Passivation and Charge Carrier Selectivity Optimization for Narrow Bandgap Perovskite Solar Cells

This study aims to enhance narrow bandgap perovskite solar cells for all-perovskite tandem applications. Initial efforts focused on bulk passivation of the perovskite layer. The combination of two additives, Methylammonium chloride and Lead thiocyanate, increased Voc up to 0.82V and Jsc to 31mA/cm^2. Glycine hydrochloride improved result reproducibility leading to a favourable FF, and increasing Thiourea concentration simultaneously raised Jsc. Further optimizations and the effects of additive combinations will be presented. Concurrently, this study investigates the selectivity of the hole transport layer/perovskite interface. Thus, we examined substituting an aqueous PEDOT:PSS formulation for a solvent-based one to address water-induced degradations in the underlying perovskite layer in all-perovskite tandem devices. Preliminary assessments on single-junction narrow bandgap solar cells using solvent-based PEDOT yielded a notable 16% Voc increase compared to aqueous PEDOT:PSS. However, this rise in Voc results in a significant 23% Jsc reduction. In response, we explored strategies to boost Jsc by varying the PEDOT thickness. In thinner layers, Jsc exceeds the one of PEDOT:PSS-based cells, aligning with simulations. This research outcome provides valuable insights into optimizing passivation and enhancing selectivity in narrow bandgap perovskite solar cells.