amorphous morphology of their films. In this study, 4,4′-bipyridyl (Bipy) is introduced to coordinate a zinc(II) porphyrin to form porphyrin complexes. A significant enhanced hole mobility and solar cell device performance are attained when the ratio of Bipy is 0.25 in blend films with [6, 6]-phenyl C₆₁-butyric acid methyl ester (PC₆₁BM). When [6, 6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) was used instead of PC₆₁BM, the PCE is enhanced to 2.83% in the presence of 0.25 equiv Bipy, which is an increase of 53% compared to that without Bipy.     

Influence of the layer parameters on the performance of the CdTe solar cells

Influence of the layer parameters on the performances of the CdTe solar cells is analyzed by SCAPS-1D. The ZnO:Al film shows a high efficiency than SnO2:F. Moreover, the thinner window layer and lower defect density of CdS films are the factor in the enhancement of the short-circuit current density. As well, to increase the open-circuit voltage, the responsible factors are low defect density of the absorbing layer CdTe and high metal work function. For the low cost of cell production, ultrathin film CdTe cells are used with a back surface field (BSF) between CdTe and back contact, such as PbTe. Further, the simulation results show that the conversion efficiency of 19.28% can be obtained for the cell with 1-μm-thick CdTe, 0.1-μm-thick PbTe and 30-nm-thick CdS.     

The effect of crystal defects on the performance of gaas solar cells

The nature and the effect of crystal defects on the performance of GaAs/GaAlAs solar cells fabricated by MOCVD production reactors have been evaluated. Intrinsic threading dislocations from the GaAs substrates propagate through the junction and are believed to act as recombination centers reducing both the short circuit current density and the open circuit voltage of the device. These defects, at a concentration level exceeding 2 × 10⁴ cm⁻², detrimentally affect the electrical performance of the solar cells.     

Influence of bandgap narrowing on the performance of silicon n-p solar cells

This paper deals with the incorporation of bandgap narrowing in the modelling of n⁺-p solar cells. First, the physcial model on which the computations are based, is explained. Second, the technology used to fabricate the solar cells, and the measurement technique for the minority carrier lifetime are commented. Then a detailed comparison between measured and computed results of I_sc, V_oc and P_max follows and the importance of inclusion I72 of the bandgap narrowing is illustrated. The theoretical case where Auger—recombination is the only recombination process is also treated. Finally computed results obtained for solar cells with different surface concentrations are shown.