EFFECT OF TRAP LOCATION AND TRAP-ASSISTED AUGER RECOMBINATION ON SILICON SOLAR-CELL PERFORMANCE

Model calculations were performed to investigate and quantify the effe ct of trap location and trap-assisted Anger recombination on silicon s olar cell performance. Trap location has a significant influence on th e lifetime behavior as a function of doping and injected carrier conce ntration in silicon. It is shown in this paper that for a high quality silicon (tau = 10 ms at 200 ohm-cm, no intentional doping), high resi stivity (greater than or equal to 200 ohm-cm) is optimum for high effi ciency one sun solar cells if the lifetime limiting trap is located ne ar midgap. However, if the trap is shallow (E(t) - E(v) less than or e qual to 0.2 eV), the optimum resistivity shifts to about 0.2 ohm-cm. F or a low quality silicon material or technology (10 mu s at 200 ohm-cm , prior to intentional doping) the optimum base resistivity for one su n solar cells is found to be similar to 0.2 ohm-cm, regardless of the trap location. It is shown that the presence of a shallow trap can sig nificantly degrade the performance of a concentrator cell fabricated o n high-resistivity high-lifetime silicon material because of an undesi rable injection level dependence in the carrier lifetime. The effect o f trap assisted Auger recombination on the cell performance has also b een modelled in this paper. It is found that the trap-assisted Auger r ecombination does not influence the one sun cell performance appreciab ly, but can degrade the concentrator cell performance if the trap-assi sted Auger recombination coefficient value exceeds 2 x 10(-14) cm(3)/s . Therefore, it is necessary to,know the starting lifetime as well as trap location in order to specify base resistivity in order to predict or achieve the best cell performance for a given one sun or concentra tor cell design.