Transparent p-type CuBr 1%x I x semiconducting thin films with a variable band gap were prepared using spin coating, which is a non-vacuum process. The dependence of their structural and optical properties on the CuBr 1%x I x composition was investigated. In X-ray diffraction patterns, the dominant CuBr 1%x I x peak was found to shift to higher angles with decreasing mixing ratio x. The Z 1,2 and Z 3 exciton absorption bands were observed from 300 to 400 nm, and the absorption wavelength varied with x. The ionization potential was determined using photo yield spectroscopy, and was found to increase with increasing x. These results suggest that the valence band maximum for CuBr 1%x I x depends on the composition. The results obtained in the present study allowed the energy band structure for this material to be proposed.