Selection of appropriate solvent additives for the preparation of high-performance Cs2AgBiBr6 solar cells

Abstract

A high-quality film is essential for the development of high-performance Cs₂AgBiBr₆ solar cells. To enhance the film quality, it is crucial to regulate the crystallization process of Cs₂AgBiBr₆ films. In this study, we introduce Lewis bases including N,N′-dimethylpropyleneurea (DMPU), methylimidazole (MeIm), and ethylenediamine (EDA) as solvent additives into the Cs₂AgBiBr₆ precursor solution. Our findings indicate that the crystallization process and surface morphology of the Cs₂AgBiBr₆ films are significantly influenced by the Gutmann donor numbers (D_N) of the solvent additives. Among the tested additives, MeIm, which has a moderate D_N, effectively regulates the crystallization process. After incorporating MeIm, the Cs₂AgBiBr₆ film demonstrates a more uniform morphology, improved crystallinity, and a reduction in defects. Furthermore, the power conversion efficiency (PCE) of Cs₂AgBiBr₆ solar cells prepared with MeIm reached 2.61%, marking a 38% increase compared to the PCE of 1.89% for those produced without additives. Additionally, a Cs₂AgBiBr₆ solar cell without encapsulation, stored at 15 ± 5 °C and 25 ± 5% humidity for 48 days, retained 97% of the initial efficiency, showcasing remarkable stability. This study offers valuable insights into the solution processing of Cs₂AgBiBr₆ films and supports their application in photovoltaic devices.