Defect Structure and Photovoltaic Characteristics of Internally Stacked CuO/Cu₂O Photoactive Layer Prepared by Electrodeposition and Heating

Abstract

The internally stacked CuO/Cu 2 O photoactive layers were prepared by electrodeposition of the Cu 2 O layer followed by heating in air. The 1.4 eV-p-CuO layer was heteroepitaxially grown on the Cu 2 O layer accompanied by the formation of nanopores by heating at 573 K, and both the CuO and Cu 2 O layers possessed excellent semiconductor qualities with band-edge emission in the visible light region. The internally stacked CuO/Cu 2 O photoactive layer revealed the photovoltaic performance in a corresponding wide photon energy range due to the utilization of the photovoltaic ability for both the CuO and Cu 2 O layers by applying a bias voltage. Heating at 673 K induced transfer of the thickened CuO layer to the polycrystalline phase and coalescence of nanopores, resulting in the disappearance of the light emission and photovoltaic performance, irrespective of the bias voltage. The crystal and semiconductor qualities for both the CuO and Cu 2 O layers affected the photovoltaic performance for the internally stacked CuO/Cu 2 O photoactive layer.

Modification of large area Cu2O/CuO photocathode with CuS non-noble catalyst for improved photocurrent and stability

“…However, the most performing overlayers often rely on poorly scalable or expensive fabrication techniques such as atomic layer deposition (ALD) 4 , 14 , 15 , allowing the deposition of a few-nanometer thick layer, highly conformal and optically transparent. A different approach relies on the exploitation of simple and affordable routes such as thermal or chemical treatments that would result in the formation of the different heterostructures (Cu 2 O/C 12 , Cu 2 O/CuO 17 – 25 , Cu 2 O/CuS 26 , Cu 2 O/TiO 2 27 , Cu 2 O/NiO 28 ). Among those, one of the simplest yet effective is the oxidation of Cu or Cu 2 O, through which a surface layer of cupric oxide CuO (~ 1.3–1.8 eV bandgap) is obtained, forming a staggered band alignment with the underneath cuprous oxide.…”

Photoelctrochemically Fabricated and Heated Cu2O/CuO Bilayers with Enhanced Photovoltaic Characteristics

“…Copper oxides of Cu 2 O and CuO are p-type semiconductors with the band gap energies of 2.1 and 1.4 eV, and both have been applied as photovoltaic layers in oxide solar cells, − and as photocathodes to generate hydrogen gas by photoelectrochemical water splitting. − Also, p-Cu 2 O/p-CuO bilayers have attracted increasing attention as photoactive layers which satisfy the aforementioned multi-band gap strategy to enhance the performance. − The Cu 2 O and CuO layers had been prepared by several techniques of thermal oxidation of metallic Cu, , gas-phase deposition processes such as sputtering and pulsed laser deposition, , and solution chemical processes which include electrochemical processes. − The Cu 2 O/CuO bilayers have been prepared by several ways composed of chemical preparations followed by heating, , and the improved photovoltaic and photocathode characteristics have been demonstrated for those prepared by the Cu 2 O electrodeposition followed by subsequent thermal oxidation in air. , The Cu 2 O/CuO bilayers showed a widened photovoltaic wavelength range originating from both the Cu 2 O and CuO layers, but the external quantum efficiency (EQE) was low, compared to those for the single Cu 2 O and CuO layers. , The introduction of nanopores into the Cu 2 O layer and structural change in the grains of the CuO layer were brought forth by heating, which pose detrimental effects on the photovoltaic characteristic . In the case of electrochemical fabrication of a Cu 2 O/CuO bilayer in a copper­(II)–lactate complex aqueous solution, the challenge lies not in the initial electrodeposition of Cu 2 O layer but in the subsequential electrodeposition of the CuO layer, which needs electrons, which are the minority carriers in the underlying Cu 2 O layer.…”

“…24−26 The Cu 2 O/CuO bilayers have been prepared by several ways composed of chemical preparations followed by heating, 27,28 and the improved photovoltaic and photocathode characteristics have been demonstrated for those prepared by the Cu 2 O electrodeposition followed by subsequent thermal oxidation in air. 17,18 The Cu 2 O/CuO bilayers showed a widened photovoltaic wavelength range originating from both the Cu 2 O and CuO layers, but the external quantum efficiency (EQE) was low, compared to those for the single Cu 2 O and CuO layers. 29,30 The introduction of nanopores into the Cu 2 O layer and structural change in the grains of the CuO layer were brought forth by heating, which pose detrimental effects on the photovoltaic characteristic.…”

High-Resolution Mapping of Local Photoluminescence Properties in CuO/Cu2O Semiconductor Bi-Layers by Using Synchrotron Radiation

“…It has been pointed out that photoluminescence and photovoltaic properties are affected by the presence of lattice defects, such as vacancies and impurities in semiconductor materials and devices [ 4 , 6 ]. Moreover, in multi-layered film semiconductor devices that possess complex heterogeneous structures, local variations of photovoltaic properties are expected to accompany heterogeneity and lack of lattice defects.…”

“…The CuO/Cu 2 O bi-layer is a potential candidate material for high-performance photoactive material for solar cells, as well as for photocathodes to generate hydrogen by photoelectrochemical water splitting. The bi-layer includes two p-type semiconductors with different bandgap energies, which is a strategy to realize a high-performance photovoltaic layer by extending the photovoltaic wavelength range and improving the quantum efficiency [ 6 ]. Since the photovoltaic performance is highly dependent on its semiconductor quality, which affects carrier transportation and recombination loss [ 6 ], the importance of local photoluminescence that allows the investigation of local semiconductor quality is evident.…”