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Abstract Surface modification of 3D hybrid perovskites using 2D perovskites, such as phenethylamine halides (PEAX), increases the overall power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). The effect is based on a surface passivation phenomenon where PEAX is in direct contact with the perovskite and hole transport layer (HTL). However, it is herein observed that the PCE of PSCs containing PEAX increases significantly when they are not in direct contact with either the bottom layers (perovskites) or top layers (HTLs). Moreover, the highest PCE (>22%) is obtained for the PSCs when PEAX is not in contact with HTLs by using poly(methyl methacrylate) (PMMA). Photoemission measurements reveal that the shift of the highest occupied molecular orbital of the hole transporting material (a donor‐acceptor‐donor molecule synthesized for the study) to a deeper level results in an increased hole transfer at the perovskite/HTL interface leading to an improved device performance. It is proposed that PEAX acts as dipoles aligned between perovskite and HTL resulting in a shift in the energy levels. The combination of PEAX/PMMA at the interface enables high open‐circuit voltage (1.19V) close to the Shockley–Queisser limit for the triple‐cation (Cs‐MA‐FA) perovskites (bandgap, 1.51 eV).
Kim et al. (Tue,) studied this question.