Defects improve solar cell efficiency

The group, from the University’s Department of Physics found that the strain gradient (i.e. inhomogenous strain) in the solar cells, through physical force or induced during the fabrication process, can prevent photo-excited carriers from recombining, leading to an enhanced solar energy conversion efficiency.

Most commercial solar cells are formed of two layers creating at their boundary a junction between two kinds of semiconductors, p-type with positive charge carriers (electron vacancies) and n-type with negative charge carriers (electrons). When light is absorbed, the junction of the two semiconductors sustains an internal field splitting the photo-excited carriers in opposite directions, generating a current and voltage across the junction. Without such junctions the energy cannot be harvested and the photo-excited carriers will simply quickly recombine eliminating any electrical charge.

The Warwick group used an epitaxial thin film of BiFeO3 grown on a LaAlO3 substrate to determine the impact of inhomogenous deformation on the film’s ability to convert light into electricity by examining how its strain gradient affects its ability to separate photo-excited carriers.