Structure and temperature dependence of conduction mechanisms in hot wall deposited CuInSe 2 thin films and effect of back contact layer in CuInSe 2 based solar cells

Abstract

Copper indium diselenide (CuInSe 2) was prepared by direct reaction of high purity elemental Copper, Indium and Selenium. CuInSe 2 thin films were prepared on well-cleaned glass substrates by a hot wall deposition technique. The X-ray diffraction studies revealed that all the deposited films are poly crystalline in nature, single phase and exhibit chalcopyrite structure. The crystallites were found to have a preferred orientation along the (112) direction. Structural parameters of CuInSe 2 thin films coated with higher substrate temperatures were also studied. As the substrate temperature increases the grain size increases. The resistivity is found to decrease with increase in temperature. Two types of conduction mechanisms are present in the hot wall deposited CuInSe 2 films. In the temperature region below 215 K the conduction is due to a variable range hopping mechanism and in the temperature region above 215 K the conduction is due to a thermally activated process. It is observed that the solar cell with molybdenum as back contact has low series resistance ( R s), high shunt resistance ( R sh) and large fill factor (FF) when compared with CuInSe 2 based solar cells with other back contact material layers.