The influence of heavy doping effects on silicon solar cell performance

Many modern crystalline silicon solar cells are highly doped in both the emitter and the so-called back-surface-field (BSF) structure. Auger recombination and band-gap narrowing thus take place in these regions with detrimental effects on cell performance. Through a design study is has been shown that these effects negate the benefits of the BSF structure if the latter contains a layer doped to a higher concentration than about 1017 cm−3, and that the primary benefit of the BSF structure is to permit the use of a thinner base region rather than to provide higher efficiency. For the emitter, a high dopant surface concentration is seen to be beneficial when the surface recombination velocity is high. However, to realize the cell performance gains potentially available from reducing the surface recombination velocity and the saturation current contribution from the base requires a reduction of the emitter dopant surface concentration. Attempts to obtain more than 20% (AM 1.5) efficiency will require the almost complete elimination of heavy doping effects through reducing the impurity concentration in the emitter.