Abstract
Cuprous oxide (Cu2O) homojunction thin films on Ti substrates were fabricated by an electrochemical deposition in which a p-Cu2O layer was deposited on an n-Cu2O layer by carefully controlled bath conditions. It was found that the open-circuit voltage of the homojunction solar cell was significantly influenced by the pH of the lactate bath. The variation of the pH was used to achieve the best possible crystal orientation for homojunctions. The crystallinity and morphology of the products were characterized by X-ray diffraction (XRD), high-energy x-ray diffraction (HEXRD), and scanning electron microscopy (SEM). The current density voltage (J-V) analysis showed that the sulfur treatment and annealing enhanced the photocurrent by ten-fold compared to the untreated and unannealed homojunction solar cell. X-ray photoelectron spectroscopy (XPS) studies confirmed that the sulfur treatment eliminated the surface CuO and formed a thin layer of CuS, which was very useful to make the front Ohmic contact. Transient measurements confirmed that the p-type Cu2O layer, which was subjected to sulfur treatment, significantly reduced the recombination, thus enhancing the efficiency of the solar cell. The best sulfur treated annealed Ti/n-Cu2O/p-Cu2O/Au solar cell produced an energy conversion efficiency of 2.64% with an open-circuit voltage of 490 mV and a short circuit current density of 12.8 mA cm−2 under AM 1.5 illumination.
Highlights
The increasing global demand for energy, limited fossil fuel supplies on the planet, and global climate changes due to greenhouse gas emissions from fossil fuel burning have made it necessary to use renewable, clean energy sources as energy alternatives
The highest conversion efficiency achieved with cuprous oxide (Cu2 O) as the active layer is 8.1% with a MgF2 /Al-doped ZnO/Zn0.38 Ge0.62 -O/Cu2 O:Na p-n heterostructure, showing that further studies are necessary to push the efficiency of Cu2 O-based solar cells toward their theoretical efficiency, which is about 20% [4,5]
These photoelectrochemical cell (PEC) experiments were performed in an electrolytic solution containing 0.1 M of sodium acetate at room temperature (25 ◦ C), by potentiostatically biasing at 0 V of the Cu2 O homojunction photoelectrode and directly feeding the current output of the potentiostat to the Keithley 2100 multimeter
Summary
The increasing global demand for energy, limited fossil fuel supplies on the planet, and global climate changes due to greenhouse gas emissions from fossil fuel burning have made it necessary to use renewable, clean energy sources as energy alternatives. P-n heterojunction solar cell structures require p-type and n-type semiconductors, which should have proper energy level alignment to improve charge separation and reduce electron-hole recombination. This requirement restricts the choice of selecting the two semiconductor materials. Wang et al reported the fabrication of Cu2 O p-n homojunctions Their properties as potential solar cell devices have not been addressed [10]. Han et al fabricated a Cu2 O p-n homojunction solar cell with a conversion efficiency of 0.1% by electrochemical growth of a p-type Cu2 O film using a lactate bath on an n-type Cu2 O film, which was grown using an acetate bath [11]. Sulfur treatment and annealing were successfully used to improving the efficiency of Ti/n-Cu2 O/p-Cu2 O/Au solar cells
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