Small Molecules Functionalized Zinc Oxide Interlayers for High Performance Low-Temperature Carbon-Based CsPbI 2 Br Perovskite Solar Cells.

The charge recombination resulting from bulk defects and interfacial energy level mismatch hinders the improvement of the power conversion efficiency (PCE) and stability of carbon-based inorganic perovskite solar cells (C-IPSCs). Herein, a series of small molecules including ethylenediaminetetraacetic acid (EDTA) and its derivatives (EDTA-Na and EDTA-K) are studied to functionalize the zinc oxide (ZnO) interlayers at the SnO 2 /CsPbI 2 Br buried interface to boost the photovoltaic performance of low-temperature C-IPSCs. This strategy can simultaneously passivate defects in ZnO and perovskite films, adjust interfacial energy level alignment, and release interfacial tensile stress, thereby improving interfacial contact, inhibiting ion migration, alleviating charge recombination, and promoting electron transport. As a result, a maximum PCE of 13.94% with a negligible hysteresis effect is obtained, which is one of the best results reported for low-temperature CsPbI 2 Br C-IPSCs so far. Moreover, the optimized devices without encapsulation demonstrate greatly improved operational stability.