Research and development of CuInTe2 and CdTe based thin film PV solar cells.

The aim of this work was to make low cost thin film solar cells by electrodeposition, using two different materials; copper indium ditelluride (CuInTe[2]) and cadmium telluride (CdTe). CuInTe[2] was chosen to see if it could eliminate the problems associated with the more commonly used materials CuInSe[2] and CuInGaSe[2]. The CdTe was grown by a novel two electrode system and compared with material grown by the conventional three electrode system. Also the chlorine treatment of CdTe was investigated. CuInTe[2] films were electrochemically deposited from aqueous solutions and cyclic voltametry was used to determine suitable deposition parameters. X-ray diffraction, optical absorption and scanning electron microscopy were used to investigate the bulk structure, the band gap energy and the surface morphology of the materials respectively. It was found that layers deposited for 3 hours were ~1.5 mum thick and had a polycrystalline chalcopyrite structure with the band gap varying between 1.05 and 1.30 eV. Current-voltage characteristics of the CuInTe[2]/electrolyte, solid/liquid junctions were measured under dark and illuminated conditions, the layers were found to be photo active and p-type in electrical conduction.CdTe films were electrochemically deposited from aqueous solutions using both two and three electrode systems. Different preparative parameters such as growth voltage and heat treatment conditions were optimised by measuring the I-V characteristic of glass/FTO/CdS/CdTe/Au devices. The device efficiency was high at a growth voltage of 695 mV vs SCE for the 3 electrode system and 1570 mV for the two electrode system. The optimum annealing conditions were 350°C for 20 minutes in air. It is established that treating CdTe with chlorine has a beneficial effect on the solar cell device. For comparison, untreated and treated CdTe were characterised by various techniques. XRD analysis showed a cubic structure, with a significant increase in intensity from the (111) reflection after chlorine treatment. Optical absorption showed a decrease in the band gap energy after chlorine treatment. A considerable change in the morphology between untreated and treated CdTe was observed by SEM. I-V measurements of completed chlorine treated glass/FTO/CdS/CdTe/Au devices showed a significant improvement in efficiency. Furthermore, a comparison was made between the two and three electrode systems; the two electrode system produced a better quality material with higher efficiencies than that obtained by the three electrode system. The best efficiency obtained from the two electrode system was 8.7% while the best efficiency obtained from the three electrode system was 8.4%.