Solar Energy Conversion Devices Research Articles

Surface structure of MOVPE-prepared As-modified Si(100) substrates

In the pursuit of high-efficiency tandem devices for solar energy conversion based on III-V-semiconductors, low-defect III-V nucleation on Si(100) substrates is essential. Here, hydrogen and arsenic are key ingredients in all growth processes with respect to industrially scalable metalorganic vapor phase epitaxy. Our study provides insight into Si(100) surface preparation for the initial stage of III-V nucleation. The samples investigated, prepared on substrates with different offcut angles, show single domain surfaces consisting of rows of preferentially buckled dimers. Low energy electron diffraction and reflection anisotropy spectroscopy confirm well-defined (1 × 2)/(2 × 1) majority domains. Fourier-transform infrared spectroscopy revealed hydrogen bonding to the surface dimers, while no impurities were found by XPS. Density functional theory calculations support the experimental results and reveal a novel surface motif of H-passivated Si-As mixed dimers.

Open-Cage Copper Complexes Modulate Coordination and Charge Transfer.

This study presents a novel copper-based redox shuttle that employs the PY5 pentadentate polypyridyl ligand in a dye-sensitized solar cell (DSSC). The [Cu(PY5)]2+ complex exhibits a unique five-coordinate square pyramidal geometry, characterized by a strategically labile axial position, to facilitate efficient dye regeneration while minimizing electron recombination, thereby enhancing DSSC performance. Notably, the inclusion of 4-tert-butylpyridine (TBP) as an additive is shown to significantly modulate the electrochemical and photophysical properties of the copper complexes, attributed to its coordination to the vacant axial site. This interaction leads to an improved open-circuit voltage and overall device efficiency, with the complexes achieving promising efficiencies under standard solar irradiance. The findings underscore the potential of utilizing copper-based redox shuttles with designed ligand geometries to overcome the limitations of current DSSC materials, opening new avenues for the design and optimization of solar energy conversion devices. This work not only contributes to the fundamental understanding of the behavior of copper complexes in DSSCs but also paves the way for future research aimed at exploiting the full potential of such geometrical and electronic configurations for the development of more robust and efficient solar energy solutions.

Enhanced OER performance by varying Al-WO3 electrocatalyst thickness: Process optimization

Oxygen evolution reactions (OER) are highly significant and play a critical role in the advancement of fuel cells, electrolyzers, chemicals, and solar energy conversion devices. The challenge in the quest is attributed to the absence of an efficient electrocatalyst assembly that functions optimally. A simple method of electrodeposition of Al:WO3 on a fluorinated tin oxide (FTO) electrode was used to investigate the OER in this study. The electrodepositions were achieved by employing a three-electrode cell at various scan rates ranging from 10 to 100 mV/s. During this investigation, the influence of the scan rate on electrocatalyst loadings and the impact of electrocatalyst layer thickness on the OER were examined. The electrodepositions of Al:WO3@FTO were analyzed using a range of optical, chemical, and physical techniques such as SEM, XRD, FT-IR, Raman spectroscopy, EDX, EDS mapping, and electrochemical tests. The FTIR and Raman analysis confirmed the synthesis of AL:WO3 while the peaks detected at angles 38.7° and 43° by XRD with planes (111) and (200), served as a distinctive characteristic for identifying aluminum (Al). The peaks observed at angles of 27.8°, 30.7°, 33°, 50.45°, and 58° correspond to WO3 material. The characterization techniques also confirmed that the synthesized material is highly crystalline in nature. The OER potential using Al:WO3@FTO electrodes with different electrocatalyst thicknesses, ranging from 8 nm to 31 nm was investigated by studying various electrochemical techniques such as CV, LSV, CPE, Tafel slope, HP2P splitting, EIS, TOF, short and long-term electrode stability, and double layer capacitance. The linear regression coefficient (R2) was also calculated to measure the relationship between the electrocatalyst's thickness and each electrochemical test. The findings indicated that increasing the scan rates resulted in thinner and denser electrodepositions on the FTO substrate as the thinnest film was formed at 100 mV/s. An inverse relationship between electrocatalyst layer thickness and OER activity was observed. The electrode with the thinnest and most compact electrocatalyst layer, specifically ED Al:WO3@FTO08, exhibited the lowest onset potential of 1.48 V and a maximum current of 84 mA/cm2 at 1.76 V. It also demonstrated superior reaction kinetics, as evidenced by its lower Tafel slope value of 49 mV/dec, which is the lowest among all the electrodes that were prepared. In particular, the electrode with a thin and compact electrocatalyst layer worked better in OER operations than the other five electrodes that had higher amounts of Al:WO3.

