Photovoltaic devices on CdS and Zn(_x) cd(_1-x)S single crystals

Abstract

Photovoltaic devices have gained considerable importance in recent years as a possible alternative solution to the energy problem. The main criterion for these devices for power generation on a large scale is that they must make a positive contribution to the energy balance. With the present level of research and development, CdS and Zn(_x)Cd(_1-x)S based thin film solar cells have emerged as the main contenders in the near future for large scale terrestrial solar energy conversion. However, the many problems with these thin film photovoltaic cells are not yet well understood, although a great deal of effort has been put into their research and development since 1960. In order to avoid the complications associated with polycrystallinity, grain boundaries and other thin film defects, the work reported in this thesis has been carried out on oriented single crystal substrates .The first part of the thesis describes an investigation into CdS/Cu(_2)S devices. This includes the major processes involved in the fabrication of these cells and the determination of the effects variations in these processes have on the electronic and optoelectronic properties of the completed devices. By using the techniques of scanning electron microscopy and reflection electron diffraction in conjunction with conventional electrical and photoelectrical measurement techniques, it has been established that there is a direct correlation between the overall surface topography and resultant device characteristics. Further specific surface features such as ledges and kink sites on etch hillocks are directly associated with the loss of local photovoltaic sensitivity. The chemiplating process by which the surface. layer of CdS is converted into copper sulphide has been improved by introducing three modifications, which enable the chalcocite phase of the copper sulphide to be produced in a much more controlled manner. The effect of a post barrier