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 eta(d) and two types of trapping efficacy eta(t) and eta(SRH) are proposed. The relationship of eta(d), eta(t), and eta(SRH) is formulated. Various values of eta(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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4719046]