Challenges for Thermally Stable Spiro-MeOTAD toward the Market Entry of Highly Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) have drawn great attention because they have seen a dramatic increase in power conversion efficiency (PCE) over only a decade and reached 25.5% of certified PCE in 2021. The efficiency competitiveness with a low production cost puts up PSCs as a candidate for next-generation photovoltaics, encouraging the stability assessment. Research on PSCs, however, still struggles with the stability issue, particularly at elevated temperature, which is mainly ascribed to the use of spiro-MeOTAD as a hole transport material (HTM). Though many attempts have been made to explore a new HTM to replace spiro-MeOTAD, the improved stability is mostly obtained at the expense of losing efficiency. Likewise, the question of the effectiveness of alternatives for spiro-MeOTAD consistently remains. In this perspective, the morphological stability of spiro-MeOTAD at elevated temperatures is discussed to determine the underlying origins of the thermal stability issue and find feasible strategies to resolve it.