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It is common practice in the lead halide perovskite solar cell field to add a small molar excess of lead iodide (PbI2) to the precursor solution to increase the device performance. However, recent reports have shown that an excess of PbI2 can accelerate performance loss. In addition, PbI2 is photoactive (band gap ∼2.3 eV), which may lead to parasitic absorption losses in a solar cell. Here we show that devices using small quantities of excess PbI2 exhibit better device performance as compared with stoichiometric devices, both initially and for the duration of a stability test under operating conditions, primarily by enhancing the charge extraction. However, the photolysis of PbI2 negates the beneficial effect on charge extraction by leaving voids in the perovskite film and introduces trap states that are detrimental for device performance. We propose that although excess PbI2 provides a good template for enhanced performance, the community must continue to seek other additives or synthesis routes that fulfill the same beneficial role as excess PbI2, but without the photolysis that negates these beneficial effects under long-term device operation.

In this work a lead free perovskite solar cell structure is proposed with NiO as the hole transport material (HTM), CH3NH3SnI3 as the perovskite absorber material and PCBM (phenyl C61 butyric acid methyl ester) as the electron transport material (ETM). Numerical analysis of the designed solar cell is performed using Solar Cell Capacitance Simulator (SCAPS-1D) program. The power conversion efficiency (PCE) of the optimized device stack is found to be above 29% with Voc = 0.98 V, Jsc = 34.86 mA/cm2, FF = 85.64%. The lead free perovskite solar cell with different HTM and ETM may be investigated for high PCE.

In this work the one dimensional device simulation of lead-free perovskite solar cell of CH 3 NH 3 SnI 3 absorber perovskite material is performed. The parameters which affect the overall performance of the solar cell are investigated and it is observed that the absorber thickness, doping concentrations of HTM (hole transport material), ETM (electron transport material) and perovskite absorber and temperature, influence the solar cell performance. The optimized performance of the perovskite solar cells with PCE (power conversion efficiency) of 30.59%, is obtained when the thicknesses of perovskite was 300nm and the doping concentrations of Cu2O, PCBM and perovskite were 9×10 21 cm- 3 , 1×10 21 cm -3 and 1×10 13 cm -3 respectively. It is observed that suitable optimization of material parameters and device dimensions may lead to high efficiency Perovskite solar cell.

Multi-junction solar cells based on III-V materials are widely utilized for space applications owing to their light weight and very high efficiency. When used for terrestrial applications, they are used in concentrator systems to boost the efficiency and reduce the effective solar cell area to enhance the performance-to-cost ratio. However, the efficiency drops as the light intensity goes beyond a certain value mainly because of the sharp drop in fill factor. In this study, InP and InGaP were designed to be the bottom and top cell absorbers for multi-junction architecture. Effects of variation of Ga mole fraction in InGaP and the top cell absorber thickness on the overall electrical performance of the solar cell were simulated in SILVACO TCAD software. When used in the concentrator conditions, the maximum efficiency of 28.4076% was obtained under 2 suns and efficiency was found to drop drastically at higher intensities.