In-Situ comparative study of photo-induced charge behavior in single-perovskite Cs3Bi2Br9 and double-perovskite Cs2AgBiBr6

• Published in: Optical materials 2024-11, Vol.157, p.116199, Article 116199
• Main Authors: Li, Yangyue, Zhu, Jiaming, Chen, Lu, Bian, Jinxin, Zhu, Weiyan, Meng, Shengyang, Wu, Fan
• Format: Article
• Language: English
• Subjects: Charge behavior; Cs2AgBiBr6; Cs3Bi2Br9; Perovskite; Surface photovoltage
• ISSN: 0925-3467
• DOI: 10.1016/j.optmat.2024.116199

While organic-inorganic lead halide perovskites excel in optoelectronic applications, their use is limited by toxicity and degradation. Consequently, lead-free alternatives like Cs2AgBiBr6, offering greater stability and diverse applications, have been investigated. However, the fundamental structural, optical, and electronic properties of Cs2AgBiBr6 remain insufficiently understood. In this study, we compared the exciton dynamics and photo-induced charge separation in Cs3Bi2Br9 and Cs2AgBiBr6 films using in-situ surface techniques. Both materials display similar surface photovoltage (SPV) peaks in the 450–500 nm range, supporting the hypothesis of Bi 6s-6p orbital transitions in distorted [BiBr6]3− structures. Although many theories propose the presence of self-trapped excitons (STE) in bismuth-based perovskites, sufficient evidence has been lacking. Our observation of a significant redshift in the SPV peak compared to the band edge absorption peak supports STE hypothesis, with Cs2AgBiBr6 showing a more pronounced redshift due to its more complex electronic structure and stronger electron-phonon coupling. Additionally, we observed that Cs2AgBiBr6 exhibits superior charge separation efficiency compared to Cs3Bi2Br9. Notably, Cs2AgBiBr6 shows significantly shorter rise times, indicating more rapid photogenerated charge separation. However, both materials exhibit similar fall times, suggesting comparable charge recombination rates. Light-chopping-frequency dependent SPV measurements further reveal that Cs2AgBiBr6 has a higher charge separation rate than Cs3Bi2Br9. These findings underscore the potential of bismuth-based perovskites for optoelectronic applications and highlight the importance of a comprehensive understanding of their structure-property relationships. •Examined exciton dynamics in Cs3Bi2Br9 and Cs2AgBiBr6 using in-situ surface methods.•SPV confirms the presence of self-trapped excitons in bismuth-based perovskites.•SPV verifies Bi 6s-6p orbital transitions in distorted [BiBr6]3− structures.•LCF-SPV reveals higher charge separation rate in Cs2AgBiBr6 than Cs3Bi2Br9.•Time-dependent SPV shows Cs2AgBiBr6 has shorter rise times compared to Cs3Bi2Br9.