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Mg x Zn 1-x O (MZO) has recently gained popularity as a transparent electron contact in CdTe-based solar cells. The value of the conduction band offset (CBO) and, hence, of the MZO bandgap are often considered essential parameters of this interface, as—in theory—the CBO has a strong impact on both the conduction of electrons and the recombination of holes. However, in this contribution, we report MZO/CdSeTe interfaces where recombination appears to be independent of the CBO. The implications of such results are discussed.

In this contribution, we investigate why different dopant species and back-contact architectures lead to different sub-bandgap behaviors in CdSeTe solar cells. Through extraction of the absorptance from photoluminescence spectra, we parse the contributions from material properties and from cell optics. We show that, as expected, arsenic doping leads to an increase in sub-bandgap features over traditional copper doping, and that this is a material property of arsenic-doped CdSeTe. Conversely, the increase in sub-bandgap absorption and emission using alternative back contact architectures can be attributed to the cell optics, and more specifically to the increased reflectance of the back interface, leading to at least a doubling of the pathlength for sub-bandgap photons.