Cu2O Solar Cells Research Articles

Semitransparent Cu2O Films Based on CuO Back Layer for Photoelectrochemical Water Splitting and Photovoltaic Applications.

Cuprous oxide (Cu2O) as an intrinsic p-type semiconductor is promising for solar energy conversion. The major challenge in fabricating Cu2O lies in achieving both high transparency and high performance in a tandem device. The Cu2O photocathodes often employ gold as the back contact layer. However, it is not an optimal choice in tandem device due to its poor transmission, scarcity, and electron-hole recombination at the interface of Au and Cu2O. Here, we presented a facile method that utilizes the earth-abundant material copper oxide (CuO) to fabricate highly transparent Cu2O devices. The maximum transmittance of the Cu2O film on CuO (FTO/CuO/Cu2O) increased from 42 % to 58 % compared with Cu2O film on Au (FTO/Au (3 nm)/Cu2O) in 550-800 nm. After coating atomic layer deposition (ALD) layers and hydrogen evolution reaction (HER) catalyst, the photocurrent density at 0 V (versus RHE) of the semitransparent Cu2O photocathode with CuO as the back layer for photoelectrochemical (PEC) water splitting reached -4.9 mA cm-2, which showed a 24.5 % improvement compared with FTO/Au/Cu2O photocathode. Moreover, expanding the CuO layer strategy to the field of solar cells enables Cu2O solar cells to achieve a PCE of 2.37 %.

Design and Simulation of a Cooling System for FTO/I-SnO2/CdS/CdTe/Cu2O Solar Cells

The temperature in solar cells is one of the main factors affecting their efficiency. Increasing the temperature in solar cells reduces efficiency. According to previously published and recently published studies by our team, with increasing temperature in 5-layer FTO/i-SnO2/CdS/CdTe/Cu2O solar cells, the efficiency has decreased by 8.86% per 100 K. In this research, phase change materials have been used to control the temperature in 5-layer solar cells. Our overall goal in this study is to control the temperature in FTO/i-SnO2/CdS/CdTe/Cu2O solar cells to increase their efficiency. The results obtained using simulations and numerical analysis and comparative analysis show that if one layer is used as a cooling arrangement in 5-layer FTO/i-SnO2/CdS/CdTe/Cu2O solar cells, it reduces the surface temperature of solar cells and increases efficiency.

Numerical investigation of the Cu2O solar cell with double electron transport layers and a hole transport layer

In this paper, a model of the Cu2O solar cell with double electron transport layers (ETLs) and a hole transport layer (HTL) has been investigated by SCAPS. Compared to the single ETL of ZnO, the problem of low open circuit voltage of the Cu2O solar cells can be improved by introducing the double ETLs of Zn(O,S)/ZnS. Our simulation results show that the sulfur concentration of Zn(O,S) and the donor density in double ETLs have a significant effect on device performance. The optimum S/S + O ratio and the best donor density are 0.82 and 8 × 1017cm−3, respectively. Due to the formation of an electron reflector and back surface field (BSF), an enhancement in both short circuit current density and open circuit voltage can be realized by introducing an appropriate HTL, and the best HTL is CuI, showing an efficiency of 12.15%. Then, the work function of metal electrode, the Cu2O thickness, the defect density and the acceptor density of Cu2O absorber layer, and the defect density at the Cu2O interfaces have been systematically investigated. After optimization, the best device efficiency of 16.49% can be achieved. Our results have demonstrated a new high-efficiency structure for cuprous oxide solar cells.

Photovoltaic study of TiO2 films sensitized with Cu2O and CdS QDs for applications in a solar cell

