LabAdviser/Technology Research/Technology for CZTS-Silicon Tandem Solar Cells
Fabrication of surfaces for the promotion of bacterial biofilms
- Project type: PhD project
- Project responsible: Alireza Hajijafarassar
- Supervisors: Ole Hansen, Jörg Hübner, Anders Michael Jørgensen
- Partners involved: DTU Fotonik
- Project start: 2017-06-01
- Thesis: https://orbit.dtu.dk/en/projects/technology-for-czts-silicon-tandem-solar-cells
Project description
Satisfying the demand for renewable friendly energy is one of the urgent grand challenges. Photovoltaics (PV) is definitely one of the answers to this challenge. Since the efficiency of single material PV cells is approaching fundamental limits, a major challenge in photovoltaics today is to improve efficiency in order to reduce the levelized cost of electricity below that of fossil fuels. As a result, for production of PV modules with higher efficiencies, tandem (multijunction) approches have been introduced. The key benefit of a multijunction solar cell lies in exploiting the solar spectrum in a more efficient manner. In a double-junction cell architecture, the high energy photons are harvested in the top sub-cell with higher bandgap, while the low energy photos are harvested in the lower bandgap bottom sub-cell. Consequently, higher open circuit voltages (Voc) can be achieved due to lower thermalization losses of charge carriers. Silicon-based tandem structure can be exceptional candidates for further improving the efficiency while leveraging the well-established existing crystalline silicon manufacturing capacity. Ideally, the top sub-cell on the silicon (with band gap of 1.1 eV) should possess a bandgap of 1.6-1.9 eV. However, within this range, there are a limited number of materials that can exhibit high open circuit voltages. There has been efforts on utilizing methylammonium-lead-halide perovskite as the absorber layer of the top sub-cell. Even though high efficiencies have been reported in the literature3,4, the technology suffers from fast degradation of the perovskite material as well as incorporation of toxic elements such as lead (Pb). On the other hand, CZTS (Cu2ZnSnS4) material consisting of inexpensive, non-toxic elements with a band gap of 1.45 eV can also be a potential candidate for such a cell. The theoretical limit for a CZTS cell is close to 27 %. However, the current efficiency of CZTS is 9.5 % obtained by UNSW, but this value is expected to continue rising as a result of efforts in the solar cell community.
This PhD project is part of a larger effort at DTU Nanotech and DTU Fotonik, i.e. the ALTCELL project, which aims at developing the necessary technology to realize the potential for enhanced efficiency by integrating a Cu2ZnSnS4 (CZTS) solar cell on top of a silicon solar cell. The project is supported by the “Innovationsfonden” (PI, Jørgen Schou, DTU Fotonik) and is carried out with international (Nanyang Technological University, Singapore) and industrial (e.g. Haldor Topsøe A/S) partners. This PhD project is partly funded by “Innovationsfonden” and partly by DTU Nanotech.
The ultimate goal of the overall project is to develop technology for a CZTS-Silicon tandem solar cell. This entails an improvement of CZTS single cell technology to enhance the efficiency, development of a suitable silicon bottom cell, and solving issues related to integration of the two cells.
This PhD project will be involved in all three main topics by:
1. Providing some of the front and back end films for the CZTS cell, participation in characterization of the CZTS films, whereas the actual synthesis of CZTS will mostly be done by other project partners.
2. Developing and characterizing the bottom silicon cell. The developed cell has to be suitable for the tandem structure and compatible with the CZTS layer.
3. Developing technology for tunnel/barrier layers between the two absorber layers will be the decisive innovation for the construction of such a cell. The purpose of these layers are twofold: 1) at the interface electron currents from the silicon cell must be transformed into hole currents in the CZTS cell. 2) The interface must have a diffusion barrier to protect the silicon cell from in-diffusion of metals (particularly Cu) from the CZTS. This is a particularly challenging task.
Publications
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Fabrication: Process flows
This fabrication process flow is used for the fabrication of the silicon bottom cell.
Process flow (word format):