Tuning crystal orientation and charge transport of quasi-2D perovskites via halogen-substituted benzylammonium for efficient solar cells

Quasi-two-dimensional (quasi-2D) perovskites with high stability usually suffers from poor device efficiency. Chemical tuning of the spacer cations has been an effective strategy to achieve efficient and stable quasi-2D perovskite solar cells. Here, we demonstrate that 3-halogon-substituted benzylammonium iodide (3X-BAI, X = F, Cl, Br, I) can significantly affect the orientation of low-dimensional perovskites and charge transport from perovskite to hole extraction layer, as well as device performance. With 3Br-BAI, we achieve the highest device efficiency of 13.21% for quasi-2D perovskites with a nominal n = 3 average composition. Our work provides a facile approach to regulate vertical crystal orientation and charge transport via tuning the molecular structure of organic spacer toward high performance quasi-2D perovskite solar cells.