Optically enhanced tandem a-Si solar cells

The viability of incorporating specular thin-film stacks within a tandem a-Si alloy solar cell for the enhancement of power conversion efficiency has been demonstrated. The design strategy for optical enhancement layers was to reduce interface reflection losses and improve the transmission of incident light to the bottom junction. As a measure of the expected improvement in power conversion efficiency, the gain in short-circuit current of the bottom cell due to the inclusion of enhancement layers in the top cell was computed. For most designs, the improvement in short-circuit current was significant. The predictions of the optical model were verified by fabricating a top solar cell structure and incorporating a back contact. The predicted short-circuit current gain was 33.84% relative to an analogous device without optical enhancement layers.