Synergistic immobilization of ions in mixed tin-lead and all-perovskite tandem solar cells
Yuhui Liu, Tianshu Ma, Changlei Wang, Zhenhai Yang, Yue Zhao, Zhanghao Wu, Chen Chen, Yining Bao, Yuhang Zhai, Tianci Jia, Cong Chen, Dewei Zhao, Xiaofeng Li
Abstract
Low-bandgap (LBG) mixed tin-lead (Sn−Pb) perovskite solar cells (PSCs) suffer from inferior performance due to their high defect density. Conventionally, ethylenediammonium diiodide (EDADI) is used as a surface passivator to reduce defects and improve device photovoltaic performance, but it introduces severe hysteresis caused by excessive mobilized ions at the top interface. Here, we report a mobile ion suppressing strategy of using hydrazine monohydrochloride (HM) as a bulk passivator to anchor the free ions in LBG perovskites. The protonated hydrazine (N2H5+) of HM formed hydrogen bonds with iodine (I–) ions, while the chloride (Cl–) ions occupied the I– vacancies, collectively impeding the migration of I– and thus mitigating the ion movement-induced hysteresis that arose from EDADI usage. The synergistic strategy of HM doping and EDADI post-treatment significantly suppresses the oxidation of Sn2+, decreases trap density, and inhibits rapid crystallization of perovskite. Consequently, we achieved a champion efficiency of 23.21% for LBG PSCs. Integrating these cells with wide-bandgap PSCs into all-perovskite tandem solar cells yields a high efficiency of 28.55% (certified 28.31%) with negligible hysteresis. The introduction of ethylenediammonium diiodide reduces defects but also leads to severe hysteresis caused by excessive mobilized ions. Here, authors employ hydrazine monohydrochloride as a bulk passivator to mitigate such hysteresis, achieving maximum efficiency of 28.55% for tandem solar cells.