Design and numerical modeling of environmentally compatible HTL-free organic-inorganic perovskite solar cells

Abstract

Environment-friendly tin-based perovskite solar cells have gained much research interest because of the non-toxic nature of tin. The broader visible absorption spectrum of methylammonium tin iodide and smaller band-gap value of 1.3 eV have made methylammonium tin iodide viable to be used as an absorber layer in place of methylammonium lead iodide having toxic lead as its central element. Lead being water soluble is hazardous for the environment and human health, when a panel breaks or gets exposed to moisture. In this study, hole transport layer (HTL) free and lead-free, tin-based perovskite solar cell with layered structure as Glass/TCO/WS2/CH3NH3SnI3/back-contact, and its variant is proposed and investigated. To realize an optimum set of performance parameters, extensive investigations are carried out by considering two variants of the proposed design viz. lead-free absorber PSC (LF-PSC) and lead-free absorber optimized PSC (LFO-PSC). The impact of varying defect density and position of defects in bulk and at the interface on the performance of PSC is investigated and optimized. Changing defect density of the absorber layer shows a direct influence on diffusion length and the lifetime of charge carriers. Performance evaluation parameters of the LFO-PSC obtained in this study are Voc= 1.024 V, Jsc= 33.33 mA/cm2, FF= 80.13%, PCE= 27.33%. Higher efficiency is attributed to the presence of a single WS2/MASnI3 interface and therefore reduced recombination of charge carriers. PCE of optimized lead-free absorber PSC has been reported to be 8.9% higher than its basic variant i.e. LF-PSC design. The influence of defect levels, back reflecting coating and metal work function of back contact on the performance of PSC is investigated. Recombination curves are also studied to understand the impact of defects on the proposed PSC structure.