The effect of the Cu2O and CdS QD particles on the photoconversion efficiency of the TiO2 solar cell was analyzed. The Cu2O particles were synthesized using the chemical reduction method, and the CdS QDs were prepared using the SILAR method. The JV curves indicated that the photocurrent of the TiO2/ZnS solar cell was 0.04 ​mA/cm2, while the introduction of Cu2O particles in the TiO2/Cu2O/ZnS configuration showed that the cell exhibited a photocurrent forty times higher, of 1.82 ​mA/cm2. With the introduction of CdS QD in the following TiO2/Cu2O/CdS/ZnS and TiO2/CdS/ZnS/Cu2O solar cell configurations, the current increased to 5.34 ​mA/cm2 and 5.57 ​mA/cm2, respectively, being three times higher compared to TiO2/Cu2O/ZnS. Although the values of FF and Voc decreased in the TiO2 solar cells sensitized with Cu2O and CdS, probably due to the introduction of new defects, the photogenerated current increased significantly. These results lead to an improvement in photoconversion efficiency, η=0.38% for TiO2/Cu2O/CdS/ZnS and η ​= ​0.65% for TiO2/CdS/ZnS/Cu2O which is due to an increase in the absorption range. Cu2O particles contribute as a sensitizer probably improves the alignment of the conduction band between the different materials and the defect passivation effect of CdS on the surface of TiO2.

Inorganic Lead‐Free Cs2AuBiCl6 Perovskite Absorber and Cu2O Hole Transport Material Based Single‐Junction Solar Cells with 22.18% Power Conversion Efficiency

AbstractCs2AuBiCl6 is considered to be a potential lead‐free double perovskite alternative for perovskite solar cells. Its electronic and optical properties are investigated using density functional theory. The electronic properties of Cs2AuBiCl6 material ensure a bandgap of 1.40 eV (without considering SOC) and 1.12 eV (with SOC) using mBJ exchange‐correlation functional, close to the optimal bandgap for solar cell application as per the Shockley–Queisser limit. Optical properties suggest a high absorption coefficient ≈105 cm−1 with low reflectance, making it the optimal absorber material. Furthermore, the photovoltaic performance of Cs2AuBiCl6 based single‐junction transparent conducting oxide (TCO)/IDL1/Cs2AuBiCl6/IDL2/Cu2O solar cell is investigated using SCAPS‐1D device simulation program. The impact of electron affinity, thickness, carrier concentration, defect density, and interface defect density is examined using interface defect layer (IDL) on the photovoltaic performance. The maximum photoconversion efficiency (PCE) of ≈22.18% is noticed for optimized material's parameters. These studies on TCO/IDL1/Cs2AuBiCl6/IDL2/Cu2O solar cell will provide guidelines for designing and developing an efficient lead‐free perovskite‐based solar cell as an alternative to conventional halide perovskite materials based solar cell.

Effect of thickness, bandgap, and carrier concentration on the basic parameters of Cu2O nanostructures photovoltaics: numerical simulation study

ABSTRACT There is no clear data about the optimum thicknesses, band gaps, and charge densities of Cu2O thin films to fabricate solar cells. Therefore, here, Solar Cell Capacitance Simulator (SCAPS) program was employed to simulate the Cu2O nanostructures solar cells. Effect of window layer thickness, absorber layer thickness, bandgap, and carrier concentration on basic parameters of Cu2O solar cells were studied. Results revealed that window layer thickness in range from 0.3 to 0.4 µm is optimum to produce a higher performance of about 6.5%. Bandgap should be greater than 2.1 eV and donor carrier concentration under 1×1016 cm-3 are required to improve solar cell efficiency of about 8%. Built-in potential, width of the depletion layer, collection length of charge carrier, lifetime of minority carrier, and recombination rate are the main factors directing performance of devices. Consequently, employing our results to fabricate Cu2O solar cells is a step forward to improve efficiencies.

Elucidating the origin of external quantum efficiency losses in cuprous oxide solar cells through defect analysis

Heterojunction Cu2O solar cells are an important class of Earth-abundant photovoltaics that can be synthesized by a variety of techniques, including electrochemical deposition (ECD) and thermal oxidation (TO). The latter gives the most efficient solar cells of up to 8.1% reported in the literature, but is limited by low external quantum efficiencies (EQE) in the long wavelength range (490–600 nm). By contrast, ECD Cu2O gives higher short wavelength EQEs of up to 90%. We elucidate the cause of this difference by characterizing and comparing ECD and TO films using impedance spectroscopy and fitting with a lumped circuit model to determine the trap density, followed by simulations. The data indicates that TO Cu2O has a higher density of interface defects, located approximately 0.5 eV above the valence band maximum (NV), and lower bulk defect density thus explaining the lower short wavelength EQEs and higher long wavelength EQEs. This work shows that a route to further efficiency increases of TO Cu2O is to reduce the density of interface defect states.

