Chemically Anchored PbS‐2PACz CQDs Inks for Scalable HTL in Narrow‐Bandgap and All‐Perovskite Tandem Solar Cells

Abstract Mixed‐metal narrow‐bandgap (NBG) Sn‐Pb perovskites are essential for achieving high‐efficiency all‐perovskite tandem solar cells (APTSCs) . However, their single‐junction performance is limited by interfacial recombination and inefficient charge extraction, due to non‐uniform hole transport layers (HTLs). Here, PbS‐2PACz colloidal quantum dots (CQDs) are synthesized, chemically anchoring [2‐(9H‐carbazol‐9‐yl)ethyl]phosphonic acid (2PACz) onto PbS CQDs via solution‐phase ligand exchange. The resulting PbS‐2PACz CQD ink demonstrates excellent colloidal stability in weakly polar solvents and yields uniform, defect‐suppressing films on perovskites. To further enhance the perovskite/HTL interface, an additional 2PACz treatment deepens the valence band (−5.60 eV), reduces trap density, and optimizes energy‐level alignment. Consequently, NBG perovskite solar cells utilizing PbS‐2PACz with additional 2PACz achieve power conversion efficiencies (PCEs) of 22.84% ± 0.55, exceeding devices using poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and 2PACz self‐assembled monolayers (SAMs). Integrated into APTSCs with a 1.77 eV wide‐bandgap top cell, PbS‐2PACz achieves a PCE of 25.05% ± 0.41, significantly outperforming PEDOT:PSS‐based tandems (21.60% ± 0.91). This work highlights PbS‐2PACz as an effective HTL material that enhances hole extraction, reproducibility, and scalability for high‐performance perovskite solar cells.