Crystallinity-guided dual modification of wide bandgap perovskite for efficient four-terminal perovskite/silicon tandem solar cells

Abstract

Wide-bandgap (WBG) perovskite solar cells (PSCs) are essential top absorbers in perovskite/silicon tandem solar cells. However, their power conversion efficiencies (PCEs) are limited by poor crystallization, abundant trap states, and defect-mediated nonradiative recombination in both the bulk and at the surface. Here, we introduce a dual-modification treatment that couples phenylurea (Ph-urea) as a bulk additive with fluorinated phenethylammonium iodide (F-PEAI) as a surface passivant to synergistically enhance crystallinity, passivate defects, and suppress nonradiative losses. Ph-urea enhances bulk crystallinity and structural coherence through Pb⋯O=C coordination, leading to uniform nucleation and enlarged grains, while F-PEAI forms a thin two-dimensional (2D) capping layer atop the ordered three-dimensional (3D) lattice, creating a surface-confined 2D/3D heterostructure. Structural and spectroscopic analyses confirm enhanced crystallinity, the emergence of low-angle 2D diffraction features, and a stabilized surface-localized PbI2 phase, indicating effective bulk-surface defect regulation. This cooperative modification lowers the trap density by nearly threefold, substantially prolongs carrier lifetimes, and markedly suppresses trap-mediated recombination. As a result, Cs0.22FA0.78Pb(I0.85Br0.15)3 WBG-PSCs deliver a champion PCE of 22.68%, compared with 19.67% for pristine devices. Semitransparent devices retain ∼20% PCE with strong near-infrared transparency, enabling efficient spectral splitting in four-terminal perovskite/silicon tandems that reach 30.90% efficiency. These findings demonstrate that synergistic crystallinity enhancement and selective 2D surface reconstruction provide a robust pathway for producing defect-suppressed, tandem-compatible WBG absorbers.