23.2% Efficient Low Band Gap Perovskite Solar Cells with Cyanogen Management

Managing iodine formation is crucial for realising efficient and stable perovskite photovoltaics. Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) is a widely adopted hole transport material, particularly for perovskite solar cells (PSCs). However, improving the performance and stability of PEDOT:PSS based perovskite optoelectronics remains a key challenge. We show that amine-containing organic cations de-dope PEDOT:PSS, causing performance loss, which is partially recovered with thiocyanate additives. However, this comes at the expense of device stability due to cyanogen formation from thiocyanate-iodine interaction which is accelerated in the presence of moisture. To mitigate this degradation pathway, we incorporate an iodine reductant in lead-tin PSCs. The resulting devices show an improved power conversion efficiency of 23.2% which is among the highest reported for lead-tin PSCs, and ~66% enhancement in the TS80 lifetime under maximum power point tracking and ambient conditions. These findings offer insights for designing next-generation hole extraction materials for more efficient and stable PSCs.