Improving Performance of Fully Vacuum-Evaporated Perovskite Photovoltaics via Dry Additive Strategy

We demonstrate a “dry additive” strategy to enhance fully vacuum-deposited perovskite solar cells (PSCs) by co-evaporating diphenyl sulfoxide (DPSO) as a volatile solid additive during film formation. Vacuum-processed perovskite films often exhibit high nucleation densities and small grain sizes, which limit crystallinity and increase defects. Introducing DPSO—a Lewis base that temporarily binds perovskite precursors and slows their reaction, modulates nucleation, and enables the growth of much larger perovskite domains. DPSO-treated films show improved crystallinity, lower defect density, and enhanced charge-transport pathways due to reduced grain-boundary density. Power conversion efficiency (PCE) gains are modest for thicker films (peak ∼18.0% vs. ∼17.3% for control at 350 nm), but substantial in ultrathin devices, particularly at 200 nm, where high efficiency is maintained despite significant thickness reduction. PSCs with ∼200 nm active layers achieve PCEs around 17% with DPSO, compared to ∼3% without, and even a 150 nm DPSO-assisted film reaches over 11% efficiency. This capability to fabricate ultrathin (∼150–200 nm) layers with competitive efficiencies is important for developing lightweight and semitransparent solar cells. Notably, the DPSO-based approach also yields enhanced device stability—PSCs retain ∼94% of their initial efficiency after 720 h of ambient storage, far outperforming control devices.