Improved Heterojunction Quality in Cu(2)O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn(1-x)Mg(x)O

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn(1-x)Mg(x)O thin films onto p-type thermally oxidized Cu(2)O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu(2)O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu(2)O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu(2)O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu(2)O interface. Optimization of AP-SALD conditions as well as keeping Cu(2)O away from air and moisture in order to minimize Cu(2)O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn(1-x)Mg(x)O/Cu(2)O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu(2)O-based photovoltaics.