Molecular Engineering for Two-Dimensional Perovskites with Photovoltaic Efficiency Exceeding 18%

Abstract

<h2>Summary</h2> Two-dimensional (2D) perovskites with excellent stability and optoelectronic properties have aroused great interest for use in perovskite solar cells (PSCs). To date, the power conversion efficiencies (PCEs) of state-of-the art 2D-PSCs are non-satisfactory because of higher recombination losses in 2D quantum wells. Here, based on a series of alkylic ammonium spacers (ethylamine to hexylamine) with different chain lengths, we present a strategy via the molecular van der Waals interaction to realize modified crystallization, phase distribution, and quantum-confined behaviors in Ruddlesden-Popper 2D perovskites (<i>n</i> = 4). With the optimal amylamine (AA) spacer, high-quality 2D perovskites featuring well-aligned phase alignments with fewer unfavorable <i>n</i>-value species and a reduced exciton binding energy have been realized, leading to sufficient charge transfers through different <i>n</i>-value components. The devices based on (AA)₂MA₃Pb₄I₁₃ yield a champion PCE of 18.42%, showing an impressive open-circuit voltage of 1.25 V and a fill factor exceeding 0.80.