The combination of two solar cells with a suitable combination of two different band gaps allows for a more efficient harvesting of the solar spectrum. Therefore, such tandem solar cells are perceived as the photovoltaic devices of the future. One realization of this device concept uses a high efficiency amorphous/crystalline (a-Si:H/c-Si) heterojunction solar cell as bottom cell, while the top cell consists of a cell based on a perovskite absorber, as sketched below.
The a-Si:H/c-Si heterojunction cell is a well-established technology with a demonstrated world record single-junction power conversion efficiency η > 25%, and η > 20% for cells routinely processed at HZB. The perovskite cells, on the other hand, constitute the cutting edge of current thin-film PV research, due to their recently demonstrated high efficiencies above 20% and ease of fabrication.
The PhD thesis will explore this perovskite/silicon tandem cell concept. The student will work in close collaboration with members from both the a-Si:H/c-Si and the organic PV/perovskite groups to design, implement and characterize thin films with the desired properties into solar cell architectures, using state of the art deposition and characterization tools. The experimental work will be complemented by optical and electrical modelling of the cell's layer stack, which will serve to understand the experimental results as well as to find optimum cell designs and to calculate the ultimate efficiency limits of devices with realistic materials properties. This work is also expected to provide key contributions to HZB's efforts in the European project MESO, and the PhD candidate will collaborate with other members of the international MESO project team, such as the Snaith group at the University of Oxford/UK.