Cu2O-based Solar Cells Research Articles

A review of Cu2O solar cell

Cu2O-based solar cells offer a promising solution to address future energy challenges due to their affordability, eco-friendliness, and impressive power conversion efficiency (PCE). With the development of thin film deposition technology, the maximum PCE of single-junction solar cells fabricated based on Cu2O is 9.5%. Because the spectral sensitivity overlaps between Cu2O and crystalline silicon (c-Si) is small, Cu2O thin-film solar cells can be made into tandem solar cells with Si-based solar cells to achieve higher PCE. The Cu2O–Si tandem solar cell has been delivered 24.2% PCE in 2020, a time when the PCE of stand-alone silicon solar cells was 17.6%. The purpose of this paper is to summarize the development of Cu2O-based heterojunction, homojunction. The Cu2O material properties, n and p-type doping, the role of defects and impurities in bulk of films or at the interface of the p–n-junction and n-type buffer layer on the performance of Cu2O-based heterojunction like ZnO–Cu2O, and the difficulty in decreasing the interface state and doping in Cu2O homojunction solar cells are discussed. This review discusses the Cu2O film material preparation method, the history of Cu2O based solar cells, the essential factors required to enhance the performance of various types of Cu2O-based solar cells, and the potential future research opportunities for as a top subcells in Cu2O–Si tandem solar cells.

Cu2O Heterojunction Solar Cell with Photovoltaic Properties Enhanced by a Ti Buffer Layer

In this study, semiconductor oxide cuprite (Cu2O) and indium tin oxide (ITO) heterojunction solar cells with and without a 10 nm thick titanium (Ti) thin film as the buffer layer were fabricated and characterized for comparison. The Cu2O film was formed by low-cost electrodeposition, and Ti and ITO layers were deposited on a glass substrate by sputtering. The interfacial microstructures, surface topology, and electrical and photovoltaic properties of both solar cells were investigated. The test results showed that the Ti buffer layer changed the surface morphology, resistivity, and contact potential of the electrodeposited Cu2O film. With these changes, the photovoltaic performances of the Cu2O/Ti/ITO solar cell including open-circuit voltage (VOC) and short-circuit current (ISC) were all enhanced compared to the Cu2O/ITO solar cell, and the power conversion efficiency was improved from 1.78% to 2.54%. This study offers a promising method to improve the efficiency of Cu2O-based solar cells for sustainability in material resource, environment and eco-system, and energy production.

Comparative analysis of the substitutional and interstitial Li-, Na-doped, and Li∖Na-Codoped Cu2O via density functional calculations

A comprehensive comparative study utilizing HSE06 and GGA density functional calculations was conducted to investigate the impact of Li and Na doping, as well as their co-doping, on the physical properties of cuprous oxide (Cu2O). This study examined three possible structures, including substitution of Li, Na, and Li/Na for Cu, and interstitial Li, Na, and Li/Na in both tetrahedral and octahedral sites. The results of the study revealed that the introduction of alkaline atoms leads to structural changes in Cu2O, and the degree of lattice parameter extension or compression varies across different doping sites. Additionally, the study provided an estimation of the enthalpies of formation for pure and doped-Cu2O, which is useful in understanding the stability of the systems. Notably, the study found that Li, Na, and Li/Na-doped-Cu2O were more readily formed in substitutional sites rather than in interstitial sites. The findings also indicate that substitutional doping and co-doping exhibit a large band gap while maintaining the properties of a p-type semiconductor, while interstitial doping and co-doping of Cu2O led to significant absorption enhancement and n-type conductivity characteristics. These results provide new insights into the structural and electronic properties of Cu2O, with the findings suggesting that interstitial doping of Li and Na could be a promising approach for improving the absorption of visible light in Cu2O-based solar cells, thus contributing to the development of more efficient and cost-effective photovoltaic devices.

Numerical modeling and analysis of AZO/Cu2O transparent solar cell with a TiO2 buffer layer

In the present work, titanium dioxide (TiO2) is sandwiched as a buffer layer between n-type aluminum-doped zinc oxide (AZO) and p-type cuprous oxide (Cu2O), increasing the efficiency of metal oxide-based solar cells. The effects of the device parameters such as thicknesses, carrier concentrations, and defect densities were investigated by numerical simulation to obtain optimal performance of Cu2O-based solar cells. Our findings reveal that by the incorporation of TiO2 thin film, the efficiency of the solar cell increases remarkably from 2.54 to 5.02 %. The optimal thicknesses of the Cu2O and TiO2 layers are in the range of 10 μm and 0.1 μm, respectively. We obtained optimal photo-electric conversion efficiency of 10.17 % and open-circuit voltage of 1.35 V while achieving 8.90 mA/cm2 short-circuit current density and 84.12 % fill factor, using structure parameters of 0.2 μm AZO, 0.1 μm TiO2 and 10 μm Cu2O with optimal acceptor-type dopant density in Cu2O of 1E17 cm−3 and donor-type dopant density in TiO2 of 1E18 cm−3.

