Dispersing SnO ₂ Nanoparticles in Alcohols as an Electron Transport Layer in Organic Solar Cells

Alcohol‐based dispersions of electron transport layers (ETLs) feature low surface tension and rapid drying properties, which are highly desirable for fabricating organic solar cells (OSCs). Tin oxide (SnO 2 ) possesses a wide band gap, high electron mobility, and better UV stability compared with zinc oxide (ZnO). However, when formulated as nanoparticles (NPs), SnO 2 tends to aggregate severely in alcohols, which impairs stable dispersion. In this work, we developed a stable alcohol‐based SnO 2 nanoparticle formulation with tetramethylammonium hydroxide (TMAH) as the dispersant through regulating the polarity of the solvents. High‐polarity solvents (ethanol/water mixture, 2‐methoxyethanol, methanol, ethylene glycol) facilitate the ionization of TMAH and thereby help stabilize SnO 2 NPs via the electro‐steric effect. The stable dispersion exhibited approaching 90% transmittance at its peak in the visible light range (380–750 nm), a dynamic light scattering (DLS)‐measured particle size distribution centered at 10 nm, and long‐term storage stability with no aggregation observed over 1 year. Employing PEIE‐modified SnO 2 as the ETL, the resultant OSCs achieved high power conversion efficiencies (PCEs) of 18.4% (rigid ITO glass substrate) and 17.1% (flexible AgNWs‐em‐ c PVA substrate).