Interface Engineering of Imidazolium Ionic Liquids toward Efficient and Stable CsPbBr₃ Perovskite Solar Cells

TLDR

Defect passivation of perovskite films is an effective strategy to boost power conversion efficiency and long‑term stability of perovskite solar cells. This study investigates the use of 1‑butyl‑2,3‑dimethylimidazolium chloride ionic liquids as a modification layer to passivate surface defects in carbon‑based CsPbBr₃ perovskite solar cells without a hole‑transporting material. The ionic liquid is applied as a surface modification layer on the perovskite film, aligning the valence band with the carbon electrode work function and reducing non‑radiative and radiative recombination. The [BMMIm]Cl modifier improves the device to a champion efficiency of 9.92 % (Voc 1.61 V), a 61.3 % increase over the control, and yields excellent long‑term stability under high humidity, high temperature, and continuous illumination, demonstrating that IL passivation effectively enhances both efficiency and durability of CsPbBr₃ PSCs.

Abstract

The defect passivation of perovskite films is an efficacious way to further boost the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). In this work, ionic liquids (ILs) of 1-butyl-2,3-dimethylimidazolium chloride ([BMMIm]Cl) are used as a modification layer in perovskite films in carbon-based CsPbBr3 PSCs without a hole-transporting material (HTM) for passivating the surface defects. The preliminary results demonstrate that the [BMMIm]Cl modifier passivates the surface defects of the perovskite film and reduces the valence band of perovskite close to the work function of the carbon electrode, which causes a remarkably inhibited nonradiative and radiative charge recombination, improved energy-level matching, and decreased energy loss. After optimization, a champion efficiency of 9.92% with a Voc as high as 1.61 V is achieved for the [BMMIm]Cl tailored carbon-based CsPbBr3 PSC without HTM, which is improved by 61.3% in comparison with 6.15% for the control device. Furthermore, the encapsulation-free PSC presents good long-term stability after storage in an air atmosphere with 70% RH at 20 °C or 0% RH at 80 °C as well as under continuous illumination conditions for 30 days. The significantly improved PCE and stability in high humidity or temperature suggest that the perovskite passivation by ILs is an effective strategy for fabricating high-PCE and stable PSCs.