2D or Not 2D? Impact of Bulky Cation Deposition Method on Inverted Perovskite Solar Cells

A three-dimensional/two-dimensional (3D/2D) heterojunction interface is well-known for reducing surface recombination in perovskite solar cells. The effectiveness of 3D/2D interfaces has been particularly highlighted in standard (n-i-p) structures. However, their use in inverted (p-i-n) structures is less common due to limitations on the thickness of the 2D phase, which is essential for efficient electron extraction. In this study, we investigate whether 3<i>D</i>/2D dimensional engineering is beneficial in inverted architecture devices by introducing the bulky organic cation 4-chlorophenethylammonium iodide (Cl-PEAI) to triple cation Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.9Br_0.1)₃ perovskite films using two different deposition methods: as a separate interlayer on top of the fully formed 3D perovskite and via an antisolvent approach during film formation. Through low-energy cathodoluminescence measurements─a highly sensitive method for probing the presence of 2D phases on the surface of 3D layers─we reveal that the interlayer method leads to the formation of 2D domains (<i>n</i> = 1 and <i>n</i> = 2). In contrast, the antisolvent method results in surface and grain boundary passivation without the formation of a detectable separate 2D phase. This observation is further correlated with device performance, where passivation leads to improvement, while 2D phase formation does not. These results highlight the significant impact of the deposition method on the formation of the 2D layer over the 3D perovskite in inverted architectures, revealing that 2D phase formation is not always beneficial for device performance in inverted architecture solar cells.