Universal approach toward high-efficiency two-dimensional perovskite solar cells a vertical-rotation process

The emerging 2D perovskites exhibit superior stability and similar optoelectronic attributes compared to the 3D analogues, but their strong exciton-binding energy and inferior interlayer charge-transport reduce dramatically the device performance. Herein, we report a universal approach towards high-efficiency 2D perovskite solar cells (PSCs) by using the synergistic effect of NH 4 Cl and H 2 O to rotate the crystallographic orientation of 2D systems. The preferential adsorption of NH 4 Cl to the (202) crystal plane and the accelerated deprotonation of NH 4 + by H 2 O guide the crystal growth of the 2D framework towards vertical out-of-plane orientation, which strongly improves the 2D crystallinity, charge mobility, and carrier lifetime. As a representative, (PEA) 2 (MA) 3 Pb 4 I 13 -based PSCs ( n ≤ 4) prepared via the vertical-rotation process achieve a champion power conversion efficiency (PCE) of 17.03%, among the best PCEs reported for 2D PSCs. These findings offer a universal approach to rotate the orientation of 2D perovskites for efficient photovoltaics regardless of the perovskite composition. A universal vertically-rotated (VR) methodology is proposed to rotate the crystal orientation of 2D perovskites, which improves charge transport properties by several orders of magnitude and boosts the efficiency of 2D ( n ≤ 4) PSCs to above 17%.