Facile CuI Thin Film Fabrication

All reagents were purchased from Sigma–Aldrich or Alfa Aesar and were used without further purification. A 0.144 m pristine CuI solution was prepared by dissolving CuI (99.999%, Sigma–Aldrich) in acetonitrile (anhydrous, 99.8%, Sigma–Aldrich). Each dopant solution was prepared by dissolving the dopants in dimethylsulfoxide (anhydrous, 99.9% Sigma–Aldrich) at a concentration of 0.05 m. Thiourea (99.99%, Alfa Aesar), N‐methylThiourea (97%, Sigma–Aldrich), N‐ethylThiourea (99%, Sigma–Aldrich), N‐propylThiourea (98%, Alfa Aesar), N‐isopropylThiourea (98%, Alfa Aesar), N‐butylThiourea (Sigma–Aldrich), N‐tertiarybutylThiourea (Sigma–Aldrich), N,N’‐dimethylThiourea (99%, Sigma–Aldrich), potassium ethylxanthogenate (96%, Sigma–Aldrich), and 1,2‐ethanedithiol (≥98.0%, Sigma–Aldrich) were used as dopants in this experiment. The solution of CuI and dopants were combined in the desired molar ratios (0.5–10%) and stirred for 30 min prior to use.