The effect of aluminum and boron solid-source doping on recombination in silicon solar cells

The recombination properties of p-type diffusions formed by aluminum diffused into the silicon from an evaporated layer and boron diffused from a B₂O₃ layer deposited on the silicon from solid doping sources is investigated. The contactless photoconductivity decay method was used to separate the emitter saturation current density J_o of the diffusions themselves from the effect of the diffusion process on the bulk lifetime in the substrate. Al diffusions were found to have very high values of J_o, ranging from ~66×10^-13 A/cm² at a diffusion temperature of 850°C, to ~20×10^-13 A/cm² at 1100°C. However, the detrimental effect of these high J_o values on cell efficiency can be managed by reducing the coverage fraction of the diffusions. Bulk lifetimes remained high at ~2000 μs after Al diffusion at temperatures from 850°C to 1100°C