Luminescence spectroscopy of CdTe/CdS based photovoltaic devices and associated materials

This thesis contains primarily a study of CdTe/CdS heterojunction solar cells, chiefly using photoluminescence spectroscopy. These solar cells show a good potential for commercial power generation in the near future and are of interest to several major companies. A vital but little understood step in the manufacturing process is annealing the cells in the presence of chlorine prior to back contact application. Studies are performed on a selection of thin film CdTe/CdS cells subjected to CdCl_2 anneals of different duration. A chemical bevel etch was used to study the spectra at different depths into the sample and laser intensity and sample temperature variations to identify the mechanisms behind the observed photoluminescence peaks. Evidence was found for the CdCl_2 anneal promoting sulphur diffusion and subsequent grain boundary passivation in the CdTe, leading to increased minority carrier lifetimes and device efficiencies. Attempts to obtain electroluminescence from the CdTe/CdS solar cells were made. By using current pulses electroluminescence was obtained in the 780-850nm range with discernible spectral features. Photoluminescence (PL) studies were also performed on a single crystal of CdTe grown to an unprecedented size of approx. 5 cm diameter at Durham University by a multi-tube seeded vapour method of crystal growth. Much higher resolution spectra were obtained for this than for the solar cells. Several peaks were identified and the mechanisms responsible were theorised. By taking slices of the crystal boule the PL spectra at different points throughout the bulk of the crystal were determined. A series of high quality ion-implanted CdTe crystals were also studied by intensity and temperature dependent PL in order to obtain a better understanding of the effects of known concentrations of known impurities on the PL spectra of CdTe. Specific PL features associated with certain dopants were observed. (author)Available from British Library Document Supply Centre-DSC:DXN042837 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo