Fast and Selective Photochemical Doping of Spiro-OMeTAD

Oxidizing a redox-active molecule rapidly and selectively to a targeted oxidation state, without residual dopant ions, is a central challenge in molecular doping. Spiro-OMeTAD exemplifies it: the standard LiTFSI/O₂ protocol is slow (>12 h), leaves hygroscopic Li⁺ aggregates in the film, and yields an uncontrolled +1/+2/+3 mixture. Here we report a biphasic photochemical doping platform, the crown ether/acid-assisted doping system (CEADS), in which a chlorobenzene solution of spiro-OMeTAD/LiTFSI is layered above an aqueous phase of concentrated HCl and 12-crown-4 (12C4) and irradiated with broadband UV. Doping completes in 60 s, yielding a > 10⁴-fold conductivity enhancement (σ = 1.18 × 10^-2 S cm^-1, ≈60-fold over LiTFSI/O₂) and removing >98% of Li⁺ from the organic phase. Three sequentially optimized parameters control the spiro-OMeTAD oxidation manifold: high H⁺ quenches over-oxidation, Cl^- provides secondary kinetic modulation at intermediate acid, and 4 equiv 12C4 enforces charge-balanced phase transfer. Temperature-dependent conductivity yields an Arrhenius activation energy E_a = 0.19 eV (R² = 0.99) over 193-298 K, consistent with reduced Li-related deep traps. CEADS produces lithium-free, cleanly +1/+2-oxidized hole-transport films on a minute timescale.