Abstract
Heterojunction solar cells were fabricated by electrochemical deposition of p-type, cuprous oxide (Cu2O) absorber on sputtered, n-type ZnO layer. X-ray diffraction measurements revealed that the as-deposited absorber consists mainly of Cu2O, but appreciable amounts of metallic Cu and cupric oxide (CuO) are also present. These undesired oxidation states are incorporated during the deposition process and have a detrimental effect on the photovoltaic properties of the cells. The open circuit voltage (VOC), short circuit current density (jSC), fill factor (FF) and power conversion efficiency (η) of the as-deposited cells are 0.37 V, 3.71 mA/cm2, 35.7% and 0.49%, respectively, under AM1.5G illumination. We show that by thermal annealing in vacuum, at temperatures up to 300 °C, compositional purity of the Cu2O absorber could be obtained. A general improvement of the heterojunction and bulk materials quality is observed, reflected upon the smallest influence of the shunt and series resistance on the transport properties of the cells in dark and under illumination. Independent of the annealing temperature, transport is dominated by the space-charge layer generation-recombination current. After annealing at 300 °C the solar cell parameters could be significantly improved to the values of: VOC = 0.505 V, jSC = 4.67 mA/cm2, FF = 47.1% and η = 1.12%.
Highlights
Cuprous oxide (Cu2O) is one of the first known semiconducting materials
Heterojunction solar cells were fabricated by electrochemical deposition of p-type, cuprous oxide (Cu2O) absorber on sputtered, n-type ZnO layer
X-ray diffraction measurements revealed that the asdeposited absorber consists mainly of Cu2O, but appreciable amounts of metallic Cu and cupric oxide (CuO) are present
Summary
Cuprous oxide (Cu2O) is one of the first known semiconducting materials. its photovoltaic (PV) property was very early recognized [1], the technological advancements towards a Cu2O-based solar cell were only sporadic. The demand is to turn from bulk to thin film absorbers, which require significantly less material and lower fabrication cost To this end, ECD of Cu2O has a large potential as it takes place close to room temperature (about 50−60 ◦C) and from aqueous solution. Annealed solar cells present increased shunt resistance and lower series resistance, suggesting improvement of the heterojunction interface and absorber’s bulk. The combination of these effects leads to the enhancement of the short circuit current, open circuit voltage and fill factor of the heterojunction solar cells
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