Cuprous Oxide (Cu2O) Based Solar Cell Thickness Dependence

The rapid advancement of devices that transform light into other energy forms has led to the growth of various solar cell structures established on silicon and other compound semiconductors. Photovoltaic devices that are efficient are required to ensure solar power's competitiveness with traditional energy sources. The most intriguing phase of copper oxides is Cu2O. There have been several findings of Cu2O-based solar cells; nevertheless, their efficiencies are quite minimal due to charge recombination at the crystal boundary and other factors. The goal of the present study is to review the effect of Cu2O thin film thickness prepared by oxidation techniques on efficiency, and then previous related work was systematically studied to investigate their structural and morphological properties. Gravimetric measurements were used to determine the thickness of Cu2O on Cu. The XRD pattern presented shows a single phase of Cu2O with no obvious impurity peaks. The finding shows that when the thickness is 26.30µm, the conversion efficiency is high; image analysis from a different method of deposition demonstrated that the films were compact throughout the entire sample surface, with no observed pinholes. The morphology of the stratum was strongly dependent on the deposition techniques.

Reduced bandgap and enhanced p-type electrical conduction in Ag-alloyed Cu2O thin films

The photovoltaic absorber Cu2O has attracted much interest in recent years because it is a nontoxic, earth-abundant, and low-cost p-type semiconductor. To date, Cu2O-based solar cells have achieved a power conversion efficiency of ∼8%. However, this value is still far below its theoretical power conversion efficiency of ∼20%. Further improvement in the photovoltaic properties is believed, at least in part, to be limited by its poor p-type electrical conductivity and its relatively wide bandgap (∼2.17 eV). Herein, we studied the electrical and optical properties of Ag alloyed-Cu2O thin films. We demonstrated that the bandgaps of Cu2O can be decreased by Ag-alloying, which is confirmed by density functional theory calculations indicating that the bandgap reduction is due to the downshift of the conduction band minimum in Cu2O, while the valence band edge of Cu2O remains unchanged. Additionally, we found that p-type carrier concentrations are dramatically enhanced in Ag alloyed-Cu2O thin films. Such interesting behavior may be due to the reduced activation energy for hole transport caused by Ag-alloying. This work suggests that Ag incorporation may be a promising and practical method to improve the photovoltaic performance of high efficiency Cu2O-based solar energy conversion.

Surface modification and stoichiometry control of Cu2O/SnO2 heterojunction solar cell by an ultrathin MgO tunneling layer

Here, we demonstrated the potential of an ultrathin Mg-rich MgO tunneling layer as a passivation layer for earth-abundant Cu2O based solar cell. An ultrathin Mg-rich MgO layer was introduced to the interface of Cu2O/SnO2 heterojunction by electron beam evaporation, which greatly enhanced the efficiency of Cu2O/SnO2 heterojunction solar cell. The MgO layer was found to significantly reduce the CuO defect density and create a stoichiometry Cu2O surface confirmed by high-resolution X-ray photoelectron spectroscopy. Thus, charge recombination caused by interface defect was mitigated bringing an increased device efficiency. This work highlights the need for stoichiometric Cu2O surface in Cu2O-based solar cells.

