Abstract
Abstract
Lead-free tin halide perovskites for the fabrication of perovskite solar cells have attracted considerable attention due to their outstanding optoelectronic and ecofriendly properties. These materials face severe issues, such as poor environmental stability, low formation energy and faster oxidation of tin from the Sn2+ to Sn4+ state, leading to poor film quality and self-doping. In this work, we have fabricated FA0.75MA0.25SnI3 perovskite thin films via a solution processing method and studied the conjugated polymer poly [N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadia-zole)] (PCDTBT)-induced effects in perovskite thin films. The micro-strain of PCDTBT-doped FA0.75MA0.25SnI3 perovskite reduced without any change in the crystal structure. Reductions in electron trap density have been observed due to improved film quality and enlarged perovskite grains. We have observed that the Sn4+ content in 0.050 wt% PCDTBT-doped FA0.75MA0.25SnI3 perovskite film gets reduced, as shown in the x-ray photoelectron spectroscopy (XPS) results. The reduction in Sn4+ (cause of self-doping) content shows that PCDTBT doping maintains the stability of Sn2+ in FA0.75MA0.25SnI3 perovskite thin film. A decrement in hole density from 3.2 × 1018 cm−3 for pristine films to 1.3 × 1017cm−3 for 0.050 wt% PCDTBT-doped FA0.75MA0.25SnI3 perovskite has been observed from C–V measurement, which is consistent with the XPS results. Thus, PCDTBT doping in perovskite films can effectively tackle the severe issues of tin oxidation and defects in the lead-free tin halide perovskite photoactive layer for solar cell application.