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.