Elucidating efficiency losses in cuprous oxide (Cu₂O) photovoltaics and identifying strategies for efficiency improvement

Abstract

In this thesis, I fabricated and characterized a series of thin-film cuprous oxide (Cu₂O) photovoltaic devices. I constructed several different device designs, using sputtered and electrochemically deposited Cu₂O. Characterization was done using XRD, SEM, optical spectroscopy, quantum efficiency, current-voltage, and capacitance-voltage measurements. Then, these devices were modeled using SCAPS-1D, a numerical simulation package, as well as MATLAB for analytical solutions. This simulation enabled a quantitative breakdown of efficiency losses in Cu 20 devices. Simulations suggest that low device efficiencies of 0.3-0.6% may be explained in part by poor bulk transport properties in the Cu₂O. However, the predominant efficiency loss comes from an unoptimized p-n heterojunction, in which a large negative conduction band offset and structural defects lead to a low built-in voltage and high recombination activity. The effects of interface engineering are demonstrated in experiment and simulation. Broader simulations suggest opportunities for future efficiency improvements towards 10%. These include the improvement of bulk properties, the selection of alternative pairing materials, novel device structures, and the possibility of multijunction cells.