Thermally\nStable\nAnthracene-Based 2D/3D Heterostructures\nfor Perovskite Solar Cells

Bulky organic cations\nare used in perovskite solar cells\nas a protective\nbarrier against moisture, oxygen, and ion diffusion. However, bulky\ncations can introduce thermal instabilities by reacting with the near-surface\nof the 3D perovskite forming low-dimensional phases, including 2D\nperovskites, and by diffusing away from the surface into the film.\nThis study explores the thermal stability of Cs<sub>0.09</sub>FA<sub>0.91</sub>PbI<sub>3</sub> 3D perovskite surfaces treated with two\nanthracene saltsanthracen-1-ylmethylammonium iodide (AMAI)\nand 2-(anthracen-1-yl)ethylammonium iodide (AEAI)and compares\nthem with the widely used phenethylammonium iodide (PEAI). The steric\nhindrance of AMAI limits the interaction of its NH<sub>3</sub><sup>+</sup> head with the perovskite lattice, relative to what is seen\nwith AEAI and PEAI. As a result, AMAI requires more thermal energy\nto convert the 3D perovskite surface to a 2D perovskite. Annealing\nof perovskite surfaces treated with the iodide salts results in decreased\npower conversion efficiencies (PCEs) for PEAI and AEAI, while a PCE\nenhancement is observed for AMAI. Importantly, AMAI-treated devices\nshow enhanced stability upon annealing of the film and a 100% yield\nof working pixels after a high-temperature stability test at 85 °C,\nrepresenting the most reliable device configuration among all those\nstudied in this work. These results reveal the potential of AMAI as\na scalable surface treatment.