External Quantum Efficiency of Electrochemically Prepared and Annealed Directly Stacked SLG/GZO/Cu2O/CuO Photoactive Layer

Abstract

A strategy to enhance the copper-oxides-based photovoltaic’s performance is to introduce p-type semiconductor layers with different bandgap energies into the photoactive layer to extend the absorption bands and to increase the quantum efficiency. In this research, the strategy has been realized by a directly stacked Cu2O/CuO photoactive layer that utilizes both copper oxides as light-absorbing layers. The directly stacked Cu2O/CuO photoactive layers were fabricated with a novel facile method of rapid thermal annealing (RTA) of the Cu2O samples (prepared by electrodeposition) in air at temperatures of 473-673 K. EQE performance of directly stacked Cu2O/CuO shows widened absorption span at wavelengths above 630 nm under biased voltage was attributed to the light conversion from not only the Cu2O layer but also the CuO layer. Widened absorption edge from 630 to 850 nm can be confirmed further from UV-vis characterization as a result of the formation of the directly stacked layers. Although the XRD patterns show insignificant changes between different annealing temperatures, FE-SEM observation indicates the formations of the CuO layer on the Cu2O layer at approximate thicknesses of 20∼150 nm. In spite of the EQE values are still low, further improvements can be implemented. However, this research highlights that both Cu2O and CuO layers act as light-absorbing layers. This is proving the validity of the directly stacked Cu2O/CuO photoactive layer in increasing the rate of electron-hole generation through expanded wavelength absorption, which provides insight into future designs of high-performance photoactive layers.