Role of lifetime and energy-bandgap narrowing in diffused-junction silicon solar cells

The effects of bandgap narrowing, surface recombination and lifetime on the performance of n+p-diffused-junction silicon solar cells are analysed, and experimental results are given to show that the bulk recombination in the n+-diffused region plays an important role in limiting the open-circuit voltage of solar cells. The analysis shows that the surface effects are relatively unimportant in diffused-junction solar cells with surface doping concentration above 1020/cm3 because of the low lifetime due to phonon-assisted recombination in addition to Auger recombination in the heavily doped layer. The analysis also brings out the effects of bandgap-narrowing models and lifetime models on the estimated carrier-concentration distributions, short-circuit currents and open-circuit voltages of solar cells. The theoretical results are compared with the experimental data obtained on n+p solar cells having different n+-layer thicknesses and different surface concentrations, to demonstrate the tenability of the bandgapnarrowing and lifetime models used in the analysis.