Numerical investigation on efficiency improvement of double layer antireflection coating AZO/buffer/Cu2O/CuO on back-surface fluorine-doped tin oxide heterostructure solar cells

Optical and electrical features of Cu2O solar cells from simple primitive bufferless AZO/Cu2O to complex single/double layer-antireflection coating (S/DLARC) on back-surface fluorine-doped tin oxide (BSF/FTO), were numerically studied. The simulated cells were optimized using a low-conduction band offset buffer, controlled-defect BSF, and antireflection coating layers under a compatible fabrication process. By considering the interlayer defects, the optimized DLARC/AZO/buffer/Cu2O/CuO on BSF/FTO exhibits an improved efficiency of 9.17%, with a JSC≈11.45 mA/cm2, a VOC≈1.191 V, and a fill factor of 67.22% under simulated illumination (AM 1.5G, 100 mW/cm2). Finally, the cell underwent simulated moisturized conditions (RH=90% at T=60°C), where its performance dramatically declined with the exposure time. The results show that the models can be adapted for prediction of the Cu2O-based-cell behavior prior to fabricating.

Optical, structural, and photoelectrochemical properties of nanostructured Cl-doped Cu2O via electrochemical deposition

In this work, we report on the synthesis of cuprous oxide (Cu2O) thin films from sulfate bath on fluorine doped tin oxide glass (FTO/glass) substrates with different concentrations of copper chloride (CuCl2) by electrochemical deposition. The effects of CuCl2 concentrations were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), UV–Vis transmittance, capacitance measurements (i.e., Mott-Schottky (M-S) plots), photocurrent and electrochemical impedance spectroscopy. The measurements of X-rays diffraction (XRD) showed that the Cu2O films are pure and have a monocrystalline structure. The M-S plots demonstrate that the conduction type of the Cu2O films changes with increasing the carrier density by increasing CuCl2 concentration in the deposition bath. Photocurrent measurements confirm that Cl-doped Cu2O films are n-type semiconductors excepted for Cu2O doped with 0.005 M. Changes in the photocurrent response and the electronic disorder were discussed as a function of CuCl2 concentration. It was found that the highest n-type photocurrent density of 0.045 mA/cm2 and the lowest charge transfer resistance (Rct) was obtained when the concentration of CuCl2 was 0.01 M. Carrier density of Cu2O films varied between 1.41 × 1020 to 1.69 × 1020 cm−3 when the CuCl2 concentration was between 0.01 and 0.03 M. The optical measurements show a direct band gap depending on the concentration of CuCl2. The solution based doping method is particularly suitable for large area, low cost, and high throughput fabrication of Cu2O solar cells.

Homojunction Cu2O Solar Cells Fabricated with Various Impurity-Doped Epitaxially Grown n-Type Cu2O Thin Film by Electrochemical Deposition

This paper describes the photovoltaic properties of homojunction Cu2O solar cells fabricated with various impurity-doped epitaxially grown n-type or i-type Cu2O thin films by an electrochemical deposition (ECD) method. Significantly enhanced open circuit voltage (VOC) and conversion efficiency (η) were achieved in AZO/Cu2O:Cl/p-Cu2O:Na and/or AZO/Cu2O:Mn/p-Cu2O:Na homojunction solar cells fabricated by Cu2O:Cl and/or Cu2O:Mn thin films as the n- or i-type layer using ECD; these values were higher than those obtained in AZO/n-ZnO/p-Cu2O heterojunction solar cells. The obtained enhanced Voc and η suggest that the Cu2O:Cl and/or the Cu2O:Mn thin film layers act as an n- or i-type appropriate active layer. The highest Voc, short-circuit current density (JSC), and the conversion efficiencies for AZO/n-type Zn-Ge-O thin film/Cu2O:Mn/Cu2O:Na homojunction solar cells were 0.84 V, 10.1 mA/cm2, and 4.74%, respectively.

