Fine-tuning chemical passivation over photovoltaic perovskites by varying the symmetry of bidentate acceptor in D–A molecules

Abstract

To pursue the efficient photovoltaic performance of perovskite solar cells (PSCs), a series of passivators have been employed to cure the defects of perovskite. A feasible strategy for designing efficient passivators is enhancing strong passivation capacity for effectively coordinating with under-coordinated Pb²⁺ on the surface of the perovskite. In this work, the TA-MN passivator with a symmetric bidentate acceptor can achieve the synergistic passivating effect of two symmetric cyano groups (CN) and thus exhibited an excellent passivation ability over the single passivating effect of carboxyl (COOH) or CN group in TA-CA passivator with the asymmetric bidentate acceptor, which is attributed to the fact that the same electron-withdrawing ability can promote the same CN groups in symmetric bidentate acceptor obtain similar electron density and thus interact together with under-coordinated Pb²⁺ simultaneously. Moreover, a better band alignment with a hole-transporting layer (HTL) can be achieved by the perovskite films with a TA-MN passivator. These results promote TA-MN-based PSCs to obtain a higher PCE of 21.19% with V_OC of 1.114 V, J_SC of 24.60 mA cm⁻² and fill factor (FF) of 77.37%, which is larger than that of TA-CA (20.54%) and control (19.49%). Furthermore, 1 cm² scaling-up preparation and good stability of TA-MN-based PSCs were also further confirmed to be practical. This work provides a more effective design of passivators with symmetric bidentate acceptors for strong synergistic passivating ability.