Thickness dependent numerical investigations of lead free perovskite/CIGS bilayer solar cell using SCAPS-1D

Due to the toxicity and the complex fabrication process lead-based perovskite solar cells are difficult to fabricate commercially though the power conversion efficiency has reached 25.2 ​%. In the current scenario, lead free perovskite solar cell devices are gaining interest among the researchers and the bilayer structure is showing significant improvement in the efficiency. In this work, with the help of SCAPS 1D, a lead free single-layer perovskite (CH₃NH₃SnBr₃) solar cell and a bilayer structure (CH₃NH₃SnBr₃/CIGS) have been investigated to compare the photovoltaic performance by using PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and SnTe as an electron transport layer (ETL) and hole transport layer (HTL) respectively. Different device parameters i.e. thickness, defect density, doping concentration and series-shunt resistance of the device was optimized to obtain the best performance. In the case of a single absorber layer, power conversion efficiency (PCE), open circuit voltage ($V_{\text{oc}})$, fill factor (FF) and the short circuit current density $\left(J_{\text{sc}}\right)$ were achieved 20.58 ​%, 0.931 ​V, 64.95 ​% and 34.03 ${\text{mA}.\text{cm}}^{-2}$ respectively. However, it is observed that bilayer structure (FTO/PCBM/CH₃NH₃SnBr₃/CIGS/ZnTe/SnTe/Au) obtains 22.68 ​% of PCE, 0.916 ​V of $V_{\text{oc}}$, 71.46 ​% of FF and 34.66 ${\text{mA}.\text{cm}}^{-2}$ of $J_{\text{sc}}$. This study suggests that a proper bilayer structure is beneficial to improve the device performance in terms of J_sc and FF by increasing the carrier generation and reducing the back surface field recombination.