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Solar cells are, in their simplest form, large area p-n junctions. Light falls upon the upper
surface, is absorbed, and generates electron-hole pairs which are separated by the electric field
associated with the depletion region. The performance of a solar cell is generally believed to be closely
related to the precise nature of the surfaces and interfaces involved. The nature of the surfaces and
interfaces is in turn related to the exact conditions under which the cell was fabricated.
Traditionally the optimum production conditions have been determined directly and empirically,
and the influence of the precise nature of the cell on its performance has not been a matter of major
concern. This approach has met with considerable success for several types of cell. However some
applications make stringent demands on solar cells. An example of this would be the long operating
lifetimes required of solar cells used in space environments where radiation tends to cause degradation.
For this type of application more exotic semiconductors are of interest. The high cost of these
materials means that empirical methods for optimising fabrication conditions are not viable and models
have been developed to predict the optimum cell structure. Most models operate by solution of the
transport equations(1 ). The model described here is based on the Transmission Line Matrix (TLM)
method which is a technique of transient analysis. An iterative technique has been chosen since it gives
the greatest flexibility to incorporate spacial variations in parameters. Of iterative techniques available,
TLM has many advantages in terms of implementation as well as being rather more accessible to
non-mathematicians
In this case the particular cell of interest is the ITO-InP based solar cell. In this structure the
rf- sputtered ITO film acts as a transparent conductor and a shallow p-n junction exists within the
single crystal InP(2,3).
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