Optimizing Cu2O-MgxZn1-xO heterojunction photovoltaic material
Authors:Jianchi Chen, Samantha Wilson
Mentor:Harry Atwater, Howard Hughes Professor and Professor of Applied Physics and Materials Science, California Institute of Technology
In the photovoltaic (PV) industry, a less costly alternative photovoltaic material is needed for the further progress of PV industry. Cu2O is a non-toxic, earth abundant material with a 2.1eV direct band gap and is well known as a suitable photovoltaic material. Recent study showed that by depositing ZnMgO alloy thin films on to Cu2O substrate, photovoltaic with potential of efficiency improvement can be made, but the composition and the manufacture process here still need to be optimized. We hypothesized that by adjusting the Magnesium composition in the thin film, we can tune the optical and electrical properties of ZnMgO thin films, so that we can find the best fit for the Cu2O substrate and maximize the energy-transition efficiency. In the study, we made ZnMgO thin films using radio-frequency sputtering and controlled the Magnesium composition of the films by adjusting the power added on the Mg-containing target. We then explored the electro-optical properties of the films we manufactured using approaches such as X-ray diffractometry, transmission measurement, X-ray photoelectron spectroscopy. We first verified that the Magnesium composition of the sputtered film is proportional to the power percentage on the Mg-containing target. Then our study of lattice constants, band gap energies, and valence band shows that all three of these properties possess linear relationship with the variation of the Mg-composition. We further applied this result into the study of Cu2O-ZnMgO solar cells, and made Cu2O-ZnMgO devices that are photo-active and shows improved open-circuit voltage and efficiency. This results of this study can be used to the photovoltaic industry, for the optimization and mass production of Cu2O-ZnMgO devices, which are made of only earth abundant materials, and thus have the potential of being more monetarily profitable and efficient than current photovoltaic materials.