Thermally Stable Anthracene-Based 2D/3D Heterostructures for Perovskite Solar Cells.

Bulky organic cations are used in perovskite solar cells as a protective barrier against moisture, oxygen, and ion diffusion. However, bulky cations can introduce thermal instabilities by reacting with the near-surface of the 3D perovskite forming low-dimensional phases, including 2D perovskites, and by diffusing away from the surface into the film. This study explores the thermal stability of CsFAPbI 3D perovskite surfaces treated with two anthracene salts─anthracen-1-ylmethylammonium iodide (AMAI) and 2-(anthracen-1-yl)ethylammonium iodide (AEAI)─and compares them with the widely used phenethylammonium iodide (PEAI). The steric hindrance of AMAI limits the interaction of its NH head with the perovskite lattice, relative to what is seen with AEAI and PEAI. As a result, AMAI requires more thermal energy to convert the 3D perovskite surface to a 2D perovskite. Annealing of perovskite surfaces treated with the iodide salts results in decreased power conversion efficiencies (PCEs) for PEAI and AEAI, while a PCE enhancement is observed for AMAI. Importantly, AMAI-treated devices show enhanced stability upon annealing of the film and a 100% yield of working pixels after a high-temperature stability test at 85 °C, representing the most reliable device configuration among all those studied in this work. These results reveal the potential of AMAI as a scalable surface treatment.