Molecularly Induced Carrier‐Polarity Regulation Enables Efficient Methylammonium‐Free Wide‐Bandgap Perovskite Solar Cells

ABSTRACT

Methylammonium (MA)‐free wide‐bandgap (WBG) perovskites are attractive top‐cell absorbers for tandem photovoltaics. However, defect‐related donor‐state contributions can shift the perovskite Fermi level away from the valence‐band maximum (VBM), creating an unfavorable energetic mismatch with the hole‐selective Poly‐4PACZ/perovskite contact and contributing to voltage and fill‐factor losses in perovskite solar cells with an inverted structure. Here, we introduce 4‐(piperidin‐4‐yl)benzoic acid hydrochloride (PBAC) as a spatially organized molecular additive that regulates the carrier polarity of MA‐free WBG perovskites while passivating defects. PBAC shifts the Fermi level toward the VBM and reduces the Fermi‐level offset at the Poly‐4PACZ/perovskite interface. This carrier‐polarity regulation improves energetic compatibility at the hole‐selective contact, facilitating hole extraction and suppressing interfacial recombination. Defect passivation and strain relaxation further inhibit halide migration and stabilize the mixed‐halide lattice. As a result, MA‐free WBG perovskite solar cells with bandgaps of 1.66 and 1.77 eV achieve power conversion efficiencies (PCEs) of 24.66% and 20.74%, respectively. The unencapsulated PBAC‐treated 1.66 eV device retains 86% of its initial PCE after 1000 h of continuous AM 1.5G operation in ambient air. These results establish molecularly induced carrier‐polarity regulation as an effective strategy for reducing interfacial losses in MA‐free WBG perovskite solar cells.