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, 9 H ‐quinolinophenoxazine ( spiro‐POZ ) and 9 H ‐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 [CsPbI 3 ] 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%.