Progress of Cu2O/ZnO oxide heterojunction solar cells

Recent progress of low cost Cu2O/ZnO hetero-junction solar cells is reviewed in this paper. The Cu2O used as an absorbing layer in photovoltaic cells is a direct bandgap semiconductor, exhibiting natural p-type conductivity. The source material of Cu2O-based solar cells is abundant and environmentally friendly. The main device structure of Cu2O/ZnO solar cells presents a planar and nano-wire/nano-rod configuration. The nanostructured Cu2O architecture conduces to charge collection in the device. The planar Cu2O absorbing layer with large grain size, achieved through the thermal oxidation of Cu sheets, exhibits high quality of the Cu2O/ZnO solar cells. The interface buffer layer (like i-ZnO, a-ZTO and Ga2O3) and back surface field (BSF, such as p+-Cu2O) can effectively improve energy band alignment match and increase carrier transport. The Cu2O paired with a 10-nm-thick Ga2O3 layer provides a nearly ideal conduction band offset and thus reduces the interface recombination. The Ga2O3 is a highly suitable buffer layer for enhancing the Voc (Voc value reaches 1.2 V) and conversion efficiency of Cu2O-based solar cells. The p+-Cu2O like N-doped Cu2O (Cu2O:N) and Na-doped Cu2O (Cu2O:Na) can reduce back-contact resistance and create an electron-reflecting back surface field in the Cu2O based solar cells. When a p-type Cu2O: Na acts as an absorbing layer and a zinc-germanium-oxide (Zn1-xGex-O) thin film is used as an n-type layer (buffer), Cu2O hetero-junction solar cell with the device structure MgF2/Al-doped ZnO (ZnO:Al)/Zn0.38Ge0.62-O/Cu2O:Na shows an efficiency of 8.1%. The oxide hetero-junction solar cells have a great potential application in the future photovoltaic field.

Two dimensional modeling of Cu2O heterojunction solar cells based-on β-Ga2O3 buffer

Despite the advantages of cuprous oxide (Cu2O) as a cheap, abundant, non-toxic, and sustainable photovoltaic material, defects and conduction band offset (CBO) at the Cu2O heterojunction interfaces are still the most challenges to achieve higher efficiencies. In this study, a Cu2O heterojunction solar cell based on a β-Ga2O3 buffer has been modeled and simulated using Silvaco TCAD. The model exactly matches the reported experimental results of open circuit voltage (VOC) and short current density (JSC) characteristics and well reproduces the fill factor (FF) and efficiency, η, of a fabricated solar cell within ±2% tolerance. By using the model, we explored a novel structure for higher efficiency solar cell by adding an interface and a defective layer. It was found that the associated defects and traps to each layer significantly influence the electrical and optical characteristics of the solar cell performance. The model shows an external quantum efficiency (EQE) more than 0.6, an FF greater than 68% and an η about 5.44% under the AM1.5 illuminations. Furthermore, the model shows that it can be used generously to investigate the parameters of the Cu2O-based solar cells with different buffers prior to fabricate.

Cu2O-based solar cells using oxide semiconductors

We describe significant improvements of the photovoltaic properties that were achieved in Al-doped ZnO (AZO)/n-type oxide semiconductor/p-type Cu2O heterojunction solar cells fabricated using p-type Cu2O sheets prepared by thermally oxidizing Cu sheets. The multicomponent oxide thin film used as the n-type semiconductor layer was prepared with various chemical compositions on non-intentionally heated Cu2O sheets under various deposition conditions using a pulsed laser deposition method. In Cu2O-based heterojunction solar cells fabricated using various ternary compounds as the n-type oxide thin-film layer, the best photovoltaic performance was obtained with an n-ZnGa2O4 thin-film layer. In most of the Cu2O-based heterojunction solar cells using multicomponent oxides composed of combinations of various binary compounds, the obtained photovoltaic properties changed gradually as the chemical composition was varied. However, with the ZnO-MgO and Ga2O3-Al2O3 systems, higher conversion efficiencies (η) as well as a high open circuit voltage (Voc) were obtained by using a relatively small amount of MgO or Al2O3, e.g., (ZnO)0.91–(MgO)0.09 and (Ga2O3)0.975–(Al2O3)0.025, respectively. When Cu2O-based heterojunction solar cells were fabricated using Al2O3–Ga2O3–MgO–ZnO (AGMZO) multicomponent oxide thin films deposited with metal atomic ratios of 10, 60, 10 and 20 at.% for the Al, Ga, Mg and Zn, respectively, a high Voc of 0.98 V and an η of 4.82% were obtained. In addition, an enhanced η and an improved fill factor could be achieved in AZO/n-type multicomponent oxide/p-type Cu2O heterojunction solar cells fabricated using Na-doped Cu2O (Cu2O:Na) sheets that featured a resistivity controlled by optimizing the post-annealing temperature and duration. Consequently, an η of 6.25% and a Voc of 0.84 V were obtained in a MgF2/AZO/n-(Ga2O3–Al2O3)/p-Cu2O:Na heterojunction solar cell fabricated using a Cu2O:Na sheet with a resistivity of approximately 10 Ω·cm and a (Ga0.975Al0.025)2O3 thin film with a thickness of approximately 60 nm. In addition, a Voc of 0.96 V and an η of 5.4% were obtained in a MgF2/AZO/n-AGMZO/p-Cu2O:Na heterojunction solar cell.