Performance comparison of air source heat pump coupling with solar evacuated tube water heater and that with micro heat pipe PV/T

Air source heat pump (ASHP) has been generally regarded as energy saving devices for winter heating, yet for low-income households, the operational costs for heating in low-temperature conditions may be prohibitively high. Solar evacuated tube water heater (SETWH) and photovoltaic/thermal are economical solar energy conversion devices. Integrating them into ASHP has been proven globally to significantly reduce heating costs. However, a performance comparison between the SETWH combined with ASHP (SETWH-ASHP) and of micro heat pipe photovoltaic/thermal (MHP-PV/T) combined with ASHP (MHP-PV/T-ASHP) heating systems remains unexplored. Therefore, for a 120 m2 building with underfloor heating water pipe, SETWH-ASHP and MHP-PV/T-ASHP heating systems were respectively developed on the TRNSYS software platform. Their accuracy was confirmed using prior experimental data, followed by performance simulation for the heating season. The result is that MHP-PV/T-ASHP heating system outperformed SETWH-ASHP heating system, showing a 19 % increase in solar fraction, a 2.2 boost in system energy efficiency ratio, a 12.3 % rise in primary energy saving rate, a 0.9-year shorter payback period, and a reduction of 494.7 kg in CO2 emissions over the heating season. The results offer practical guidance for the promotion and application of heating systems that combine efficient and low-cost solar conversion devices with ASHP.

Multivariable degradation modeling and life prediction using multivariate fractional Brownian motion

In system prognostics and health management, multivariable degradation models have been widely developed to predict the life of complex systems using degradation data of multiple Performance Characteristics (PCs). Recent studies have detected a Long-Term Memory (LTM) effect among the degradation process of various PCs, implying a strong coupling phenomenon between the future degradation behavior and historical degradation trajectory. Although the LTM has been widely integrated into single-PC-based degradation modeling, it has not been considered in multi-PC-based scenarios. To capture LTM among multiple PCs, this article proposes a novel LTM-integrated Multivariate Degradation Model (MDM) for system life prediction based on multivariate fractional Brownian motion, which simultaneously incorporates the cross-correlation among different PCs. To estimate parameters of the LTM-integrated MDM, a maximum likelihood method is developed. Two likelihood-ratio hypothesis tests are developed to test the existence of the overall and individual LTM effect among multiple PCs. Both simulation studies and physical experiments on the performance degradation of solar energy conversion and storage devices are conducted to validate the proposed model. Results reveal that the proposed LTM-integrated MDM significantly outperforms existing MDMs in life prediction, while the lifetime uncertainty is heavily underestimated by those traditional approaches that neglect the LTM.

Designing Atomic Interface in Sb2S3/CdS Heterojunction for Efficient Solar Water Splitting.

In the emerging Sb2S3-based solar energy conversion devices, a CdS buffer layer prepared by chemical bath deposition is commonly used to improve the separation of photogenerated electron-hole pairs. However, the cation diffusion at the Sb2S3/CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb2S3/CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb2S3/CdS heterojunction with an ultrathin Al2O3 interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd2+ cations into the Sb2S3 layer. As a result, a water-splitting photocathode based on Ag:Sb2S3/Al2O3/CdS heterojunction achieves a significantly improved half-cell solar-to-hydrogen efficiency of 2.78% in a neutral electrolyte, as compared to 1.66% for the control Ag:Sb2S3/CdS device. This work demonstrates the importance of designing atomic interfaces and may provide a guideline for the fabrication of high-performance stibnite-type semiconductor-based solar energy conversion devices.

