Hysteresis-Less CsPbI₂Br Mesoscopic Perovskite Solar Cells with a High Open-Circuit Voltage Exceeding 1.3 V and 14.86% of Power Conversion Efficiency

High-performance and hysteresis-less mesoscopic CsPbI2Br perovskite solar cells (PSCs) are demonstrated by adapting hole-transporting materials (HTMs) with controlled highest occupied molecular orbital (HOMO) values. The used model HTMs are poly-3-hexylthiophene (P3HT), poly-triarylamine (P-TAA), poly-fluoren-8-triarylamine (PF8-TAA), and poly-indenofluoren-8-triarylamine (PIF8-TAA), and their HOMO energy levels position to −4.98, −5.09, −5.45, and −5.52 eV, respectively. By controlling the HOMO of the HTMs, the average open-circuit voltages of 25 mesoscopic CsPbI2Br PSCs are controllable from 1.11 ± 0.030 V for a P3HT HTM-based device to 1.17 ± 0.023, 1.21 ± 0.027, and 1.27 ± 0.028 V for P-TAA, PF8-TAA, and PIF8-TAA HTM-based devices. As a result, the PIF8-TAA HTM-based mesoscopic PSC exhibits the highest open-circuit voltage of 1.31 V and power conversion efficiency (PCE) of 14.20% for the forward scan condition and 14.86% for the reverse scan condition under 1 sun illumination (100 mW/cm2 AM 1.5G). In addition, the unencapsulated mesoscopic CsPbI2Br PSCs exhibited 10–14% of PCE degradation compared to their initial efficiency in maximum power point tracking under continuous 1 sun light soaking at 85 °C for 1000 h.