The Recombination Parameter $\gamma$: Modeling and Comments

The recombination parameter
$\gamma$
appears in mathematical expressions for the temperature coefficient of solar cells. This work presents a new analytical expression for this parameter. The expression is derived assuming that all nonradiative recombination occurs in the neutral region of the cell, where carrier diffusion is the dominant transport mechanism. The model shows a direct relation between
$\gamma$
and the temperature sensitivities of the carrier mobility and lifetime. Problems concerning the original definition of
$\gamma$
and its temperature and voltage dependence are discussed and, when possible, amended. A further investigation of the possibility of defect characterization through
$\gamma$
is presented. This yields two analytical expressions that link
$\gamma$
to defect characteristics. A numerical evaluation of the derived expressions is performed for a number of impurities. It is concluded that the recombination parameter
$\gamma$
alone may not be suitable for defect characterization.