Influences of donor defect passivation on the performance of Cu(In,Ga)Se₂ thin-film solar cell

Abstract

In this work, the study of donor defect passivation in CIGS solar cell was simulated by wxAMPS software. The effects of near-interface shallow donor defect and bulk donor defect on the performances of solar cell were investigated mainly through changing the state densities and their position distributions. The results show that the high density of the near-interface shallow donor defect state decreases the open circuit voltage. By contrast, the low density of the near-interface shallow donor defect state has the higher open circuit voltage and short-circuit current density. But it easily leads to the CdS conduction band offset increased, then raising carrier recombination rate which decreases the fill factor. For the passivation of the bulk donor defect in the absorption layer, the performances of the CIGS solar cell are much dependent on the position distribution of donor defect state density. Among them, the decrease of the state density in the space charge region can improve the open-circuit voltage. Meanwhile, the reduction of the state density in the quasi-neutral region can increase the short-circuit current density. With the bulk donor defect state density decreased, the conversion efficiency will saturate due to the limitation of the acceptor concentration. When the donor defect state density is low enough, the influence of capture cross section on the device performance is reduced. The conversion efficiencies varying with passivation region were compared from two directions (CdS to Mo and Mo to CdS). It was found the passivation of the donor defect in the transition region where the position from the quasi-neutral region to the space charge region in the absorption was critical to the improvement in the conversion efficiency of the solar cell under a suitable alkali element concentration.