Preparation and Properties of Thin Films of Copper Indium Diselenide Produced by Flash Evaporation and Electrodeposition Techniques.

CuInSe_2 is a member of the I-III-VI_2 group of semiconductors and exists in the chalcopyrite phase belonging to the zinc blende family. Its optical and electrical properties and durability make it a valuable photovoltaic material. Economical analysis of solar cells indicates the necessity of producing polycrystalline thin films to reduce costs, and CuInSe _2 is suited to this. Of the various techniques available, flash evaporation and cathodic electrodeposition of the three elements were chosen as they are in principle simple, speedy and inexpensive. These techniques have often been associated with problems such as irreproducibility, nonstoichiometry and structural nonuniformities, however, these were overcome. The properties of flash evaporated CuInSe_2 films were found to be strongly dependent on the substrate and source temperatures. Elemental electrodeposition was achieved from aqueous solutions containing CuCl, InCl_3 and SeO_2 and depended on the solution pH and concentration and the applied current. Structural characterizations were carried out by energy dispersive spectroscopy analysis, X-ray diffraction and scanning and transmission electron microscopy studies. These confirmed the presence of chalcopyrite phase, near stoichiometric, uniform CuInSe_2 . Optical absorption studies indicated direct bandgaps of 1.02 and 1.1eV for flash evaporated and electrodeposited films respectively. Electrical measurements were obtained from Hall affect and resistivity studies. Untreated flash evaporated and electrodeposited films were p-type with room temperature resistivity and mobility values of 2.14 times 10^{-3 }Omegacm, 8.1 cm^2/Vs and 3 times 10^{ -2}Omegacm, 4 cm^2/Vs respectively. After indium diffusion to produce n-type conductivity, these became 1.11 times 10^{-4}Omegacm, 23.76cm^2/Vs and 22 times 10^{-2}Omegacm, 2 cm^2/Vs respectively. Photovoltaic (PV) and photoelectrochemical (PEC) solar cells were fabricated with respective configuration of Mo/p-CuInSe_2 /n-CdS/Au and Mo/n-CuInSe_2/I ^-I_3^-/C. Under 85mW/cm^{-2} illumination intensity the open circuit photovoltages and short circuit current densities were 188mV, 0.056mAcm^ {-2} (PV), 172mV, 2.75 mAcm^ {-2} (PEC) and 200mV, 10mAcm^ {-2} (PEC) for electrodeposited and flash evaporated films respectively. Generally, the films were of good quality and the photoactivity displayed by them show promise for development in their application to solar cell devices.