Electrical characterization of interface recombination and its dependence on band offset, potential barrier height, and inversion in certain heterojunction solar cells

The open-circuit voltage V_OC of a heterojunction solar cell of the generic TCO/buffer/absorber/back-contact structure is sensitively influenced by the interface recombination at the buffer/absorber front interface R^i,f and at the absorber/back-contact interface R^i,b. We describe an experimental method to separate and quantify these interface recombination rates and the bulk recombination rates from the dependencies of V_OC on temperature and illumination with varying wavelength. We show that R^i,f is mainly determined by the potential barrier height φ_b0 at the buffer/absorber interface. We discuss strategies to increase φ_b0 by engineering band offset, band bending, and inversion.