Reduced Surface Recombination Research Articles

Tethering Cobalt Ions to BiVO4 Surface via Robust Organic Bifunctional Linker for Efficient Photoelectrochemical Water Splitting.

In the quest for efficient and stable oxygen evolution catalysts (OECs) for photoelectrochemical water splitting, the surface modification of BiVO4 is a crucial step. In this study, a novel and robust OEC, based on 3-(bis(pyridin-2-ylmethyl) amino) propanoic acid bifunctional linker known as dipicolyl alanine acid (DPAA) and cobalt ions, is prepared and fully characterized. The DPAA is anchored to the surface of BiVO4 and utilized to tether cobalt ions. The Co-DPAA/BiVO4 photoanode exhibits remarkable stability and efficiency toward photoelectrochemical water oxidation. Specifically, it showed anodic photocurrent increase of 7.1, 5.0, 3.0, and 1.3-fold at 1.23VRHE as compared to pristine BiVO4, DPAA/BiVO4, Co-BiVO4, and Co-Pi/BiVO4 photoanodes, respectively. The photoelectrochemical and IMPS studies revealed that the Co-DPAA/BiVO4 photoanode exhibits a longer transient decay time for surface-trapped holes, higher charge transfer kinetics, and charge separation efficiency compared to Co-Pi/BiVO4 and pristine BiVO4 photoelectrodes. This indicates that the Co-DPAA effectively reduces surface recombination and facilitates charge transfer. Moreover, at 1.23VRHE, the Co-DPAA/BiVO4 photoanode achieved a faradic efficiency of 92% for oxygen evolution reaction and could retain a turnover frequency of 3.65s-1. The- exhibited effeciency is higher than most of the efficient molecular oxygen evolution catalyst based on Ru.

Passivating perovskite surface defects via bidentate chelation for high-performing solar cells

Surface defects seriously damage carrier transport by forming non-radiative recombination centers on the perovskite film, which negatively affect the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Here we present a strong chelate coordination bond to anchor the surface of the perovskite film. Employing Bathophenanthroline (BPhen) as a π-conjugated bidentate chelator, the uncoordinated Pb2+ can be firmly anchored accompanying with the reduced surface recombination sites, giving rise to suppressed non-radiative recombination and enhanced charge carrier extraction. With the BPhen, the perovskite film shows an approximately threefold longer carrier lifetime than the control device, leading to a champion PCE of 24.09 % and a high stable performance with retained over 80 % of its initial efficiency after 1000 h exposed to relative humidity (RH) of 65 ± 5 %.

Preparation and Electrical Performance Analysis of a GaAs‐Based Tritium Battery

A nuclear battery is a promising candidate for small power supply sources in the military and commercial fields, but its output power and energy conversion efficiency need to be improved. This paper mainly describes a design, preparation, and electrical performance analysis of a GaAs-based tritium battery. The design of the tritium battery uses a multistage process with Monte Carlo and Matlab simulations. A titanium tritide source was prepared by a high-temperature tritium absorption device, and a GaAs semiconductor transducer was developed using a metal-organic chemical vapor deposition method. The D/Ti ratio and T/Ti ratio of the deuterium/tritium titanium films were 1.9 and 1.7, respectively. Two kinds of GaAs-based PIN junction semiconductor transducers were proposed and irradiated with the prepared tritium source. Their electrical properties were measured in situ and analyzed qualitatively. Under the irradiation of a 0.61-Ci tritium source, the short-circuit current of the device was 0.3 to 0.38 μA, the open-circuit voltage was 35 to 63 mV, the peak power was 2.8 to 6.4 nW, and the energy conversion efficiency of the GaAs semiconductor transducer was about 1.86%. It was found that an air gap between the GaAs semiconductor transducer and the radioactive source caused serious loss of beta particle energy, resulting in low output power and low energy conversion efficiency of the nuclear battery. The open-circuit voltage of the devices with a SiO2 passivation layer on the surface decreased both in a dark environment and in light illumination, but SiO2 passivation did not reduce surface recombination as expected. The research work in this paper will provide some valuable reference for the preparation and performance optimization of nuclear batteries.