Ultrahigh power factor and excellent solar efficiency in two-dimensional hexagonal group-IV–V nanomaterials

The mesmerizing physical properties of two-dimensional (2D) nanomaterials have resulted in their enormous potential for high-power solar energy conversion and long-term stability devices. The present work systematically investigated the fundamental properties of monolayered 2D group-IV–V materials using a combined approach of first-principles calculations and Boltzmann transport theory, specifically the thermoelectric and optical properties, for the first time. The structural and lattice dynamics analysis disclosed the energetic, dynamical, and mechanical stabilities of 17 out of 25 considered materials. The electronic properties’ calculation shows that all the stable materials exhibit a semiconducting nature. Additionally, the energy–momentum relation in a few systems reveals the quartic Mexican-hat-like dispersion in their valence band edges. Owing to the larger depth of Mexican-hat dispersion and the larger height of density step function modes, the hole carrier mobilities of SnN (761.43 m2/Vs), GeN (422.80 m2/Vs), and SiN (108.90 m2/Vs) materials were found to be significantly higher than their electron mobilities at room temperature. The achieved high Seebeck coefficient and electrical conductivity at room temperature result in excellent thermoelectric power factors for GeN (3190 mW/mK2), SiN (1473 mW/mK2), and CAs (774 mW/mK2) materials, manifesting their potential for thermoelectric devices. Further, the calculated optical and solar parameters demonstrate an exceptionally high value (27.25%) of theoretical limits of power conversion efficiency for the SnBi material, making it a suitable candidate as a light-absorbing material in solar cell devices. The present theoretical work filters out the potential 2D group-IV–V materials for solar and heat energy-harvesting devices.

Study on photochemistry and component transport coupling processes of azobenzene molecular solar thermal system

Molecular solar thermal (MOST) system is a new technology to collect, transform and store solar energy. The mechanism of photochemical reaction and component transport of molecular photoswitches in the reactor is still unclear. In this paper, a simulated theoretical framework for energy conversion rate and energy storage efficiency of solar energy collection and conversion devices based on a molecular solar thermal system was presented. The mathematical model of the photochemical reaction studied was based on an azobenzene derivative, which acted as a molecular photoswitch that can store energy by the switch of molecular structures. The microscopic parameters of reactants were obtained by quantum mechanics calculation and applied to the macroscopic energy conversion analysis of reaction processes. The theoretical framework can predict the conversion and energy storage efficiency of photoisomerization reactions, and can be used for component transport analysis, energy conversion analysis and reaction rate contribution analysis in reactors. We focused on the influence of macroscopic factors, including the flow velocity, inlet reactants concentration and reactor size on the photoisomerization energy storage process. The results of the theoretical analysis were in good agreement with those of existing laboratory equipment. The relative error of the conversion rate is only 0.71% in the photostable state, and the maximum relative error of the conversion rate is 10.99% in the whole process. In addition, in the photochemical reaction, we introduced the concept of absorbance field for the absorbance attenuation caused by the absorption of photons in the medium, so that the local material conversion, absorbance and energy conversion of this type of photochemical reaction can be more clearly understood. This simulated theoretical framework allows the study of molecules in a macroscopic setting, thereby establishing a link between practical engineering and basic chemistry, and providing guidance for the design of molecular solar thermal systems in the future.

Flake-like SnS anchored on the carbon layer for supercapacitor electrode with photo-responsive capacitance enhancement

Photo-responsive supercapacitors incorporate light-responsive materials on capacitive electrodes, making them capable of solar energy conversion and storage within single device. Herein, composite structures consisting of flake-like stannous sulfide (SnS) anchored on a carbon layer (CL) covered nickel foam (CL@SnS/NF) are synthesized as photo-responsive supercapacitor electrode for capacitance enhancement under visible light. SnS as a light-absorbing layer has a narrow bandgap that matches well with the wavelength of visible light, while CL serves as an electron transport channel for effective separation of photogenerated carriers. Due to the synergetic effect of two components above, the areal specific capacitance of the CL@SnS/NF electrode increases from 15.7 to 21.0 mF·cm−2 in light conditions under 0.1 mA·cm−2, which is 1.7 and 6.6 times larger than that of CL/NF and SnS/NF electrodes under the same conditions, respectively, indicating the remarkable light-induced capacitance enhancement performance. The CL@SnS/NF electrode also presents higher photocurrent and photovoltage than two single electrodes, implying its excellent photosensitivity. In addition, the assembled CL@SnS/NF-based symmetric supercapacitor exhibits great capacitance gain under illumination (185.8% at 50 µA·cm−2) and excellent capacitance maintenance (87.7% over 6000 cycles). This work supplies a novel strategy to the development of high-performance solar energy conversion and storage devices.

