Decoupling light- and oxygen-induced degradation mechanisms of Sn–Pb perovskites in all perovskite tandem solar cells

• Published in: Energy & environmental science
• Main Authors: Bai, Yang, Tian, Ruijia, Sun, Kexuan, Liu, Chang, Lang, Xiting, Yang, Ming, Meng, Yuanyuan, Xiao, Chuanxiao, Wang, Yaohua, Lu, Xiaoyi, Wang, Jingnan, Pan, Haibin, Song, Zhenhua, Zhou, Shujing, Ge, Ziyi
• Format: Journal Article
• Language: English
• Published: 02.08.2024
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/D4EE02427C

Efficiencies of all-perovskite tandem solar cells are dominantly constrained by the challenges pertaining to defects and stability within tin–lead (Sn–Pb) perovskite sub-cells. On top of the well-studied oxygen oxidation, defects related to iodide and the consequent generation of I 2 upon light illumination pose significant degradation risks, leading to Sn 2+ → Sn 4+ oxidation. To address this, we screen phenylhydrazine cation (PEH + )-based additives of varying polarities, which strongly coordinate with Sn for reinforcing the Sn–I bond, and interacting electrostatically with negatively charged defects (V Sn , V FA , I Sn , and I−i). The synergistic effects suppress the photo-induced formation of I 2 and the subsequent oxidation of Sn–Pb perovskites, circumventing the stability concerns of narrow bandgap (NBG) perovskite solar cells (PSCs) under operational conditions. The reducing agent 2-mercaptobenzimidazole (MBI) was further introduced into the precursor solution, which not only demonstrates strong resistance to oxygen erosion, but also reduces the deep-level defect density of the Sn–Pb perovskites. Consequently, single-junction Sn–Pb cells achieve a champion efficiency of 23.0%. The enhanced light stability allows these cells to retain 89.4% of their initial efficiency after 400 hours of continuous operation, as assessed by tracking the maximum power point (MPP). We further integrated the Sn–Pb perovskite into a two-terminal (2T) monolithic all-perovskite tandem cell and achieved a PCE of 27.9% (27.2% certified). Meanwhile, the encapsulated tandem device maintained 90.3% of its initial PCE after 300 h through MPP tracking. The work offers new ideas for tackling the stability issues related to light-triggered oxidation.