Production of single phase chalcopyrite CuInSe2 by spray pyrolysis

Abstract

Thin films (0.5–2 μ) of CuInSe₂ were prepared by spray pyrolysis from solutions with various pH levels and initial Cu:In ratios, and in which the Cu source was either CuCl or CuCl₂. The substrate temperature was varied between 225 and 300 °C. All films prepared with CuCl₂ were chalcopyrite, while only Cu‐rich CuCl based films exhibited this phase. The appearance of Cu_2−xSe and/or Cu₂/Se as a second phase was found to depend strongly on solution stoichiometry, pH, temperature, and substrate. Two layer structures consisting of a Cu‐deficient layer on top of a Cu‐rich layer were produced without the presence of any second phases on both glass and Mo‐coated glass. This is the first time single phase chalcopyrite Cu‐deficient layers have been fabricated by spray pyrolysis. A CuInSe₂/CdS photovoltaic cell made from a single phase double layer filme on glass gave a V_oc of 0.558 V after heat treatment. This V_oc is higher than any reported to date. Absorption spectra have also been measured, and are found to improve when CuCl₂ is used instead of CuCl.