Soiling in Solar Energy Systems: The Role of the Thresholding Method in Image Analysis

The use of image analysis has often been suggested as a practical way to monitor the soiling accumulated on the surfaces of solar energy conversion devices. Indeed, the deposited soiling particles can be counted and characterized to calculate the area they cover, and this area can be converted into an energy loss. However, several particle counting methodologies exist and can lead to dissimilar results. This work focuses on the role of thresholding, an essential step where particles are distinguished from a background based on the pixel brightness. Sixteen automatic thresholding methods are assessed using 13 200 micrographs of glass coupons soiled at nine locations globally. In low‐to‐intermediate soiling conditions, the “Triangle” method is found to return the minimum coefficient of variation and a mean deviation closer to zero. On the other hand, methods assuming a bimodal distribution of pixel brightness underestimate the area coverage. In addition, since soiling can be unevenly distributed over a surface, different loss estimations can be returned when the same image analysis process is used on different spots on a sample's surface. For these reasons, image analysis should be repeated at multiple locations on each investigated surface.

Optoelectronic enhancement of photocurrent by cyanobacteria on sustainable AP-VPP-fabricated PEDOT electrodes

Photosynthetic microrganisms, including cyanobacteria, can be interfaced with electrodes in biophotovoltaic devices (BPVs) for solar energy conversion. Effective BPV electrodes need to be conductive, transparent, flexible, biocompatible and environmentally friendly, while also being cost-effective, abundant in material and lightweight. The utilisation of electrically conducting polymers (CPs), particularly poly(3,4-ethylenedioxythiophene) (PEDOT) fabricated by an atmospheric pressure vapor phase polymerisation (AP-VPP) technique, is a promising avenue for BPV applications. However, challenges remain in optimising their performance as CPs are dynamic optoelectronic materials, and their interaction with photosynthetic biocatalysts under a range of conditions has not been explored thoroughly. Here we show that AP-VPP PEDOT electrodes hold promise for interfacing with cyanobacteria in BPVs to generate green electricity under red and blue light and moderate applied potentials with exogenous electron mediators. The highest non-mediated photocurrent achieved was 0.48 µA cm−2, with a two-layer PEDOT electrode at 0.5 V applied potential and blue light. The highest mediated photocurrent achieved was 2.73 µA cm−2, with a one-layer PEDOT electrode at 0.3 V applied potential and blue light and the exogenous electron mediator 2,6-dichloro-1,4-benzoquinone (DCBQ). The proposed approach to fabricating PEDOT electrodes offers a new pathway for developing sustainable electrodes for BPVs and pinpoints strategies for future optimisation for achieving high-performance outcomes.

Multiphase Chemistry under Nanoconfinement: An Electrochemical Perspective.

Most relevant systems of interest to modern chemists rarely consist of a single phase. Real-world problems that require a rigorous understanding of chemical reactivity in multiple phases include the development of wearable and implantable biosensors, efficient fuel cells, single cell metabolic characterization techniques, and solar energy conversion devices. Within all of these systems, confinement effects at the nanoscale influence the chemical reaction coordinate. Thus, a fundamental understanding of the nanoconfinement effects of chemistry in multiphase environments is paramount. Electrochemistry is inherently a multiphase measurement tool reporting on a charged species traversing a phase boundary. Over the past 50 years, electrochemistry has witnessed astounding growth. Subpicoampere current measurements are routine, as is the study of single molecules and nanoparticles. This Perspective focuses on three nanoelectrochemical techniques to study multiphase chemistry under nanoconfinement: stochastic collision electrochemistry, single nanodroplet electrochemistry, and nanopore electrochemistry.

CuBO2 : A Potential Alternative for NiO as a Hole Acceptor Layer.

P-type metal oxides, and in particular NiO, are typically used as hole accepting layers in dye-sensitized photocathodes. Delafossites (CuMO2 ) with M=B, Al, Cr or Ga have recently been proposed as attractive substitutes for NiO, with theoretically a higher hole mobility than NiO, therefore allowing a higher efficiency when the photocathode is applied in solar to fuel devices. We have experimentally validated the photoelectrochemical performance of photocathodes consisting of nanoporous CuBO2 (CBO) on Fluorine-doped Tin Oxide substrates, photosensitized with a light absorbing P1 dye. Femtosecond transient absorption and time-resolved photoluminescence studies show that light-induced hole injection occurs from the P1 dye into the CBO in a few ps, comparable to the time constant observed for NiO-based photocathodes. Importantly, the CBO-based photocathode shows significantly slower charge recombination than the NiO-based analogue. These results illustrate the promise of CBO as a p-type semiconductor in solar energy conversion devices.

