Self-assembly construction of a homojunction of Sn–Pb perovskite using an antioxidant for all-perovskite tandem solar cells with improved efficiency and stability

Abstract

All-perovskite tandem solar cells (PTSCs) demonstrate higher power conversion efficiency (PCE) and lower levelized cost of electricity than single-junction perovskite solar cells (PSCs). However, narrow bandgap (NBG) sub-cells with a Sn–Pb alloy cause severe p-type self-doping by surface oxidized Sn⁴⁺ to generate substantial energy loss and device degradation. Here, we developed a one-step self-assembly strategy to construct a p/p⁻ homojunction of Sn–Pb perovskite using the antioxidant 4-trifluoromethylphenylhydrazine hydrochloride (TFPHCl) and prepared highly efficient and stable NBG PSCs. Self-floating TFPH cations allowed effective defect passivation and inhibition of Sn²⁺–Sn⁴⁺ oxidation, leading to a weak p-type surface (p⁻). Hence, the as-formed p/p⁻ homojunction in turn accelerated the charge separation and reduced the non-radiative recombination. TFPHCl-modified NBG PSCs reached a stabilized PCE of 23.09% with an open-circuit voltage (V_oc) of 0.88 V and excellent operational stability over 780 hours. Coupled with wide bandgap (WBG) subcells, TFPHCl-modified PTSCs ultimately attained an optimal PCE of 27.42% with long-term operational stability over 450 hours.