In Situ Surface Reconstruction Towards Planar Heterojunction for Efficient and Stable FAPbI 3 Quantum Dot Solar Cells.

Pure-phase α-FAPbI 3 quantum dots (QDs) have been the focus of an increasing interest in photovoltaics due to their superior ambient stability, large absorption coefficient and long charge-carrier lifetime. However, the trap states induced by the ligand-exchange process limit the photovoltaic performances. Here, we develop a simple post treatment using methylamine thiocyanate (MASCN) to reconstruct the FAPbI 3 -QD film surface, in which a MAPbI 3 capping layer with a thickness of 6.2 nm is formed on the film top. This planar perovskite heterojunction leads to a reduced density of trap-states, a decreased band gap, and a facilitated charge carrier transport. As a result, a record high power conversion efficiency (PCE) of 16.23% with negligible hysteresis is achieved for the FAPbI 3 QD solar cell, and it retains over 90% of the initial PCE after being stored in ambient environment for 1000 h. This article is protected by copyright. All rights reserved.