Nitrogen-doped titanium dioxide as a novel eco-friendly hole transport layer in lead-free CsSnI3 based perovskite solar cells

Abstract Despite recent abrupt rise in the efficiency of perovskite solar cells (PSCs), the contact layers maybe limit the efficiency of PSCs. The hole transporting layer (HTL) is an essential layer for reducing the recombination and loosing charges in fabricated devices by avoiding direct contact of gold to perovskite absorber layer in an efficient PSC device. The pristine spiro-OMeTAD, as most widely used HTL, still suffers from poor electrical conductivity, low hole mobility, and low oxidation rate. In this research, the nitrogen doped TiO₂ (N-TiO₂) proposed as a low-cost, efficient, safe replacement for spiro-OMeTAD HTL in PSCs. The variation in the device design key parameters such as the thickness and bulk defect density of perovskite layer, simultaneous modifications of defect density and defect energy level, and acceptor doping concentration in absorber layer are examined with their impact on the photovoltaic characteristic parameters. The effect of an increase in operating temperature from 280 K to 460 K on the performance of CsSnI₃-based perovskite devices is also investigated. The standard simulated lead-free CsSnI₃–based PSCs with spiro-OMeTAD HTL by SCAPS-1D software revealed the highest power conservation efficiency (PCE) of 23.63%. The CsSnI₃-based solar cell with N-TiO₂ as HTL showed FF (79.65%), V_OC (0.98 V), J_sc (34.69 mA/cm²), and efficiency (27.03%) higher than the standard device with conventional spiro-OMeTAD HTL. The outcomes of N-TiO₂ presence as an HTL signify a critical avenue for the possibility of fabricating high PCE CsSnI₃-based perovskite devices made of stable, low-cost, efficient, safe, and eco-friendly materials.