Interfacial Defect Control for Infrared Conversion Widening of Silicon Single-Crystal Solar Cells

A multi-interface solar cell design exploiting the parts of solar spectrum heretofore never converted by single-crystal silicon devices seems to be possible with local material modifications combined with a superimposition of hetero-interface transition zones. Possible structural modifications by implantation of a silicon single-crystal target causes a series of “secondary” effects of basic importance from the photovoltaic conversion point of view. The 1800 nm divacancy infrared band activity has revealed totally unknown behavior in the built-in strain field of the inserted α-Si/c-Si hetero-interface. First, even an annealing temperature of 770 K is not enough to quench the divacancy absorption. Next, the elimination of useful band-tail and useless divacancy activities is not coincident, i.e. divacancy absorption can be quenched without too much reduction of the band-tail activity. A relatively important infrared current could be observed experimentally up to 2500 nm and by extrapolation up to about 3500 nm.