Recombination-enhanced Processes in Solar Cell Degradation*

For the purposes of this paper we shall consider any process enhanced by raising carrier densities as recombinat ion enhanced, even where the carrier densities are raised by ionizing radiation, injection or some indirect mechanism. These processes have two special features. (1) Either the processes are athermal or they show only a weak temperature dependence. As a result, processes may occur at low temperatures which cannot be predicted by simple extrapolation from high temperatures. (2) The processes occur during device operation and hardly ever "on the shelf". The rate depends on the excitation rate as well as on the total dose. In a solar cell system, any part may be affected. The ancillary parts such as protective windows and antireflection coatings are also liable to damage. Recombinat ion enhancement is obviously particularly important when high optical densities occur (as with solar concentrators) or other special operating conditions. This paper is an extension of an earlier discussion [1] and in it we consider some general aspects of enhanced processes. The consequences of enhanced processes can be varied: point defect production, dislocation climb,