Decorating hole transport material with −CF3 groups for highly efficient and stable perovskite solar cells

The hole transport material (HTM) plays an extremely important role to determine the power conversion efficiency (PCE) and the stability of perovskite solar cells (PSCs). Herein, we report an effective strategy to improve the performance of HTMs by introducing −CF3 groups via the rational decorative mode. Upon direct attachment or nonconjugated alkoxyl bridging of −CF3 groups on the terminal diphenylamines, the resulting molecular HTMs, i.e., 2,7-BCzA4CF3 and 2,7-BCzA4OCCF3, show distinct properties. Compared with 2,7-BCzA4CF3, the nonconjugated alkoxyl bridging −CF3 group-based 2,7-BCzA4OCCF3 exhibits better thermal stability, hydrophobicity, and a dramatically upgraded hole mobility by 135.7-fold of magnitude to 1.71 × 10−4 cm2 V−1 S−1. The PSCs with 2,7-BCzA4OCCF3 as HTM exhibit an PCE of up to 20.53% and excellent long-term stability, maintaining 92.57% of their performance for 30 days in air with humidity of 30% without encapsulation. This work provides beneficial guidelines for the design of new HTMs for efficient and stable PSCs.