Improving the Long-Term Stability of Doped Spiro-Type Hole-Transporting Materials in Planar Perovskite Solar Cells

The improvement of the long-term stability of perovskite-based solar cells (PSCs) toward commercialization is closely linked to the development of cutting-edge charge-transporting materials. The progress on the design and the synthesis of new hole-transporting materials (HTMs) is synergistically attaining both top efficiencies and promising stability. Herein, the synthesis and characterization of two doped-HTMs based on electron-rich spiranic cores, namely, 9H-quinolinophenoxazine (spiro-POZ) and 9H-quinolinophenothiazine (spiro-PTZ), are presented. The novel HTMs exhibit excellent solubility, optimal highest occupied molecular orbital energy, and excellent thermal stability with glass transition temperatures higher than those for spiro-OMeTAD. [(FAPbI(3))(0.87)(MAPbBr(3))(0.13)](0.92)[CsPbI3](0.08)-based solar cells using the new spiro-type HTMs deliver power conversion efficiencies (PCEs) around 17% for mesoporous cells, and higher than 18% in planar configurations, matching the PCE of spiro-OMeTAD. Remarkably, doped spiro-POZ and spiro-PTZ exhibit excellent long-term stability in planar devices, retaining over 84% of their initial efficiency after more than 300 days of exposure to ambient conditions. Furthermore, after 1200 h under continuous 1 sun illumination, the PCE of the PSCs based on spiro-POZ and spiro-PTZ decreases by only 6%.