4F-Phenethylammonium chloride as a key component for interfacial engineering of wide-bandgap perovskite absorber

The development of high-efficiency and stabilized tandem solar cells and solar cells for indoor light harvesting relies heavily on the fabrication of wide-bandgap (WBG) perovskite solar cells (PSCs) that exhibit exceptional efficiency and stability. In this study, we introduce an effective method for enhancing the optoelectronic properties of a 1.74 eV WBG perovskite absorber by interfacial engineering. Specifically, we utilize 4F-Phenethylammonium Chloride (4F-PEACL) as a key component for the surface treatment of perovskite layer. The treatment of perovskite with 4F-PEACL alters the surface stoichiometry, promoting self-doping and surface passivation, reducing surface recombination, and improving the optoelectronic properties of perovskite. Consequently, PCSs with perovskite treated with 4F-PEACL exhibit a notable power conversion efficiency of 20.27 %. Furthermore, the devices subjected to 4F-PEACL treatment demonstrate enhanced stability compared to the control devices across a range of testing settings. The findings of our study indicate that the utilization of organic salt perovskite passivation holds great potential in the development of efficient and stable WBG PSCs.

Insights into the role of Co3O4/Ti3C2 MXene hybrid material in photoelectrochemical water oxidation over BiVO4 photoanode

Developing efficient hole transport layers and water oxidation electrocatalysts is vital for improving the performance of photoelectrochemical (PEC) devices for water-splitting. In this work, we synthesized Co3O4 nanoparticles/Ti3C2-MXene hybrid material and utilized it as a dual-function material to transport the photogenerated holes and catalyze the water oxidation reaction. It was found that the modification of BiVO4 with Co3O4/Ti3C2-MXene prolonged the lifetime of the photogenerated holes by 13.7-fold (i.e. from 0.26 s for BiVO4 to 3.56 s for Co3O4/Ti3C2/BiVO4) and significantly reduced the charge transfer resistance. The modification of BiVO4 with only Ti3C2-MXene resulted in significant surface recombination more likely due to the high concentration of the accumulated holes in the Mxene layer because of its low electrocatalytic activity toward water oxidation reaction. Employing the Co3O4/Ti3C2-MXene hybrid material significantly reduced the rate constant of surface recombination and dramatically enhanced the charge transfer efficiency (i.e. from 0.17% for BiVO4 to 14.0% for Co3O4/Ti3C2/BiVO4 at 0.65 VRHE). Under optimized conditions, the Co3O4/Ti3C2/BiVO4 photoanode was able to deliver 5.05 mA cm−2 at 1.23 VRHE and outperforms Ti3C2/BiVO4 and Co3O4/BiVO4 photoanodes. Moreover, it showed high stability for over 50 hours and reached a Faradaic efficiency of 90%. An applied bias photo-to-current efficiency (ABPE) value of 1.71% at 0.62 VPt was obtained for the overall water splitting. This work provides a facile method to reduce surface recombination and enhance the stability and PEC efficiency of BiVO4 photoanodes via the modification with dual-function oxygen evolution catalyst/hole transport layer hybrid material.

Optical and electrical characterization of solar cell with nanowires mimicking antireflection coating layers considering axial and radial PN junctions

AbstractIt has been well documented that the usage of a textured cover layer reduces reflection from the air‐solar cell interface, which ultimately enhances the power conversion efficiency (PCE) of a solar cell. The most commonly used patterns, such as pyramids, micropillars, nanowires (NW), and nanoholes have been widely studied and optimized. Besides using such NWs to enhance light absorption, this work also additionally considers the concept of mimicking the antireflection coating of single or multiple layers in minimizing the reflectance and thus enhancing the total absorptance further. It is shown here that at least one order of magnitude shorter multilayer NW pattern of 268 nm total height can outperform a standard NW of 4270 nm height, which needs less material and can also be fabricated at a reduced cost. Furthermore, the proposed design with reduced height has a significantly lower surface‐to‐volume ratio, which also reduces surface recombination loss than the other textured surface patterns. The results presented in this work have been comprehensively analyzed by initially optimizing optical absorption and then completing the electrical simulations. The optimized design in conjunction with a back reflector offers an efficiency as high as 16.434%.