Homojunction Cu2O Solar Cells Fabricated with Various Impurity-Doped Epitaxially Grown n-Type Cu2O Thin Film By Electrochemical Deposition

This paper describes the photovoltaic properties of a homojunction Cu2O solar cells fabricated with a various impurity-doped epitaxially grown n-type Cu2O thin-film by electrochemical deposited (ECD) method. The various impurity-doped n-type Cu2O thin film layer was prepared on thermally oxidized polycrystalline p-type sodium-doped Cu2O (p-Cu2O:Na) sheet substrates under various deposition conditions using the following ECD process. Initially, an acetic acid and Copper (II) acetate aqueous solution was prepared with 0.08 M acetic acid, 0.02 M Copper (II) acetate and de-ionized water; then a 0.1-1.0×10-5 M CuCl2, InCl3, CdCl2, ZnCl2 or MnCl2 aqueous solution was added to the solution as a doping impurity; and after that, a 3 M LiOH, NaOH or KOH aqueous solution was added to adjust the pH. Next, a p-Cu2O:Na sheet substrate was immersed in the above solution at a temperature of 60-90 oC; a Pt plate and the p-Cu2O:Na sheet substrate were used as the anode and cathode electrodes, respectively, of the ECD. Finally, the deposition was carried out under various current densities of 0.1-2.0 mA/cm2 for durations of 1-30 min. In addition, various n-type oxide semiconductor, such as GaXAl1-X-O or Zn1-XGeX-O multicomponent oxide thin films and an Al-doped ZnO (AZO) thin film were deposited at room temperature using a pulsed laser deposition or magnetron sputtering methods as the n-type semiconductor layer and the transparent electrode, respectively. The solar cells were fabricated by forming an AZO/n-oxide semiconductor/various impurity-doped n-type Cu2O/p-Cu2O:Na structure on the front surface of the Cu2O:Na sheets and an Au ohmic electrode on the back surface (the sheets function as the active layer as well as the substrate). The photovoltaic properties of the resulting solar cells were measured under AM1.5G solar illumination. For example, the Cu2O homojunction solar cells was fabricated by epitaxialiy growing a Cl-doped Cu2O (Cu2O:Cl) thin film on p-Cu2O:Na (with a hole concentration of 1015-1019 cm-3) sheets by ECD. Significantly enhanced open circuit voltage (VOC) and conversion efficiency (η) were achieved in AZO/n-Cu2O:Cl/p-Cu2O:Na heterojunction solar cells fabricated by Cu2O:Cl thin-film as the n-type layer by using ECD; these values were higher than those obtained in AZO/p-Cu2O and AZO/n-ZnO/p-Cu2O solar cells. The obtained enhanced Voc and η suggest that the Cu2O:Cl thin-film n-type layer acts as an appropriate active layer. In addition, significant improvement of photovoltaic properties was achieved in heterojunction solar cells fabricated with a Ga1-XAlX-O or Zn1-XGeX-O multicomponent oxide thin film n-type semiconductor window layer prepared by optimizing the chemical composition (the Ga or Ge content). Note that the photovoltaic properties obtained in AZO/Ga0.975Al0.025-O or Zn0.38Ge0.62-O/n-Cu2O:Cl/p-Cu2O:Na (with a hole concentration on the order of 1015 cm-3) heterojunction solar cells could be controlled by changing the Cl content doped into the Cu2O:Cl thin film.

Excitonic Effects in Emerging Photovoltaic Materials: A Case Study in Cu2O

Excitonic effects account for a fundamental photoconversion and charge transport mechanism in Cu2O; hence, the universally adopted “free carrier” model substantially underestimates the photovoltaic efficiency for such devices. The quasi-equilibrium branching ratio between excitons and free carriers in Cu2O indicates that up to 28% of photogenerated carriers during photovoltaic operation are excitons. These large exciton densities were directly observed in photoluminescence and spectral response measurements. The results of a device physics simulation using a model that includes excitonic effects agree well with experimentally measured current–voltage characteristics of Cu2O-based photovoltaics. In the case of Cu2O, the free carrier model underestimates the efficiency of a Cu2O solar cell by as much as 1.9 absolute percent at room temperature.

