Synergistic Passivation Effects of Li‐Al Co‐Doping Enables >15% Efficient Kesterite Photovoltaics

Cation doping has been widely explored to mitigate disorder in kesterite Cu 2 ZnSn(S, Se) 4 photovoltaics, yet further efficiency gains are hindered by the inability to simultaneously suppress deep‐level defect clusters, enhance carrier concentration, and preserve bulk transport properties. Here, we report a Li‐Al co‐doping strategy that introduces synergistic passivation effects (SPEs) within the absorber. Unlike simple additive doping, the co‐substitution of Li + and Al 3+ at Zn 2+ sites with Li preferentially occupying Zn sites in the presence of Al, as confirmed by first‐principles density functional theory (DFT) open‐circuit voltage calculations, enables a unique charge self‐compensation and lattice strain balance mechanism, which collectively reshapes the defect landscape. This approach effectively suppresses detrimental [2Cu Zn +Sn Zn ] clusters while promoting beneficial [V Cu +Zn Cu ] clusters, and concurrently increases carrier concentration and built‐in potential. Comprehensive spectroscopic and electrical characterizations reveal that the SPEs originate from energetically favorable defect complexes such as [Li Zn +Al Zn ], enabling atomic‐scale tuning of recombination dynamics. As a result, the champion device achieves a notable efficiency of 15.49% with a high open‐circuit voltage ( V OC ) of 0.608 V ( V OC,def = 0.286 V), and exceptional operational stability over 3910 h. This work establishes a generalizable materials design principle, i.e., engineering synergistic charge compensation between complementary dopants for overcoming voltage deficits in multi‐cation semiconductors beyond kesterites.