No abstract

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).

Aromatic ammonium salts have been regarded as the promising passivators in perovskite solar cell (PSC) fabrications. However, the complicated passivation procedure and inevitable formation of undesirable low‐dimensional (LD) perovskite layers limit further development. Furthermore, how the steric and electronic properties of different ammonium cations would influence the passivation is not well understood. Herein, two carefully engineered passivators based on the unique benzothiophene moiety involving the primary and secondary ammonium terminals, BTMA‐1 and BTMA‐2, respectively, are developed. It is shown that defects and, thus, nonradiative recombination reactions are effectively suppressed by simple posttreatments without the formation of LD perovskite. Interestingly, the champion efficiency of the BTMA‐2‐treated device increases to 23.10% from ≈20%, along with great stabilities and negligible hysteresis. An in‐depth understanding of the passivation effect influenced by steric and electronic properties is explored. The extra electron‐donating methyl on the ammonium nitrogen (BTMA‐2) increases the electron density on the N atom and the N–H+ ionic bond is, thus, boosted, which helps the positive terminal to anchor more tightly to the [PbI6]4− structure of the perovskite resulting in improved passivation effects. This novel and promising design strategy for ammonium passivators can promote PSCs to achieve further breakthroughs in both efficiency and stabilities.