Defect passivation and interface modification by tetra-n-octadecyl ammonium bromide for efficient and stable inverted perovskite solar cells

Charge recombination loss caused by defects and interfaces in the inverted perovskite solar cells (PSCs) significantly impact cell performance and stability. Here, a kind of quaternary ammonium salt of tetra-n-octadecyl ammonium bromide (TODB) with an symmetrical structure is introduced into inverted PSCs to suppress the charge recombination loss. We have comprehensively studied the impact of TODB on the physical properties of the perovskite films and corresponding the performance of the devices. TODB post-treatment results in defect passivation, the built-in electric field enhancement as well as hydrophobicity improvement in the inverted PSCs, which correspondingly enhance device performance and stability. The highest power conversion efficiency (PCE) reaches 20.36 %, which is one of the highest PCE of the inverted PSCs based on methylammonium lead iodide (MAPbI3)/phenyl-C61-butyric acid methyl ester (PCBM) planar heterojunction. The device with TODB modification can maintain 80 % of its initial PCE value in the air for 384 h, while the control device only maintains about 52 % of its initial PCE under the same exposure conditions. This work presents an efficient strategy to improve the performance and stability of the PSCs by passivating the trap states at the interfaces and increasing the hydrophilicity of the perovskite films.