Stability of 2D Perovskite Solar Cells

Solar energy is a renewable energy source more than capable of meeting the world’s energy demand if properly harnessed. New thin film solar cell technologies such as organolead halide perovskite (OHP) solar cells have recently gained prominence for their rapidly increasing power conversion efficiency (PCE) and the possibility of low-cost scalable fabrication methods, such as screen printing and ink-jet printing. Unfortunately, these perovskites are typically unstable when exposed to either humidity or light, thus limiting their usefulness. One method to increase the stability of a common photovoltaic perovskite, methylammonium lead iodide (MAPI), is to create a layered 2D MAPI material by adding a bilayer of n-butylammonium spacer molecules to the crystal structure. The reason that this 2D structure is more stable, however, is not well understood. By using a variety of electrochemical and analytical techniques, we found that the improved stability in such materials is a result of a 2D perovskite specific degradation pathway that produces increasingly stable phases of the 2D perovskite, primarily at the exposed upper layer of the perovskite. These stable phases create a passivating layer and act to slow further degradation reactions. Using this knowledge, we tested a surface treatment designed to form 2D perovskite on the surface of a MAPI solar cell and showed that even a thin layer of 2D perovskite on MAPI can effectively delay device deterioration and preserve conversion efficiency. Furthermore, the choice of alkylammonium spacer can affect the stability of the solar cell when different electrode materials are used, providing a possible route to create stable solar cells using cheaper materials.ChemistryChemical Engineerin