Thin film solar cells with a band gap graded in the thickness direction were prepared by vacuum evaporation of various alloys of Cadmium Sulphide (CdS) and Cadmium Telluride (CdTe) onto glass substrates. Theoretical computer analyses were carried out and show that a solar cell with a graded band gap surface layer ought to be a more efficient photovoltaic converter than a conventional homojunction device. A vacuum evaporator capable of multiple simultaneous co-evaporations was built and used initially to deposit only the CdS and CdTe films and subsequently mixed and graded films of Cadmium Sulphide Telluride (CdS x Te 1-x). The composition of the mixed and graded films was controlled by a set of shutters built above the sources, rather than by the control of the temperature of the sources. The electronic properties of the films were adjusted by co-evaporation of dopant materials such as Cadmium (Cd), Indium (In) and Copper (Cu), and measured by Hall Effect measurements. The physical properties of the films such as the band gap, crystal phase and grain size were investigated by optical transmission measurements, X-ray analysis and scanning electron microscopy respectively. Finally, p-n junctions with n-type graded band gap surface layers on top of either pure p-type CdTe films or mixed p-type CdS0.5Te0.5 films were prepared. However, the photoresponse of these structures was low, probably due to very short minority carrier life-times, lack of low resistance contacts and cross diffusion of dopant materials. Nevertheless, the characteristics of individual materials and the spectral response of the devices indicated that if these problems could be solved, a successful solar cell could be made.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:483422 |
| Date | January 1978 |
| Creators | Radojcic, R. |
| Publisher | University of Salford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://usir.salford.ac.uk/2174/ |
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