Enhanced performance of fiber-based perovskite solar cell achieved by multi-functional high polymer doping strategy

Toward the realization of efficient, durable, and sustainable fiber-based perovskite solar cells (fb-PSCs), a comprehensive optimization strategy focused on enhancing electron transport layer (ETL), perovskite (PVK) photovoltaic layer, and hole transport layer (HTL) is presented. A champion PCE of 10.66 % with 37.9 % relative enhancement over control has been achieved in the optimized fb-PSC. A significantly improved mechanical resilience and storage durability are also recorded. Decorating the SnO2 ETL with methylammonium lead triiodide (MAPbI3) strengthened the ETL/PVK interfacial integrity, and doping the MAPbI3 layer with the multi-functional polymer of PJ71 remarkably enhanced the PVK layer’s crystallization quality, and effectively passivated the grain boundary defects. A CO2 pre-treatment of the spiro-OMeTAD HTL enhanced its hole conductivity. It is the synergetic combination of these methodologies that mutually contributed to the performance boost of the fb-PSC. The phenomenological model based on layer conductance shows that the PVK layer chiefly influences the device’s anti-bending ability, followed by the ETL, and HTL the least impact. To further enhance the PCE of fb-PSCs, optimizing the interface and minimizing the stress-induced defects are essential. These measures, coupled with increasing carrier diffusion length and reducing surface recombination, are key to advancing the fb-PSC performance. An encapsulation with polyolefin elastomer substantially reduced the potential lead leakage of the device, and facilitated its eco-friendly application.

Reduced Surface Recombination in Extended-Perimeter LEDs toward Electroluminescent Cooling.

III-V semiconductor light-emitting diodes (LEDs) are a promising candidate for demonstrating electroluminescent cooling. However, exceptionally high internal quantum efficiency designs are paramount to achieving this goal. A significant loss mechanism preventing unity internal quantum efficiency in GaAs-based devices is nonradiative surface recombination at the perimeter sidewall. To address this issue, an unconventional LED design is presented, in which the distance from the central current injection area to the device's perimeter is extended while maintaining a constant front contact grid size. This approach effectively moves the perimeter beyond the lateral spread of current at an operating current density of 101-102 A/cm2. In p-i-n GaAs/InGaP double heterojunction LEDs fabricated with varying sizes and perimeter extensions, a 19% relative increase in external quantum efficiency is achieved by extending the perimeter-to-contact distance from 25 to 250 μm for a front contact grid size of 450 × 450 μm2. Utilizing an in-house developed Photon Dynamics model, the corresponding relative increase in internal quantum efficiency is estimated to be 5%. These results are ascribed to a significant reduction in perimeter recombination due to a lower perimeter-to-surface area (P/A) ratio. However, in contrast to lowering the P/A ratio by increasing the front contact grid size of LEDs, the present method enables these improvements without affecting the required maximum current density in the microscopic active LED area under the front contact grid. These findings aid in the advancement of electroluminescent cooling in LEDs and could prove useful in other dedicated semiconductor devices where perimeter recombination is limiting.

Organic indoor PV: vanishing surface recombination allows for robust device architecture.

As a promising candidate to drive low-power, off-grid applications, organic indoor photovoltaics are beginning to attract research and commercial attention. In organic photovoltaic devices, charge transport layers are often used to promote the extraction of majority carriers, while blocking minority carriers. They can however be a source of device degradation and introduce additional complexity to the fabrication of the device stack. Here, a simplified, yet performant indoor OPV architecture is demonstrated with extended absorber thickness and without electron transport layer (ETL). We show that the diminished impact of the ETL on indoor OPV results from a drastically reduced surface recombination in thick absorber devices. However, the ETL remains important under strong, outdoor illumination, since in that case the reduced surface recombination is overwhelmed by bulk recombination. The proposed simplified device architecture with thick absorber (>500 nm) has great potential in large-scale production of indoor OPV.

Numerical Simulation and Design of All-Thin-Film Homojunction Perovskite/c-Si Tandem Solar Cells

Double-junction solar devices featuring wide-bandgap and narrow-bandgap sub-cells are capable of boosting performance and efficiency compared to single-junction photovoltaic (PV) technologies. To achieve the best performance of a double-junction device, careful selection and optimization of each sub-cell is crucial. This work presents the investigation of an all-thin-film two-terminal (2T) monolithic homojunction perovskite (PVK)/c-Si tandem cell using Silvaco TCAD simulation. The front sub-cell utilizes homojunction PVK that has a bandgap of 1.72 eV, whereas the rear sub-cell uses thin c-Si with a bandgap of 1.12 eV. Both cells are connected via a p++/n++ silicon tunnel diode. Experimental calibration of the heterojunction PVK and c-Si cells yields power conversion efficiencies (PCE) of 18.106% and 17.416%, respectively. When integrated into an initial PVK/c-Si tandem, the resulting cell achieves a PCE of 29.38%. To compare the performance, the heterojunction PVK layer is replaced with an n-p homojunction PVK layer, revealing the impact of the absence of a surplus built-in electric field in the perovskite film as a strong limiting factor. Further, a thorough investigation of four distinct structures for the n-p homojunction PVK cell is conducted. The four structures include a complete cell, electron transport layer (ETL)-free, hole transport layer (HTL)-free, and carrier transport layer (CTL)-free structures. The results show that the CTL-free structure has significant potential after applying certain optimization techniques that result in reducing surface recombination, enhancing the built-in electric field, and improving light absorption. With the current-matching condition achieved, the tandem efficiency reaches 36.37%.

