Homogenizing Vertical Strain Distribution Enables High‐Performance Tin‐Based Perovskite Solar Cells With Thicker Absorber via Two‐Step Deposition

ABSTRACT

Owing to typically restricted active layer thickness (∼200 nm), solution‐processed tin‐based perovskite solar cells (TPVSCs) suffer from incomplete photon‐to‐electron conversion, which fundamentally limits power conversion efficiency (PCE). Unfortunately, we uncover for the first time that increasing the active layer thickness induces detrimental vertical lattice strain gradient and faster crystallization rate, which exacerbate defect formation and ultimately cause a severe mismatch between electron diffusion length and absorber thickness in the tin‐based perovskite device. To address this, we innovatively introduce reductive 4,4′‐thiobisbenzenethiol (TBBT), whose ‐SH groups can form bidentate coordination with Sn ²⁺ ions. This interaction can relax Sn‐I bonds, which is beneficial for lattice homogeneity. Concurrently, it retards crystallization kinetics, thus achieving an electron diffusion length commensurate with active layer thickness. Ultimately, the excellent PCEs of 15.02% (certified 14.78%) for rigid devices and 12.43% for flexible devices at 0.04 cm ² , and 13.37% for rigid devices at 1.00 cm ² are achieved. Notably, the unencapsulated rigid device retains T ₉₅ of 3500 h shelf storage and T ₉₀ of 684 h under MPP tracking. Meanwhile, the flexible device maintains 85% of its initial PCE after 4000 bending cycles. These results demonstrate that our strategy yields synergistic gains in both efficiency and stability.