Power, Recombination and the Ideality Factor

It was shown in 1957 that while normally a = 1, the recombination in the space charge region can lead to a = 2. We shall therefore, without further enquiry, study (3.4) in the generalised form (3.4a) 

The maximum power output occurs at a voltage such that 

This is the so-called fill factor which is a product of two factors, each smaller than unity. This expression is in the literature only for the case Jq - 0, when it is  

As a is increased there is often a tendency for the maximum power output to decrease, particularly when recombination in the transition region mops up photo-excited carriers which are then not available for the generation of electricity. On the other 

It has also been confirmed by direct experiment that life times tend to be greater, and recombination traffic to be smaller, for cells having lower a-values. Low a-values are therefore preferable( ). 

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