Modeling the performance of perovskite solar cells with inserting porous insulating alumina nanoplates

Peng et al. [Science 379 683 (2023)] reported an effective method to improve the performance of perovskite solar cells by using thicker porous insulator contact (PIC)-alumina nanoplates. This method overcomes the trade-off between the open-circuit voltage and the fill factor through two mechanisms: reduced surface recombination velocity and increased bulk recombination lifetime due to better perovskite crystallinity. From arguments of drift-diffusion simulations, we find that an increase in mobility and carrier recombination lifetime in bulk are the key factors for minimizing the resistance-effect from thicker PICs and achieving a maximum power conversion efficiency (PCE) at approximately 25% reduced contact area. Furthermore, the partially replacement of perovskite films with thicker PICs would result in a reduction in short-current density, but the relative low refractive index of the PICs imbedded into the high refractive index perovskite creates light trapping structures that compensate for this loss.

Excellent crystalline silicon surface passivation by transparent conductive Al-doped ZnO/ITO stack

The surface passivation materials commonly used in crystalline silicon (c-Si) solar cells are either electrically insulating or opaque to the solar spectrum, which poses the electrical loss or optical loss. Hence it is of great significance to explore functional films that are simultaneously transparent, conductive and passivating for c-Si. In this study, we successfully tune two most well-known transparent conductive oxides, i.e. Al-doped ZnO (AZO) and indium tin oxide (ITO), as excellent passivation layers for c-Si surface. The AZO film is grown by atomic layer deposition and is capped with a magnetron-sputtered ITO film. Dynamic secondary ion mass spectrometry reveals that such stack design can retain higher hydrogen concentration on c-Si surface than a single AZO film during annealing. In addition, the AZO should be highly doped to reduce the energy barrier height around c-Si surface, thereby increasing the charge carrier asymmetry and thus reducing surface recombination. It is also highly crucial to optimize the annealing temperature and interfacial silicon oxide. As such, the effective minority carrier lifetime reaches 2.0 ms and the implied open-circuit voltage approaches 700 mV. Besides, the AZO/ITO stacked films possess negligible optical absorption, low sheet resistance (∼90 Ω/sq), and outstanding antireflection effect on c-Si surface.

Fabricating and investigating a beveled mesa with a specific inclination angle to improve electrical and optical performances for GaN-based micro-light-emitting diodes.

In this Letter, beveled mesas for 30 × 30 µm2 GaN-based micro-light-emitting diodes (µLEDs) with different inclination angles are designed, fabricated, and measured. We find that µLED with a mesa inclination angle of 28° has the lowest internal quantum efficiency (IQE) and the highest injection current density at which the peak IQE is obtained. This is due to the increased quantum confined Stark effect (QCSE) at the mesa edge. The increased QCSE results from the strong electric field coupling effect. Instead of radiative recombination, more nonradiative recombination and leakage current will be generated in the sidewall regions. Besides, the smallest angle (28°) also produces the lowest light extraction efficiency (LEE), which arises from the optical loss caused by the sidewall reflection at the beveled surface sides. Therefore, the inclination angle for the beveled mesa has to be increased to 52° and 61° by using Ni and SiO2 as hard masks, respectively. Experimental and numerical results show that the external quantum efficiency (EQE) and the optical power can be enhanced for the fabricated devices. Meanwhile, the reduced surface recombination rate also decreases the leakage current.

