Low-bandgap (LBG) mixed tin-lead (Sn−Pb) perovskite solar cells (PSCs) tend to 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.
Now, researchers from China's Soochow University and Sichuan University have reported a mobile ion suppressing strategy that uses 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, the team achieved a champion efficiency of 23.21% for LBG PSCs with an open-circuit voltage (VOC) of 0.900 V, and significantly improved stability.
Integrating these cells with wide-bandgap PSCs into all-perovskite tandem solar cells yielded a high efficiency of 28.55% (certified 28.31%) with negligible hysteresis. The unencapsulated tandem solar cells sustained 90% of its initial PCE following 700 h operation under 1-sun illumination.
This new method provides an effective route to address the adverse hysteresis issues caused by EDADI treatment.