All-oxide solar cells based on electrodeposited Cu2O absorber and atomic layer deposited ZnMgO on precious-metal-free electrode

All-oxide solar cells based on electrodeposited p-type Cu2O absorber and atomic layer deposited n-type ZnMgO are investigated. The introduced solar cell architecture is free of precious metals that are usually employed as electrodes in Cu2O solar cells and is composed almost exclusively of oxide layers. Firstly, a detailed investigation is made on the potentiostatic electrodeposition of the absorber layer on the sputtered, highly conductive and reflective Cr/ITO (ITO: tin-doped indium oxide) electrode. The focus is set on adjusting the deposition parameters to obtain Cu2O layers, which are void-free and with large grains. A multi-textured film is obtained with prominent (111), (200) and (220) reflections. The absorber has a bandgap of 1.93eV and a rough, antireflective surface. Next, the n-type ZnMgO layer has been investigated and a linear relation of the optical bandgap (3.2–3.9eV) versus Mg content was found. The valence band maximum levels have been extracted from X-Ray photoelectron spectroscopy and the band alignment of the Cu2O/ZnMgO was evaluated. Solar cells employing ZnMgO films with ~10at% Mg show best photovoltaic performance, whereas for larger Mg contents a dramatic decrease of the performance takes place, presumably due to excessive, deep-level defects, leading to tunnel recombination. Best cells show short circuit current density of 6.8mA/cm2, open circuit voltage of 550mV, fill factor of 45% and power conversion efficiency of 1.67%.

Oxygen deficiency and Sn doping of amorphous Ga2O3

The potential of effectively n-type doping Ga2O3 considering its large band gap has made it an attractive target for integration into transistors and solar cells. As a result amorphous GaOx is now attracting interest as an electron transport layer in solar cells despite little information on its opto-electrical properties. Here we present the opto-electronic properties, including optical band gap, electron affinity, and charge carrier density, for amorphous GaOx thin films deposited by pulsed laser deposition. These properties are strongly dependent on the deposition temperature during the deposition process. The deposition temperature has no significant influence on the general structural properties but produces significant changes in the oxygen stoichiometry of the films. The density of the oxygen vacancies is found to be related to the optical band gap of the GaOx layer. It is proposed that the oxygen deficiency leads to defect band below the conduction band minimum that increases the electron affinity. These properties facilitate the use of amorphous GaOx as an electron transport layer in Cu(In,Ga)Se2 and in Cu2O solar cells. Further it is shown that at low deposition temperatures, extrinsic doping with Sn is effective at low Sn concentrations.

Photoresponse enhancement of Cu2O solar cell with sulfur-doped ZnO buffer layer to mediate the interfacial band alignment

It is promising that the efficiency of cuprous oxide (Cu2O) based heterojunction solar cell can be improved by inserting a buffer layer to mediate the energy alignment at the interface. In this work, a sulfur-doped ZnO (ZnOS) buffer layer with properly tuned band alignment was introduced to the Cu2O heterojunction solar cell with Al-doped ZnO (AZO) as the n-type transparent conductive oxide layer to form an interfacial energy barrier, which improved the open-circuit voltage extremely. The experimental parameters including the oxygen pressure, buffer layer thickness and the deposition temperature were optimized. The mechanism of buffer layer was investigated, which revealed the rise of conduction band minimum of ZnOS buffer layer, thereby mitigating the interfacial recombination. This work shed light on the optimization of the interfacial band alignment of heterojunction solar cell, improving the photoresponse property.

Heteroepitaxial Cu2O thin film solar cell on metallic substrates.

Heteroepitaxial, single-crystal-like Cu2O films on inexpensive, flexible, metallic substrates can potentially be used as absorber layers for fabrication of low-cost, high-performance, non-toxic, earth-abundant solar cells. Here, we report epitaxial growth of Cu2O films on low cost, flexible, textured metallic substrates. Cu2O films were deposited on the metallic templates via pulsed laser deposition under various processing conditions to study the influence of processing parameters on the structural and electronic properties of the films. It is found that pure, epitaxial Cu2O phase without any trace of CuO phase is only formed in a limited deposition window of P(O2) - temperature. The (00l) single-oriented, highly textured, Cu2O films deposited under optimum P(O2) - temperature conditions exhibit excellent electronic properties with carrier mobility in the range of 40–60 cm2 V−1 s−1 and carrier concentration over 1016 cm−3. The power conversion efficiency of 1.65% is demonstrated from a proof-of-concept Cu2O solar cell based on epitaxial Cu2O film prepared on the textured metal substrate.