Bulk In Situ Reconstruction of Heterojunction Perovskite Enabling Stable Solar Cells Over 24% Efficiency

AbstractHeterojunction perovskite solar cells combine the stability of 2D perovskites and the high efficiency of 3D perovskites, making them an excellent photovoltaic candidate. While heterojunctions with intermixed or gradient perovskites can reduce surface recombination, the aggregation and phase distribution of 2D perovskite induce transport losses, thereby limiting device fill factors. Accordingly, a bulk in situ reconstruction (BISR) strategy is proposed to induce the reconstruction of 3D perovskites on a minim self‐assembled 2D crystal seed, forming heterojunction perovskite that runs through the entire active layer. This facilitates charge extraction, relieves tensile stress, and avoids the decomposition of perovskite on grain boundaries. As a result, the best‐performing heterojunction perovskite solar cells show a high‐power conversion efficiency (PCE) of 24.06% with 82.9% FF for the small‐area device (0.105 cm2) and a superior PCE of 19.2% for the large‐area module (5 × 5 cm2). Importantly, the unencapsulated device shows dramatically improved operational stability, maintaining 87% of its initial efficiency after 8000 h of storage under ambient atmosphere at room temperature. This work provides an effective and simple approach to establish heterojunction perovskite to simultaneously boost the efficiency and stability of PSCs.

Electrochemical Growth and Structural Study of the AlxGa1−xAs Nanowhisker Layer on the GaAs Surface

This work presents a novel, cost-effective method for synthesizing AlxGa1−xAs nanowhiskers on a GaAs surface by electrochemical deposition. The process begins with structuring the GaAs surface by electrochemical etching, forming a branched nanowhisker system. Despite the close resemblance of the crystal lattices of AlAs, GaAs, and AlxGa1−xAs, our study highlights the formation of nanowhiskers instead of layer-by-layer film growth. X-ray diffraction analysis and photoluminescence spectrum evaluations confirm the synthesized structure’s crystallinity, uniformity, and bandgap characteristics. The unique morphology of the nanowhiskers offers promising implications for solar cell applications because of the increased light absorption potential and reduced surface recombination energy losses. We conclude by emphasizing the need for further studies on the growth mechanisms of AlxGa1−xAs nanowhiskers, adjustments of the “x” parameter during electrochemical deposition, and detailed light absorption properties of the formed compounds. This research contributes to the field of wideband materials, particularly for solar energy applications, highlighting the potential of electrochemical deposition as a flexible and economical fabrication method.

All-perovskite tandem solar cells with 3D/3D bilayer perovskite heterojunction.

All-perovskite tandem solar cells promise higher power-conversion efficiency (PCE) than single-junction perovskite solar cells (PSCs) while maintaining a low fabrication cost1-3. However, their performance is still largely constrained by the subpar performance of mixed lead-tin (Pb-Sn) narrow-bandgap (NBG) perovskite subcells, mainly because of a high trap density on the perovskite film surface4-6. Although heterojunctions with intermixed 2D/3D perovskites could reduce surface recombination, this common strategy induces transport losses and thereby limits device fill factors (FFs)7-9. Here we develop an immiscible 3D/3D bilayer perovskite heterojunction (PHJ) with type II band structure at the Pb-Sn perovskite-electron-transport layer (ETL) interface to suppress the interfacial non-radiative recombination and facilitate charge extraction. The bilayer PHJ is formed by depositing a layer of lead-halide wide-bandgap (WBG) perovskite on top of the mixed Pb-Sn NBG perovskite through a hybrid evaporation-solution-processing method. This heterostructure allows us to increase the PCE of Pb-Sn PSCs having a 1.2-µm-thick absorber to 23.8%, together with a high open-circuit voltage (Voc) of 0.873 V and a high FF of 82.6%. We thereby demonstrate a record-high PCE of 28.5% (certified 28.0%) in all-perovskite tandem solar cells. The encapsulated tandem devices retain more than 90% of their initial performance after 600 h of continuous operation under simulated one-sun illumination.

Effective interface treatment by zirconium acetylacetonate for inverted methylammonium-rich perovskite solar cells

Surface passivation of halide perovskites using suitable agents is crucial to enhance the performance of corresponding solar cells as surface defects dominate nonradiative recombination in the devices. Meantime, it is important to reduce surface recombination as well as improve the contact nature at the interface between perovskite and transport layers by introducing such an agent in devices. Many works have achieved remarkable results by designing novel interfacial modifiers, but it is still a challenge to realize excellent interface treatments by less-complicated small molecules. Here, we demonstrate that zirconium acetylacetonate (ZrAcac) provides both effective methylammonium-rich perovskites surface passivation and excellent interfacial charge transport channel between the perovskite and fullerene-based electron transport layer in inverted cell structure. We theoretically find that the deep in-gap states from the PbI and IPb anti-site defects are effectively eliminated by the strong interaction between ZrAcac and the perovskite surface, which is further confirmed by experimental Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Meantime, the suitable conduction band minimum and deep valance band maximum of the ZrAcac on perovskites surface made a better electron transporting channel and interfacial anti-transfer barrier. Consequently, the corresponding device without encapsulation shows a power conversion efficiency (PCE) of 22.1% and still retains 80% of its initial PCE after 400 h of exposure to a constant environment (∼10% RH and 30 °C). This work provides a simple and cheap alternative perovskite interface treatment for future large-scale commercialization of perovskite solar cells.

