Al2O3, Au, and Ni were deposited as front layers on the opposite side of the back contact. The back contact layer was covered with Teflon tape, and the Cu2O substrate was placed in the ALD chamber for Al2O3 deposition. Trimethylaluminum (Strem Chemicals, 98 %) was used as the precursor for Al2O3. For the Al2O3 layer, the reaction chamber temperature was maintained at 120 °C, while the precursor was kept at room temperature. The valve of Al2O3 deposition was opened for 0.1 s, followed by a 6.0 s N2 purge. Subsequently, a 0.1 s pulse of H2O was introduced, followed by another 6.0 s N2 purge. This cycle was repeated 13 times to get a 1 nm-thick Al2O3 layer. Following the ALD process, a 100 nm Au layer and a 50 nm Ni layer were sequentially deposited using a magnetron sputtering method (EM ACE600, Leica).