Efficient wide-bandgap perovskite solar cells with open-circuit voltage deficit below 0.4 V via hole-selective interface engineering

Wide-bandgap mixed-halide perovskite solar cells (WBG-PSCs) are promising top cells for efficient tandem photovoltaics to achieve high power conversion efficiency (PCE) at low cost. However, the open-circuit voltage (V-OC) of WBG-PSCs is still unsatisfactory as the V-OC-deficit is generally larger than 0.45 V. Herein, we report a buried interface engineering strategy that substantially improves the V-OC of WBG-PSCs by inserting amphophilic molecular hole-selective materials featuring with a cyanovinyl phosphonic acid (CPA) anchoring group between the perovskite and substrate. The assembly and redistribution of CPA-based amphiphilic molecules at the perovskite-substrate buried interface not only promotes the growth of a low-defect crystalline perovskite thin film, but also suppresses the photo-induced halide phase separation. The energy level alignment between wide-bandgap perovskite and the hole-selective layer is further improved by modulating the substituents on the triphenylamine donor moiety (methoxyls for MPA-CPA, methyls for MePA-CPA, and bare TPA-CPA). Using a 1.68 eV bandgap perovskite, the MePA-CPA-based devices achieved an unprecedentedly high V-OC of 1.29 V and PCE of 22.3% under standard AM 1.5 sunlight. The V-OC-deficit (<0.40 V) is the lowest value reported for WBG-PSCs. This work not only provides an effective approach to decreasing the V-OC-deficit of WBG-PSCs, but also confirms the importance of energy level alignment at the charge-selective layers in PSCs.