Reduced VOC Deficit of Mixed Lead–Tin Perovskite Solar Cells via Strain‐Releasing and Synergistic Passivation Additives

The power conversion efficiency (PCE) of tin-lead perovskite solar cells (PSCs) is normally lower than that of Pb cells, mainly due to greater open circuit voltage (VOC ) losses. Herein, the additive 2,6-diaminopyridine (TNPD) is designed to anchor on the surface of the perovskite precursor colloid as nucleating agent to modulate the growth of Pb-Sn perovskites. It is observed that the TNPD not only effectively induces crystal growth during the nucleation stage, remaining on the crystal surface and ultimately passivating the resulting perovskite films, but also releases the micro-strain generated during the film growth. Furthermore, TNPD could lower the defect density (Sn4+ amount) by screening the perovskite against oxygen and by synergistically bonding with undercoordinated Sn/Pb on the surface. Finally, a high VOC of 0.85 V is obtained, corresponding to a voltage deficit of 0.41 V using a perovskite absorber with a bandgap of 1.26 eV, and a high PCE (20.35%) reported so far for Pb-Sn PSCs. Moreover, the stability of the TNPD-incorporated device is significantly improved, and the PCE maintains 50% of the initial value after about 1000 h storage in glovebox without encapsulated, in comparison to that of the control device (about 700 h, maintaining 30% of the initial value).