Upgrading Spiro-OMeTAD with β-Chloroethylcarbazole to Improve the Stability of Perovskite Solar Cells

Spiro-OMeTAD has served as a crucial hole transporting material (HTM) in the advancement of efficient perovskite solar cells (PSCs). However, the diminished thermal stability of lithium-doped Spiro-OMeTAD (Li-Spiro) has been a limiting factor, leading to a significant decline of the power conversion efficiency (PCE) and stability, particularly at a temperature exceeding 65 °C. Here, we report an upgraded HTM, Spiro-OMeCzCl, by incorporating chloroethyl-modified carbazole units to expand the conjugated area of the donor group. This novel configuration significantly enhances the thermal stability and film quality. The resulting PSCs utilizing Spiro-OMeCzCl achieved a high PCE of 24.6%, coupled with exceptional long-term stability. The target cells maintained approximately 95% of their initial PCE after 57 days under a nitrogen atmosphere. Importantly, in subsequent thermal stability tests involving a gradual temperature increase, the cells sustained an average PCE of over 85% after 200 h at temperatures ranging from 60 to 90 °C.