Electrical and photovoltaic characteristics of CuInSe₂ thin films processed by nontoxic Cu-In precursor solutions

Nontoxic Cu-In solution-processed CuInSe₂ absorber thin films and resultant photovoltaic cells have been investigated. Acetate-based Cu-In precursors having different Cu/In ratios of 0.8-1.2 were deposited by spin-coating and then selenized in Se atmosphere up to 550 °C. Single tetragonal CuInSe₂ phase was dominantly obtained regardless of Cu/In ratios, with the segregation of Cu_2-xSe secondary phase only in the case of Cu-rich films as evidenced by Raman spectra. The films with the 1.1 ratio demonstrated a larger grain size of ∼1.06 m with an increased carrier concentration of ∼1.7 × 10¹⁸ cm^-3 and a decreased band gap of ∼1.02 eV, compared to the values obtained for Cu-deficient absorber films. The resultant best cell efficiency was ∼3.1% for the absorber having the 1.1 ratio, suggesting a potential of this simple spin-coating method as an alternative to typical vacuum processes.