*1: Toshiba survey.
*2: Nature Energy 2, 17032 (2017)
*3: A solar cell using a compound semiconductor composed of a group III element (gallium, aluminum, indium, etc.) and a group V element (arsenic, phosphorus, nitrogen, etc.)
*4: A method to expose the copper plate to plasma while oxygen flows into the vacuum chamber of the film forming apparatus, causing the copper to react with the oxygen atoms to form the Cu2O layer.
*5: Appl. Phys. Lett. 119, 242102 (2021); https://doi.org/10.1063/5.0072310