Enhanced Heat Flow between Charged Nanoparticles and an Aqueous Electrolyte.

Heat transfer through the interface between a metallic nanoparticle and an electrolyte solution has great importance in a number of applications, ranging from nanoparticle-based cancer treatments to nanofluids and solar energy conversion devices. However, the impact of the surface charge and dissolved ions on heat transfer has been scarcely explored so far. In this study, we compute the interface thermal conductance between hydrophilic and hydrophobic charged gold nanoparticles immersed in an electrolyte using equilibrium molecular dynamics simulations. Compared with an uncharged nanoparticle, we report a 3-fold increase of the Kapitza conductance for a nanoparticle surface charge of +320 mC/m2. This enhancement is shown to be approximately independent of the surface wettability, charge spatial distribution, and salt concentration. This allows us to express the Kapitza conductance enhancement in terms of the surface charge density on a master curve. Finally, we interpret the increase of the Kapitza conductance as a combined result of the shift of the water density distribution toward the charged nanoparticle and an accumulation of the counterions around the nanoparticle surface which increase the Coulombic interaction between the liquid and the charged nanoparticle. These considerations help us to apprehend the role of ions in heat transfer close to electrified surfaces.

A numerical and experimental study on a novel micro heat pipe PV/T system

The photovoltaic/thermal (PV/T) module, as an efficient solar energy conversion device, has gained significant interest worldwide. Particularly, the novel PV/T with micro heat pipe (MHP-PV/T) exhibits favorable performances in cold regions, especially when the ambient temperature drops below 0 °C. This study focuses on the application of MHP-PV/T in Lanzhou, a city located in northwest China. During the typical winter season, the net average electrical efficiency and thermal efficiency can reach 12.8% and 26.4%, respectively. A two-dimensional mathematical model of MHP-PV/T was developed and validated with experimental results. The simulation results aligned well with the experiment data. Furthermore, it was observed that increasing the width and number of MHPs can lead to further improvements in the electrical efficiency and the thermal efficiency. Lastly, regression equations were established, and dimensionless processing was performed to correlate solar radiation intensity with electrical efficiency, thermal efficiency and total efficiency in Lanzhou.

Metal-Organic Framework Glass Catalysts from Melting Glass-Forming Cobalt-Based Zeolitic Imidazolate Framework for Boosting Photoelectrochemical Water Oxidation.

Sluggish oxygen evolution kinetics and serious charge recombination restrict the development of photoelectrochemical (PEC) water splitting. The advancement of novel metal-organic frameworks (MOFs) catalysts bears practical significance for improving PEC water splitting performance. Herein, a MOF glass catalyst through melting glass-forming cobalt-based zeolitic imidazolate framework (Co-agZIF-62) was introduced on various metal oxide (MO: Fe2O3, WO3 and BiVO4) semiconductor substrates coupled with NiO hole transport layer, constructing the integrated Co-agZIF-62/NiO/MO photoanodes. Owing to the excellent conductivity, stability and open active sites of MOF glass, Co-agZIF-62/NiO/MO photoanodes exhibit a significantly enhanced photoelectrochemical water oxidation activity and stability in comparison to pristine MO photoanodes. From experimental analyses and density functional theory calculations, Co-agZIF-62 can effectively promote charge transfer and separation, improve carrier mobility, accelerate the kinetics of oxygen evolution reaction (OER), and thus improve PEC performance. This MOF glass not only serves as an excellent OER cocatalyst on tunable photoelectrodes, but also enables promising opportunities for PEC devices for solar energy conversion.

