Study of Optical Properties of CulnSe 2 Thin Film Mohammad Arif Sobhan Bhuiyan and Zahid Hasan Mahmood 1 Department of Applied Physics, Electronics and Communication Engineering, University of Chittagong, Chittagong, Bangladesh 1 Department of Applied Physics, Electronics and Communication Engineering, University of Dhaka 1000, Dhaka, Bangladesh E-mail: zhmjami@yahoo.com ABSTRACT CuInSe 2 is a direct band gap I-Ill-VI ternary solar semiconductor material. The CulnSe 2 thin films for this study were prepared by co-evaporation technique from their elements on glass substrate maintained at temperatures between 2000C and 5000C in a conventional diffusion pump vacuum chamber at pressures of about 10· 5 torr at the Photovoltaic Laboratory of New Castle Upon Tyne Polytechnique, U.K. Shimadzu UV spectrophotometer (model 1201) was used to investigate optical parameters of these films within 350-1100 nm range. Transmittance, reflectance and absorptance of these films were recorded. The absorption co-efficient and the band gap of these films were calculated from these data. INTRODUCTION CulnSe 2 is one of the important solar materials which is still under laboratory research. A study of optical parameters of CuInSe 2 thin films is very important to investigate its suit- ability as the solar material to be used in photovoltaic arrays. CuInSe 2 is a direct band gap I-III-VI ternary semiconductor first synthesized in the year 1953 by Hahn et ale [1]. CuInSe 2 thin films can be produced in different techniques such as thermal evaporation, sputtering or Molecular Beam Epitaxy (MBE). The samples under investigation in the present work were prepared by co-evaporation technique on glass substrates in vacuum chamber under pressure of the order of 10- 5 torr having thickness between 1.9 and 2.2 1m. A crossed Cu-In