Abstract
Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O 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 Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.
Highlights
Cuprous oxide (Cu2O) is an earth-abundant non-toxic p-type semiconductor material[1]
These include etching of the substrates in dilute nitric acid to remove any cupric oxide (CuO) after oxidation as well as after the evaporation of the golden electrode, minimizing the time substrates spend in open air before the Zn1-xMgxO deposition and deposition of Zn1-xMgxO on Cu2O substrates by Atmospheric pressure spatial atomic layer deposition (AP-SALD)
The advantage of AP-SALD compared to conventional atomic layer deposition (ALD) is that films can be grown outside a vacuum with a growth rate that is one to two orders of magnitude higher
Summary
Cuprous oxide (Cu2O) is an earth-abundant non-toxic p-type semiconductor material[1]. This allows the metal oxide film to grow layer by layer. We show how tuning the conditions for depositing zinc oxide and zinc magnesium oxide films on thermally oxidized cuprous oxide substrates allowed for improved interface quality and better solar cell performance to be obtained. This improvement was made possible through the identification of the major limiting factor in Cu2O based solar cells: recombination at the heterojunction interface due to an excessive formation of cupric oxide (CuO) on the Cu2O surface
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