Fabrication of homojunction Cu2O solar cells by electrochemical deposition

Homostructural Cu2O solar cells were fabricated with consecutive electrochemical depositions of a p-Cu2O thin film and a n-Cu2O layer on a transparent conductive substrate. The parameters of growth Coulomb number for n-type and p-type Cu2O films, which determine the film thickness of Cu2O, were fine-tuned to investigate their effects on the performance of homojunction solar cells. According to XRD and SEM analyses, the crystalline structure and the optimum thickness of Cu2O films were accomplished at growth Coulomb numbers 0.135C for n-Cu2O and 0.208C for p-Cu2O. Significantly, the best performance of the homojunction Cu2O cell achieved conversion efficiency 0.42% with Voc=0.42V, Jsc=2.68mAcm−2 and FF=0.38. This work hence demonstrates that the proposed strategy to improve the performance of solar cells realized by electrochemical deposition has the potential to produce cheap and environmental friendly solar cells.

Perspective: Maintaining surface-phase purity is key to efficient open air fabricated cuprous oxide solar cells

Electrochemically deposited Cu2O solar cells are receiving growing attention owing to a recent doubling in efficiency. This was enabled by the controlled chemical environment used in depositing doped ZnO layers by atomic layer deposition, which is not well suited to large-scale industrial production. While open air fabrication with atmospheric pressure spatial atomic layer deposition overcomes this limitation, we find that this approach is limited by an inability to remove the detrimental CuO layer that forms on the Cu2O surface. Herein, we propose strategies for achieving efficiencies in atmospherically processed cells that are equivalent to the high values achieved in vacuum processed cells.

Solution-processed high-haze ZnO pyramidal textures directly grown on a TCO substrate and the light-trapping effect in Cu2O solar cells

We have prepared pyramidally textured ZnO (PT-ZnO) films with a high light-scattering effect using a simple low temperature (75 °C) solution process that involved no annealing and vacuum processes. The PT-ZnO films, which were composed of dense ZnO columnar grains with a (101)-faceted pyramidal tip, were formed directly on a TCO substrate by electrodeposition. The electrodeposition was performed within 10 min from Zn(NO3)2 aqueous solutions that contained NaCl; during deposition, a two-step electrolytic current was applied to separately control the nucleation density and grain size of ZnO grains. Light-scattering effects from the pyramid structure were examined by measuring haze values in the visible region and comparing the results with those from planar and nanorod structures. The PT-ZnO films showed a haze value of ∼52%, which is 3.7 and 2.2 times higher than those of planar and nanorod ZnO films, respectively. On the basis of total transmittance and haze, the optimal thickness of the pyramidal textures was determined to be 0.7–1.2 μm. Theoretical simulation of light scattering on the PT-ZnO was performed using a simple geometric model which indicated that the refraction angle, path length and intensity of transmitted light vary significantly depending on the outer refractive index of ZnO. The light-trapping effect derived from the PT-ZnO was demonstrated by fabricating ZnO/Cu2O thin-film solar cells. The Cu2O solar cell using the PT-ZnO showed efficient light absorption, achieving a 1.3 times higher short circuit current density than that using the planar ZnO.

Annealing Effects of Sputtered Cu2O Nanocolumns on ZnO‐Coated Glass Substrate for Solar Cell Applications

Cuprous oxide (Cu2O) films were prepared on an indium tin oxide glass substrate by radiofrequency magnetron sputtering using a high‐purity Cu target. The temperature of annealing was varied to obtain Cu2O thin films with various elements, compositions, and surface structures. The p‐Cu2O thin films thus formed were characterized by FESEM and XRD. After annealing at 500∘C, the bilayer structure which consisted of Cu nanoclusters on the surface of a film of Cu2O nanocolumns was observed. The Cu2O solar cell with the bilayered structure exhibited poor power conversion efficiency.