Harnessing the potential of lead-free Sn–Ge based perovskite solar cells by unlocking the recombination channels

Perovskite solar cells (PSCs) have celebrated a decade of investigation as a promising photovoltaic technology. However, they contain lead, so inorganic lead-free PSCs can be designed as green and clean energy sources. To overcome the current obstacles in lead-free PSCs, the stability and performance gap should be minimized. The drift-diffusion simulation model is a conducive way to understand the working mechanism in a thin-film solar cell. Here we adopted a computational approach to design and investigate the performance of CsSn0.5Ge0.5I3 as a light harvester. We optimize the thickness of the perovskite, for its use in an inverted planar structure (FTO/PCBM/CsSn0.5Ge0.5I3/Spiro-OMeTAD/Au). Furthermore, cerium oxide (CeOx) and PTAA are used as alternative electron and hole transport layers, respectively. We studied the effect of trap density in the bulk CsSn0.5Ge0.5I3 and its impact on performance, recombination rate, and diffusion length. The open-circuit voltage (Voc) showed a significant improvement and the correlation with the trap density at the interface layers is established. We noted that the defect density at the perovskite/hole selective layer interface has a profound impact on the performance of lead-free PSCs as compared to the electron selective layer/perovskite interface. After optimizing defect parameters, the lead-free PSC can deliver a PCE of 24.20%, with Voc = 1170 mV, Jsc = 25.80 mA cm−2, and FF = 80.33%. Our findings provide access guidelines and pave the way for lead-free PSCs based on the Sn–Ge combination to approach their limit.