Cyano-4′-Pentylbipheny dopant strategy for P3HT-Based CsPbI3 perovskite solar cells with a record efficiency and preeminent stability

Poly(3-hexylthiophene) (P3HT) as hole transport layer (HTL) had been used in inorganic cesium lead triiodide (CsPbI3) perovskites solar cells (PSCs) due to its excellent hydrophobic property and cheap cost. However, its relatively low hole mobility and mismatched energy level with CsPbI3 perovskite led to large losses in fill factor (FF) and open-circuit voltage (Voc), and thus impair the photovoltaic performance of CsPbI3 PSCs. Herein, we successfully increase the hole mobility of P3HT by incorporating a nematic liquid crystal molecule 4-Cyano-4-Pentylbipheny (5CB) on account of the formation of face-on orientation and the improvement of π-π stacking of P3HT. Meanwhile, the defect density was reduced and the energy level arrangement was also optimized at CsPbI3/P3HT interface by 5CB dopant. As a result, the more balanced hole/electron mobility and suppressed non-radiative recombination are achieved, and thus Voc and FF were significantly increased. A record high-efficiency of 18.75% was obtained for P3HT-based CsPbI3 PSCs. Noteworthy, the unencapsulated CsPbI3 PSCs with P3HT:5CB HTL also shows superior moisture stability by maintaining 90% of initial PCE in ambient air with 15–30 % RH for 500 h. Our work reveals that 5CB dopant is a comprehensive strategy for improving efficiency and stability of P3HT-based PSCs.