Theory of the electrical and photovoltaic properties of polycrystalline silicon

Grain boundary states play a dominant role in determining the electrical and photovoltaic properties of polycrystalline silicon by acting as traps and recombination centers. The recombination loss at grain boundaries is the predominant loss mechanism in polycrystalline solar cells. Cell parameters are calculated based on a transformation of grain boundary recombination centers to a uniform distribution of such states throughout the grain. Effective carrier lifetime is expressed in terms of grain size, allowing calculation of short-circuit current, open-circuit voltage, and fill factor. Excellent agreement is observed between theory and experiment for almost all device parameters. It is indicated that one could fabricate 10% efficiency polycrystalline solar cells from 20-μm-thick material if the grain size exceeds 500 μm.