Interface modification by a multifunctional ammonium salt for high performance and stable planar perovskite solar cells

Abstract

Perovskite solar cells (PSCs) have realized a power conversion efficiency (PCE) of 23.7%. However, defects and a high moisture sensitivity limit the further development of perovskite device performance. This study shows that cetyl trimethyl ammonium bromide (CTAB), a multifunctional ammonium salt, plays dual roles in passivating the perovskite defects and improving the moisture stability. Attaching a long carbon chain to the perovskite surface improves the humidity stability. The ammonium group in the CTA⁺ cation can anchor to the surface of the MAPbI₃ film to passivate defects without the formation of a secondary phase, and Br⁻ is uniformly distributed on the surface and has a gradient distribution in the vertical direction. Furthermore, by optimizing the CTAB solution concentration, the MAPbI₃ device with CTAB demonstrated an optimum power conversion efficiency (PCE) of 18.95% with a steady-state output PCE of 18.11%. Finally, the MAPbI₃ device treated with CTAB exhibited better moisture resistance, with no obvious decline observed during the storage stability test for 1600 h under dry conditions in the dark. Furthermore, the device treated with CTAB showed better operational stability under 1 sun illumination at the maximum power point (retaining over 60% of its initial PCE for 1800 min) compared with that of the MAPbI₃ device.