LabAdviser/Technology Research/Technology for CZTS-Silicon Tandem Solar Cells: Difference between revisions
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= | ==Preface== | ||
This PhD project was part of a larger effort at DTU Nanotech and DTU Fotonik, 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 was supported by the “Innovationsfonden” (PI, Jørgen Schou, DTU Fotonik) and was 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 Nanolab. | |||
The ultimate goal of the overall project was 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. | |||
The PhD project was involved in all three main topics by: | |||
1. Providing some of the front and back end films for the CZTS cell, participation in the 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. | |||
3. Developing technology for tunnel/barrier layers on the silicon 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. | |||
==Project description== | ==Project description== | ||
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In this thesis, we chose CuZnSnS4, a quaternary compound semiconductor with a bandgap of 1.5 eV, as a promising non-toxic, earth-abundant, and cheap representative candidate from the chalcogenide family, and systematically studied the integration challenges with silicon. For this purpose, we developed and optimized a thermally resilient silicon cell structure with polysilicon carrier selective contacts, and used an ultrathin (< 10 nm) titanium nitride-based diffusion barrier at the interface of the two cells (called the “barrier layer”) to protect the silicon cell against contamination. Throughout the thesis, we showed that the performance of the CZTS-Si tandem devices heavily relies on the electrical, optical, and protection behavior of the barrier layer. By proper engineering of the TiN and polysilicon interfacial layers, we managed to keep the silicon cell almost intact during the full fabrication of CZTS, and demonstrated a world-record efficiency of 4.1% for this type of structure. Our findings implicate that the growth of new materials, with a wide range of thermal budgets and compositions, is technically feasible on silicon. Moreover, we believe that our proposed tandem structure may provide new insights for the Si community in terms of device architecture engineering for future silicon-based tandem cells. | In this thesis, we chose CuZnSnS4, a quaternary compound semiconductor with a bandgap of 1.5 eV, as a promising non-toxic, earth-abundant, and cheap representative candidate from the chalcogenide family, and systematically studied the integration challenges with silicon. For this purpose, we developed and optimized a thermally resilient silicon cell structure with polysilicon carrier selective contacts, and used an ultrathin (< 10 nm) titanium nitride-based diffusion barrier at the interface of the two cells (called the “barrier layer”) to protect the silicon cell against contamination. Throughout the thesis, we showed that the performance of the CZTS-Si tandem devices heavily relies on the electrical, optical, and protection behavior of the barrier layer. By proper engineering of the TiN and polysilicon interfacial layers, we managed to keep the silicon cell almost intact during the full fabrication of CZTS, and demonstrated a world-record efficiency of 4.1% for this type of structure. Our findings implicate that the growth of new materials, with a wide range of thermal budgets and compositions, is technically feasible on silicon. Moreover, we believe that our proposed tandem structure may provide new insights for the Si community in terms of device architecture engineering for future silicon-based tandem cells. | ||
==Publications in peer-reviewed journal papers== | ==Publications in peer-reviewed journal papers== | ||