Defect Engineering in Cuprous Oxide (Cu₂O) Solar Cells

Abstract

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 105-109).This thesis is focused on the development of a cuprous oxide (Cu₂O) thin-film (TF) solar cell that is fabricated by manufacturing-friendly methods such as electro-deposition, sputtering and atomic layer deposition. Due to its bandgap of close to 2 eV, it has the potential of being applied as top cell in a tandem configuration. Firstly, I perform bottom-up cost and price analysis to investigate the economic feasibility of TF and c-Si based tandem photovoltaic modules. Next, I investigate the formation of good ohmic back contacts on Cu₂O absorber layer and demonstrate that low contact resistivity can be achieved with a variety of metals on heavily doped Cu₂O films by forming a tunnel junction. Then, I apply synchrotron-based X-ray absorption spectroscopy (XAS) to characterize two front contact buffer materials: amorphous Zn-Sn-O (a-ZTO) and Sndoped Ga₂O₃. I elucidate a fundamental loss mechanism in the amorphous Zn-Sn-O (a-ZTO) electron-blocking layer that has origin in local structural disorder and establish the structure-process- property relationship of a-ZTO so that the front buffer layer can be optimized for photovoltaics. Then, I investigate the doping mechanism of Sn dopant atoms in TFs and single crystalline Ga₂O₃:Sn by revealing the doping mechanism so that Ga₂O₃:Sn can be optimized for photovoltaics. Lastly. I apply bulk defect engineering to manipulate the intrinsic point defect structure of Cu₂O towards improved device performance. The key results will inform the processing conditions for improving mobility and minority carrier lifetime in Cu₂O. Keywords - Earth-abundant, thin-film solar cells, tandem, defect engineering, cost modeling, synchrotron.by Sin Cheng Siah.Ph. D