Dual roles of doping and trapping of semiconductor defect levels and their ramification to thin film photovoltaics

It is pointed out that the semiconductor localized intrinsic/impurity defect levels' dual roles for carrier doping and trapping (Shockley-Read-Hall generation-recombination) have been treated differently and inconsistently. It is proposed that instead of ionization or activation energy, transition Gibbs free energy level should be used for the dual roles of doping-trapping. To qualitatively evaluate the effectiveness of doping and of trapping, the concept of doping efficacy η _d and two types of trapping efficacy η t and η _SRH are proposed. The relationship of η _d, η _t, and η _SRH is formulated. Various values of η _SRH for different types of defect levels are presented. General ramification of the proposed concepts and efficacy of trapping is explored for polycrystalline thin film solar cells.