Interface Engineering of Pb–Sn Low‐Bandgap Perovskite Solar Cells for Improved Efficiency and Stability

Because of their inferior film quality, Pb–Sn‐mixed low‐bandgap (LBG) perovskites suffer from poor charge transportation, compromising photovoltaic parameters of final solar cells. Herein, an approach to improve the quality of the charge interface layer is proposed, in which a thin layer of hydrophobic [bis (4‐phenyl) (2, 4, 6‐trimethylphenyl) amine] (PTAA) is inserted between the hole‐selective layer of hydrophilic poly (3, 4‐ethylenedioxythiophene) ‐polystyrenesulfonicacid (PEDOT:PSS) and LBG perovskite layer. The introduction of a tiny layer of the hydrophobic PTAA acts as a shield layer to protect the underlying acidic PEDOT:PSS layer from moisture‐related degradation and works as an intermediary layer to facilitate the growth of significantly larger perovskite grains; these enlarged grains are indicative of enhanced crystallinity and fewer grain boundaries in the perovskite layer. The fewer grain boundaries lead to suppression of interfacial defects and result in enhanced charge collection at the hole transport layer/perovskite interface, thus improving the open‐circuit voltage up to 0.85 V and fill factor up to ≈78%, eventually boosting the power conversion efficiency of the champion cell up to 19.08%. Herein, a simple interface engineering route to fabricate efficient and stable Pb–Sn‐mixed LBG perovskite solar cells is offered.