Photoelectrochemical Performance of Strontium Titanium Oxynitride Photo-Activated with Cobalt Phosphate Nanoparticles for Oxidation of Alkaline Water.

Photoelectrochemical (PEC) solar water splitting is favourable for transforming solar energy into sustainable hydrogen fuel using semiconductor electrodes. Perovskite-type oxynitrides are attractive photocatalysts for this application due to their visible light absorption features and stability. Herein, strontium titanium oxynitride (STON) containing anion vacancies of SrTi(O,N)3-δ was prepared via solid phase synthesis and assembled as a photoelectrode by electrophoretic deposition, and their morphological and optical properties and PEC performance for alkaline water oxidation are investigated. Further, cobalt-phosphate (CoPi)-based co-catalyst was photo-deposited over the surface of the STON electrode to boost the PEC efficiency. A photocurrent density of ~138 μA/cm at 1.25 V versus RHE was achieved for CoPi/STON electrodes in presence of a sulfite hole scavenger which is approximately a four-fold enhancement compared to the pristine electrode. The observed PEC enrichment is mainly due to the improved kinetics of oxygen evolution because of the CoPi co-catalyst and the reduced surface recombination of the photogenerated carriers. Moreover, the CoPi modification over perovskite-type oxynitrides provides a new dimension for developing efficient and highly stable photoanodes in solar-assisted water-splitting reactions.

Reducing nonradiative recombination in perovskite solar cells with a porous insulator contact.

Inserting an ultrathin low-conductivity interlayer between the absorber and transport layer has emerged as an important strategy for reducing surface recombination in the best perovskite solar cells. However, a challenge with this approach is a trade-off between the open-circuit voltage (Voc) and the fill factor (FF). Here, we overcame this challenge by introducing a thick (about 100 nanometers) insulator layer with random nanoscale openings. We performed drift-diffusion simulations for cells with this porous insulator contact (PIC) and realized it using a solution process by controlling the growth mode of alumina nanoplates. Leveraging a PIC with an approximately 25% reduced contact area, we achieved an efficiency of up to 25.5% (certified steady-state efficiency 24.7%) in p-i-n devices. The product of Voc × FF was 87.9% of the Shockley-Queisser limit. The surface recombination velocity at the p-type contact was reduced from 64.2 to 9.2 centimeters per second. The bulk recombination lifetime was increased from 1.2 to 6.0 microseconds because of improvements in the perovskite crystallinity. The improved wettability of the perovskite precursor solution allowed us to demonstrate a 23.3% efficient 1-square-centimeter p-i-n cell. We demonstrate here its broad applicability for different p-type contacts and perovskite compositions.

Carbon-Protected BiVO4—Cu2O Thin Film Tandem Cell for Solar Water Splitting Applications

Carbon-protected BiVO4 photoanode and Cu2O photocathode tandem photoelectrochemical (PEC) system has been explored to reduce surface recombination and enhance the stability of the photoelectrodes. In addition to the carbon layer, the electrodeposited FeOOH nanolayer and drop-casted MoS2 co-catalyst layer on the photoanode and photocathode, respectively improve the reaction kinetics. The optimized photoanode (Mo-BiVO4/C/FeOOH) and photocathode (Cu2O/C/MoS2) produces current densities of ~1.22 mA cm−2 at 1.23 V vs. RHE and ~−1.48 mA cm−2 at 0 V vs. RHE, respectively. The obtained photocurrent is higher than bare photoelectrodes without a carbon layer. Finally, a tandem cell has been constructed, and an unassisted current density of ~0.107 mA cm−2 is obtained for a carbon-protected BiVO4–Cu2O tandem PEC cell at zero bias. The improved stability and enhanced photocurrent of the carbon protective layer are attributed to its better charge transfer resistance and minimized surface defects. Carbon protective layer can be a viable option to improve the stability of photoelectrodes in aqueous media.