The preparation of thin film graded band gap solar cells

Radojcic, R

Abstract

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.

Citation

Radojcic, R. The preparation of thin film graded band gap solar cells. (Thesis). University of Salford, UK

• Thesis Type: Thesis
• Deposit Date: Jul 1, 2009
• Publicly Available Date: Jul 1, 2009
• Award Date: Aug 1, 1978