Molecular interfaces drive vertical crystallization in Dion-Jacobson perovskite solar cells

Two-dimensional perovskites are promising candidates for photovoltaics due to their intrinsic structural stability, but their efficiency is often limited by poor charge transport, in part due to unfavorable crystal orientation. Here, we report a molecular interface engineering strategy using dual-anchoring organic acids, croconic acid (CA) and squaric acid (SA), to direct vertical crystallization in Dion-Jacobson (DJ) perovskite films. These molecules form robust inter-layers between the NiO_x hole transport layer and TTDMA (thieno[3,2-b]thiophene-2,5-diyldimethanaminium)–based DJ perovskites (nominal n = 4), with SA exhibiting ordered vertical orientation via bidentate coordination. This templated interface promotes vertical orientation, reduces interfacial defects and lattice strain, and suppresses Ni³⁺induced oxidation of I⁻. As a result, devices incorporating SA achieve a champion power conversion efficiency of 22.03% (certified 21.42%) along with outstanding operational stability. This study demonstrates a general molecular interface strategy to direct vertical crystallization and improve the performance of layered perovskite solar cells.