Parametric simulation of the back-surface field effect in the silicon solar cell

Abstract

Recombination of minority carriers in the solar cell is a major contributing factor in the loss of quantum efficiency and cell power. While the surface recombination is dealt with by depositing a passivation layer of SiO2 or SiNx, the bulk recombination is minimized by use of nearly defect-free monocrystalline substrate. In addition, the back-surface field (BSF) effect has been very useful in aiding the separation of free electrons and holes in the bulk. In this study, the key BSF parameters and their effect on the performance of a typical p-type front-lit Si solar cell are investigated by use of Medici, a 2-dimensional device simulator. Of the parameters, the doping concentration of the BSF layer is found to be most significant. That is, for a p-type substrate of 1 × 1014 cm−3 acceptor concentration, the optimum doping concentration of the BSF layer is 1 × 1018 cm−3 or more, and the maximum cell power can be increased by 24%, i.e., 25.4 mW cm−2 vs. 20.5 mW cm−2, by using a BSF layer with optimum doping. With regards to the BSF layer thickness, the impact is less. That is, the maximum cell power is about 11% higher at 100 μm than at 5 μm, which translates to an increase of 1.2% μm−1. In practice, therefore, it would be better to rely on the control of the doping concentration than the thickness in maximizing the BSF effect in real Si solar cells.