HPbI₃ as a Bifunctional Additive for Morphology Control and Grain Boundary Passivation toward Efficient Planar Perovskite Solar Cells

One of the key aspects contributing to the rapid development of perovskite solar cells is to prepare high-quality perovskite films via morphology control and interface engineering. Here, we demonstrate that the additive HPbI3 works effectively on both morphology control and grain boundary passivation of CH3NH3PbI3–xClx thin films. By inducing HPbI3 to the crystal transformation process, high-quality perovskite films consisting of micro-sized grains with boundaries passivated by PbI2 can be readily produced. The perovskite film obtained with HPbI3 as the additive achieves a much longer carrier lifetime compared to the pristine perovskite film without the additive. Under the optimal HPbI3 amount (5.0%), the average power conversion efficiency of the planar-heterojunction solar cells is increased by ∼24% to 17.42% from 14.09% for the device without the additive, and the champion efficiency reaches 18.59%. The devices without any encapsulation show impressive shelf stability, retaining more than 85% of the initial efficiency after being stored in ambient environment for over 40 days.