Suppressing the Interface Photodegradation towards Efficient and Stable All Perovskite Tandem Solar Cells

All perovskite tandem solar cells (PTSCs) were expected to overcome the Shockley-Queisser limit of single-junction perovskite solar cells (PSCs). Nevertheless, wide bandgap (WBG) subcells suffer from large photovoltage loss and device instability due to extensive film defect, interfacial degradation and phase segregation. Herein, a polymeric multi-dentate anchoring (PMDA) strategy by introducing poly(carbazole phosphonic acid) was employed to engineer the bottom interface and suppress phase segregation. The reinforced and homogeneous anchorage by multiple repeat phosphonic acid groups onto NiO_x significantly optimised the bottom interface, suppressing unfavourable interfacial reactions and thus alleviating phase segregation of WBG perovskite. As a result, the PMDA-modified WBG PSCs showed higher power conversion efficiency (PCE) than the control device (19.84% vs. 18.18%), along with better device photostability (T₈₀ = 1200 vs. 500 h). Coupled with narrow bandgap (NBG) PSCs, the PMDA-modified PTSCs reached a PCE of up to 28.51% with device operation photostability over 700 h (T₈₀).