UBC Theses and Dissertations

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UBC Theses and Dissertations

Optoelectronics with two-dimensional atomic crystals Pashaei, Parham


Two-dimensional materials are attractive choices for photovoltaic applications due to their unique material properties. Their extremely high absorption-to-thickness ratio supersedes conventional semiconducting crystals and their transparency and flexibility open new possibilities in photovoltaic applications. More importantly, van der Waals stacking allows the building of multi-stack solar cells. Several reports have demonstrated the potential of these materials for photovoltaic applications. However, the total efficiency of monolayer photovoltaic devices remains low. In this report, properties of multi-layer photovoltaic devices based on a van der Waals heterostructure diode are investigated. Our annealing method in ultra-high vacuum shows up to ~4x increase in current and our low-vacuum measurements show improvement in current and noise. Low-temperature measurement at 77K is conducted to understand the underlying working mechanism and for further explanation of photovoltaic behavior. These results are compared with reports of single-layer-based heterostructure photovoltaic diodes with similar conditions showing higher current density. To achieve these results, we optimize a process to produce exfoliated two-dimensional materials in a high-purity glovebox, design and build a stacking setup to fabricate heterostructures and optimize nanofabrication and measurement methods. Finally, we investigate the outlook for future devices by proposing NPN heterostructures. These findings open new discussions for further development of photovoltaic devices based on two-dimensional materials.

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