Highly Efficient and Air-Stable Heterostructured Perovskite Quantum Dot Solar Cells Using a Solid-State Cation-Exchange Reaction.

Perovskite quantum dots (PQDs) have expanded the scalability of perovskite materials by their high crystallinity, band-gap tunability, and surface ligand-driven functionalities in the colloidal state across optoelectronics as well as photovoltaics. To improve PQD performance in applications, however, defect control has emerged as a major challenge given the increased PQD surface area. Herein, we have developed a heterostructured PQD solar cell by combining CsPbI and FAPbI (FA, formamidinium) PQD layers to introduce a multinary PQD layer based on a solid-state A-site cation-exchange strategy. A heterostructure, including the solid-state diffusion-driven multinary PQD layer, creates an internally graded heterojunction for more efficient charge extraction. The best PQD cell achieves a power conversion efficiency (PCE) of 16.07% with negligible hysteresis. Furthermore, this architecture offers significantly enhanced stability with reduction of trap-assisted recombination as compared to cells of a monocompositional PQD layer. The unencapsulated device retains a 96% PCE after 1000 h in ambient storage.