Structural and Optical Properties of Colloidal Cuinse2 Nanocrystals and its Thermally Evaporated Thin Films for Low-Cost Photovoltaics

We report on the synthesis of colloidal CuInSe2 (CIS) nanocrystals NCs using simple solution-based method. The tetragonal phase CuInSe2 NCs grow in the shape of nanoparticles with an average diameter of 30 nm. The band gap of the grown CuInSe2 NCs is determined to be 1.09 eV. Furthermore, a successful deposition of the grown CuInSe2 NCs in thin film form by vacuum thermal evaporation on Indium-tin-Oxide (ITO) substrates is achieved. The deposition process has been followed by thermal annealing in vacum, for only 5 minutes, at different temperatures (300-346 0 C). We found a strong dependence of the structural, morphologies and optical absorption coefficient of the prepared CIS NCs films on annealing temperature. The formed CIS NCs films have been characterized using UV–Vis-NIR spectroscopy; scanning/transmission electron microscopy (SEM)/(TEM); energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. Optical properties of CIS films were quantified using developed theoretical model based on transmission and reflectance measurements. A remarkable enhancement of the optical absorption coefficient (α~ 3x105 cm-1 ) of the formed CIS NCs films with annealing was demonstrated and suggested the potential use of colloidal CIS for photovoltaic as an active light harvesting material for low-cost solar cells devices.