Vertical distribution of PbI2 nanosheets for robust air-processed perovskite solar cells

The fabrication of perovskite solar cells (PSCs) in ambient air is technologically favorable for commercialization, however, the photovoltaic performance of ambient-processed PSCs is still lagging behind their inert counterparts. One major challenge is the growth of high-quality perovskite films regardless of the ambient humidity. Here, we demonstrate an effective strategy to grow robust perovskite film with enlarged grain size, enhanced crystallinity, and preferred orientation in high-humidity air. More particularly, PbI2 2D nanosheets are formed and vertically distributed at the grain boundaries of perovskite films, playing a powerful passivation role. Upon our regulation of the crystallization of perovskite film and the distribution of PbI2, the according device shows significant improvement in efficiency and stability. As a result, we achieve a maximum power conversion efficiency (PCE) of 19.83% for MAPbI3-based device and over 21% for MA0.6FA0.4PbI3-based device. Moreover, these devices display remarkably improved operational stability in ambient air without encapsulation. This work provides a reliable and cost-effective strategy for the commercial manufacturing of PSCs.