Bimolecular Hetero‐Spatial Co‐Passivation Enables Efficient MA‐Free Wide‐Bandgap Perovskites for All‐Perovskite Tandem Solar Cells

ABSTRACT All‐perovskite tandem solar cells (AP‐TSCs) offer the potential to surpass the Shockley–Queisser (S–Q) limit of single‐junction perovskite solar cells (PSCs). Nevertheless, the wide‐bandgap (WBG) sub‐cells suffer from severe open‐circuit voltage ( V OC ) losses induced by surface defects and energy‐level mismatch at the WBG perovskite/C 60 interface. Herein, we implemented a bimolecular passivation strategy by achieving hetero‐spatial distribution of piperazinium bromide (PipBr) and 3‐(methylthio) propylamine hydrobromide (3MTPABr) in the WBG perovskite surface layer. Pip + facilitates a reconstruction of the perovskite surface to form an anchored‐gradient passivation region, while 3MTPA + constructs an ultrathin low‐dimensional perovskite capping layer atop this reconstructed region. This thumbtack‐type spatial distribution of the two molecules effectively passivates surface defects and optimizes the energy‐level alignment at the perovskite/C 60 interface, achieving suppressed interfacial non‐radiative recombination, enhanced charge transport, and improved surface hydrophobicity. Consequently, single‐junction gas‐quenched MA‐free WBG (∼1.76 eV) PSCs achieve a power conversion efficiency (PCE) of 20.80% (with a certified value of 20.02%) and retain 91.1% of their initial PCE after 600 h of operation under 1.0 sun illumination, demonstrating the importance of spatial molecular distribution in WBG perovskite co‐passivation. Notably, the fabricated 2‐terminal AP‐TSC device attains a PCE of 28.34%, highlighting its considerable potential for AP‐TSC applications.