Vertically Oriented Ruddlesden–Popper Phases in Asymmetrical Perovskite Single Crystals for Efficient Solar Cells

The insulating chains of the ammonium cations in two-dimensional (2D) perovskite solar cells (PeSCs) inevitably impede charge transport, thereby limiting the power conversion efficiencies (PCEs). In this study, we develop a vapor venting space-limited crystallization method for growing asymmetric 2D perovskite single crystals (SCs) featuring vertically oriented Ruddlesden–Popper (RP) phases. The high crystallinity and preferred orientation of the 2D layered structures minimize the impact of the bulky side chains of the ammonium cations and facilitated charge transport in the perovskite SCs. The single-crystal PeSCs featuring the aligned RP phases achieve PCEs as high as 14.74%. The PCE is improved to greater than 16% after surface passivation to lower the degree of surface defects. The crystallization method we propose herein minimizes the impact of the long insulting moieties, which are essential for constructing 2D perovskites, and suggests the possibility of obtaining highly efficient 2D single-crystal PeSCs