Hybrid perovskite solar cells (PSC) have achieved efficiencies (PCE) of more than 25%. However, the organic compound is causing structural degradation due to heat and moisture. This has led to the exploration of inorganic perovskites. Inorganic-PSC such as cesium has seen a breakthrough by achieving highly stable PSC with PCE exceeding 15%. In this work, the inorganic non-toxic PSC of cesium germanium tri-iodide (CsGeI₃) is numerically modeled in SCAPS-1D with two carbon-based and two copper-based charge transport layers(CTL). This study introduces in-depth modelling and analysis of CsGeI₃ through continuity and Poisson equations. Cu-CTL are selected to increase the electric conductivity of the cell, while carbon-CTL is used to increase the thermal conductivity. Four structures are designed and presented. A systematic approach is adopted to obtain the optimized design parameters for maximum performance. From the results it is observed that the C₆₀/CsGeI₃/CuSCN structure has the highest performance, with open-circuit voltage of 1.0169V, short-circuit current of 19.653 mA/Cm², fill factor of 88.13% and PCE of 17.61%. Moreover, the effect of quantum efficiency, electric field, interface recombination, interface defects, layer thickness, defect density, doping concentration, working temperature and reflection coating on the cell performance are studied in detail.

The different material layers were first numerically modelled individually in SCAPS-1D software. The layers included 1 Perovskite absorber layer (CsGeI₃), 2 hole transport layers (CuSCN & CuSbS₂) 2 electron transport layers (PCBM & C₆₀). From the combination of the different layers, four perovskite solar cell structures were modelled. The defect density was modelled inside each layer and interface defects were modelled between the layers. The IV characteristics, energy band alignment, quantum efficiency, electric field and recombination were calculated through continuity and Poisson equations (SCAPS). The standard test condition (STC) was used to collect data from each structure. After that, the effect of layer thickness and doping concentration on the cells' performance was analysed by varying the thickness and doping in each layer with equal increments. The open circuit voltage, short circuit current, fill factor and power conversion efficiency were recorded for each increment. The optimized value (Saturation point) was identified for each parameter. In the end the effect of defect density, interface defect and working temperature on the cells' performance (efficieny) was checked by increasing each parameter individually.

SCAPS-1D software is reduired to open the numerically modelled layers.

Microsoft Excel is required to open the collected data/results.