Anion regulation engineering for efficient Ruddlesden-Popper inverted perovskite solar cells

Recently, many studies have focused on exploiting new spacer cations to boost the power conversion efficiency (PCE) of Quasi-two-dimensional (Q-2D) Ruddlesden-Popper (RP) perovskites solar cells (PSCs). As another essential part of RP perovskite structure, halogen anions have a substantial impact on crystalline quality. However, there are few studies about how halogen anions affect RP PSCs and their possible underlying mechanisms. Here, we investigate different halide anions that impact the optoelectronic properties of RP perovskite films. Specifically, we use PEAI, PEABr, and PEACl (PEA = phenethylammonium) to fabricate RP perovskite films based on PEA2MA3Pb4I11X2 (X = I, Br or Cl, n = 4) for systematical study. Through a series of characterizations and analyses, RP perovskite films with PEACl show a higher proportion of vertical crystal orientation and fewer trap-states, which leads to improved carrier transmission pathways. As a result, the devices based on PEACl (PEA2MA3Pb4I11Cl2, n = 4) achieve a champion PCE of 12.02%, which is higher than PEAI (6.76%, PEA2MA3Pb4I13, n = 4) and PEABr (4.26%, PEA2MA3Pb4I11Br2, n = 4).