Ultrathin Resonant-Cavity-Enhanced Amorphous Germanium Solar Cells on ZnO Honeycomb Electrodes

Ultrathin resonant-cavity-enhanced solar cells based on less than 30 nm thick hydrogenated amorphous germanium (a-Ge:H) absorbers have the potential to replace standard micrometer-thick microcrystalline silicon absorbers in silicon thin-film solar cell technology, as they yield comparable infrared absorption. Combined with the concept of a folded solar cell on a three-dimensional structured ZnO honeycomb electrode, grown in a cost-effective scalable electrochemical process, the strong absorption of this ultrathin type of cell can be even further enhanced. Our results show an increase of 11% in the short-circuit current density of an a-Ge: H solar cell on a honeycomb electrode compared to a flat reference cell, with no detrimental effects in the electrical properties. The benefit in the optical performance is mainly related to a broadband increase in the quantum efficiency due to an increased absorber volume as well as suppressed interferences inside the front electrode. At the same time, the desired resonances inside the resonant-cavity-enhanced solar cell itself are maintained.