Solution-Processed SnOx as a Hole-Transporting Material for Stable Sn-Based Perovskite Solar Cell

Sn-perovskites are considered a suitable alternative to toxic Pb-perovskites due to their low toxicity and optimum optoelectronic properties. However, high-efficiency Sn-based perovskite solar cells (Sn-PSCs) typically use poly (3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) as a hole-transporting material (HTM), which limits their stability due to its acidic nature. This study introduces SnO_X nanocrystals, synthesized through a synproportionation reaction of Sn⁴⁺ with Sn⁰ under mild conditions, as a replacement for PEDOT:PSS. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy analyses revealed that the Sn⁰ reduces Sn⁴⁺ by 38% and elevates the highest occupied molecular orbital to –5.70 eV, close to PEDOT:PSS, enabling HTM behavior. The perovskite films on SnO_X exhibit improved grain size and crystallinity compared to PEDOT:PSS. The resulting SnO_X-based Sn-PSCs achieved a power conversion efficiency of 11.11%. They retained 90% of their efficiency after 1000 h of maximum power point tracking, indicating superior stability over PEDOT:PSS-based devices.