Metal‐Organic Framework Glass Catalysts from Melting Glass‐Forming Cobalt‐Based Zeolitic Imidazolate Framework for Boosting Photoelectrochemical Water Oxidation

AbstractSluggish oxygen evolution kinetics and serious charge recombination restrict the development of photoelectrochemical (PEC) water splitting. The advancement of novel metal–organic frameworks (MOFs) catalysts bears practical significance for improving PEC water splitting performance. Herein, a MOF glass catalyst through melting glass‐forming cobalt‐based zeolitic imidazolate framework (Co‐agZIF‐62) was introduced on various metal oxide (MO: Fe2O3, WO3 and BiVO4) semiconductor substrates coupled with NiO hole transport layer, constructing the integrated Co‐agZIF‐62/NiO/MO photoanodes. Owing to the excellent conductivity, stability and open active sites of MOF glass, Co‐agZIF‐62/NiO/MO photoanodes exhibit a significantly enhanced photoelectrochemical water oxidation activity and stability in comparison to pristine MO photoanodes. From experimental analyses and density functional theory calculations, Co‐agZIF‐62 can effectively promote charge transfer and separation, improve carrier mobility, accelerate the kinetics of oxygen evolution reaction (OER), and thus improve PEC performance. This MOF glass not only serves as an excellent OER cocatalyst on tunable photoelectrodes, but also enables promising opportunities for PEC devices for solar energy conversion.

Quantum-sized TiO2 particles as highly stable super-hydrophilic and self-cleaning antisoiling coating for photovoltaic application

Soiling influences power generation and reduces the power conversion efficiency of solar energy conversion devices. In this regard, we successfully synthesized highly photocatalytic active quantum-size TiO2 particles with an average particle size of 6 nm and utilized the same to develop a highly transparent antisoiling coating. The material is characterized by small angle X-ray scattering, and the average particle size is found to be 6 nm. Automated spray coating technique was employed for the development of antisoiling coating on PV cover glass and minimodule. The coating exhibited exceptional weather stability (IEC 61646) for over 1500 h, excellent photoinduced superhydrophilicity in a span of 60 mins. Photocatalytic activity of the antisoiling coating is studied by analyzing the degradation of methylene blue and 4-chlorophenol. Promising antisoiling performance was observed from the antisoiling coated PV module as it resulted in 2.5% lower soiling loss compared to that of not-coated minimodules. The coatings exhibited excellent mechanical stability and Omni transparency.

Rational Control of Near-Infrared Colloidal Thick-Shell Eco-Friendly Quantum Dots for Solar Energy Conversion.

Thick-shell colloidal quantum dots (QDs) are promising building blocks for solar technologies due to their size/composition/shape-tunable properties. However, most well-performed thick-shell QDs suffer from frequent use of toxic metal elements including Pb and Cd, and inadequate light absorption in the visible and near-infrared (NIR) region due to the wide bandgap of the shell. In this work, eco-friendly AgInSe2 /AgInS2 core/shell QDs, which are optically active in the NIR region and are suitable candidates to fabricate devices for solar energy conversion, are developed. Direct synthesis suffers from simultaneously controlling the reactivity of multiple precursors, instead, a template-assisted cation exchange method is used. By modulating the monolayer growth of template QDs, gradient AgInSeS shell layers are incorporated into AgInSe2 /AgInS2 QDs. The resulting AgInSe2 /AgInSeS/AgInS2 exhibits better charge transfer than AgInSe2 /AgInS2 due to their favorable electronic band alignment, as predicted by first-principle calculations and confirmed by transient fluorescence spectroscopy. The photoelectrochemical cells fabricated with AgInSe2 /AgInSeS/AgInS2 QDs present ≈1.5-fold higher current density and better stability compared to AgInSe2 /AgInS2 . The findings define a promising approach toward multinary QDs and pave the way for engineering the QDs' electronic band structures for solar-energy conversion.

Solar Energy Conversion and Electron Storage by a Cu2O/CuO Photocapacitive Electrode

Solar conversion devices are generally connected with energy storage systems to overcome the influence of sunlight variability. Developing an integrated solar energy conversion and storage device is an attractive approach to compensate for the energy loss of directly connecting these separate devices. In this work, a photocapacitive device is developed based on the Cu2O/CuO heterostructure, with Cu2O as a light absorber and CuO providing a platform for electron and ion storage. The coupling of Cu2O and CuO leads to a high specific capacitance of 135 mF/cm2 under bias and an open-circuit potential of 0.62 VRHE. A photo-charge and dark-discharge ability of Cu2O/CuO system under zero-bias is also discovered and explained based on the concept of Faradaic junction. This work presents an avenue for the investigation of high-performance Cu2O-based solar energy storage devices.