Junction studies on electrochemically fabricated p–n Cu2O homojunction solar cells for efficiency enhancement

Abstract

p–n Cu₂O homojunction solar cells were electrochemically fabricated by consecutively depositing an n-Cu₂O layer on a p-Cu₂O layer. In order to better understand the Fermi levels of the electrochemically grown polycrystalline p- and n-Cu₂O layers and maximize the overall cell performance, the back and front contacts of the Cu₂O homojunction cells were systematically changed and the I–V characteristics of the resulting cells were examined. The result shows that the intrinsic doping levels of the electrochemically prepared p-Cu₂O and n-Cu₂O layers are very low and they made almost Ohmic junctions with Cu metal with which previously studied p-Cu₂O layers prepared by thermal oxidation of Cu foils are known to form Schottky junctions. The best cell performance (an η of 1.06%, a V_OC of 0.621 V, an I_SC of 4.07 mA cm^–2, and a fill factor (ff) of 42%) was obtained when the p-Cu₂O layer was deposited on a commercially available ITO substrate as the back contact and a sputter deposited ITO layer was used as the front contact on the n-Cu₂O layer. The unique features of the p–n Cu₂O homojunction solar cell are discussed in comparison with other Cu₂O-based heterojunction solar cells.