Photoelectrochemical Solar Cells Research Articles

Optimization and comparative evaluation of optoelectronic properties of hydrothermally synthesized CdIn2Te4 thin films: PEC performance

Herein, hydrothermal route was directly employed to synthesize Indium doped CdTe nanocrystalline thin films. The influence of In doping on the optical, structural, morphological and photoelectrochemical solar cell properties have been investigated. The optical absorption study illustrates that, maximum absorption was observed in between 500–700 nm with decrease in band gap energy from 1.47 to 1.35 eV as function of In doping. Structural analysis reveals that, transition in crystal structure from hexagonal to tetragonal on In doping in CdTe. Morphological analysis demonstrates that, evolution of 1-D nanowire like morphology in CdIn2Te4 thin film. Compositional analysis confirms the presence of Cd, In and Te elements in CdIn2Te4 thin film with stoichiometric atomic percentage. X-ray photoelectron spectroscopy (XPS) analysis confirms that, presence of Cd, In and Te ions in its valence states of Cd2+, In3+ and Te2− respectively. Current density-voltage measurement illustrates that, CdIn2Te4 photocathode shows improved PEC performance with photoconversion efficiency 2.84%. The improved photovoltaic performance of In doped CdTe photocathode was explained in detail with the help of Nyquist plots and corresponding circuit model of the electron impedance spectra.

Unsymmetrically pyrazole-3-carboxylic acid substituted phthalocyanine-based photoanodes for use in water splitting photoelectrochemical and dye-sensitized solar cells

A new photosensitizer, PCA-ZnPc-2, was synthesized through the asymmetric functionalization of phthalocyanine ring with a pyrazole-3-carboxylic acid as the electron-withdrawing and anchoring group and six hexylsulfanyl as the bulky electron-donating groups. PCA-ZnPc-2 was tested in dye-sensitized solar cells (DSSCs) and its performance was compared with PCA-ZnPc-1. It was found that PCA-ZnPc-2 has higher electron-donating ability which is favorable for light harvesting and suppress the dye aggregation on TiO2 when compared to PCA-ZnPc-1. Also, the new photosensitizer was used in dye-sensitized photoelectrochemical cells for hydrogen production under visible irradiation. The results show that PCA-ZnPc-2 is a promising photosensitizer to harvest the red/near-IR regions.

Photoelectrochemical performance of spray-deposited Fe-doped ZnS0.2Se0.8 thin films

Binary and ternary II–VI group semiconductor compounds are materials with potential use in various optoelectronic applications, including photoelectrochemical (PEC) solar cells. Thin films of ZnS0.2Se0.8 with various Fe-doping concentrations were successfully deposited on fluorine-doped tin oxide-coated glass substrates at a deposition temperature of 275 °C using the chemical spray pyrolysis. PEC cells with Fe:ZnS0.2Se0.8 thin film/1 M polysulphide/C (graphite) configurations were designed, and the effect of Fe doping on the PEC performance was studied. The results showed that Fe doping in ZnS0.2Se0.8 enhanced the performance of the PEC cells significantly. The optimum concentration was 0.20 mol%. The flat band potential and junction barrier height were maximum at this concentration, with values of −1.18 V and 0.27 eV, respectively. The junction ideality factors of the 0.20 mol% Fe-doped ZnS0.2Se0.8 thin film-based PEC cell in the dark and under illumination were found to be 1.21 and 1.17, respectively. The photovoltaic power output characteristics were boosted by Fe doping with a concentration of 0.20 mol%, with the open circuit voltage being 320 mV and the short circuit current being 1.48 mA cm−2. The solar-to-electrical conversion and the fill factor of the 0.20 mol% Fe-doped ZnS0.2Se0.8 thin film-based PEC cells were superior, with values of 2.84% and 0.60, respectively. A PEC cell with a 0.20 mol% Fe-doped ZnS0.2Se0.8 photosensitive thin film had the highest spectral sensitivity, at a wavelength of 375 nm, with an optical band gap of 3.30 eV.

Investigation of Strain Effects on Photoelectrochemical Performance of Flexible ZnO Electrodes

In this report, the growth of zinc oxide (ZnO) nanocrystals with various morphologies, nanoflower, nanosheet, and nanorod, on flexible stainless steel (SS) foils to be utilized as photoanodes in photoelectrochemical (PEC) solar cells has been presented. It has been aimed to provide flexibility and adaptability for the next generation systems with the incorporation of SS foils as electrode into PEC cells. Therefore, physical deformation tests have been applied to the prepared ZnO thin film photoanodes. These thin films have been thoroughly characterized before and after straining for better understanding the relationship between the morphology, straining effect and photoelectrochemical efficiency. We observed a notable increase in the maximum incident photon-to-current efficiency (IPCE) and durability of all ZnO photoelectrodes after straining process. The increase in IPCE values by 1.5 and 2.5 folds at 370 nm has been observed for nanoflower and nanorod morphologies, respectively after being strained. The maximum IPCE of 69% has been calculated for the ZnO nanorod structures after straining. Bending of the SS electrodes resulted in the more oriented nanorod arrays compared to its flat counterpart, which improved both the light absorption and also the photo-conversion efficiency drastically. The finite-difference time-domain simulations have also been carried out to examine the optical properties of flat and bent ZnO electrodes. Finally, it has been concluded that SS photoanodes bearing ZnO semiconducting material with nanoflower and nanorod morphologies are very promising candidates for the solar hydrogen generator systems in terms of efficiency, durability, flexibility, and lightness in weight.

Solvent dispersible nanocomposite based on Reduced Graphene Oxide and in-situ decorated gold nanoparticles

A facile in situ colloidal approach is reported to synthesize a novel hybrid nanocomposite formed of 3,4-dimethylbenzenethiol (DMBT)-capped Au NPs, decorating flakes of 1-pyrene-carboxylic acid (PCA) functionalized Reduced Graphene Oxide (RGO). In the nanocomposite, the Au NPs and RGO sheets are anchored by means of the aromatic PCA linker and the DMBT capping ligand, both ensuring electronic coupling due to particle/RGO and interparticle π-π interactions, respectively. The short aromatic thiol has been selected to i. yield additional binding sites for the NPs to the PCA-RGO surface, ii. potentially enhance electron conductivity and promote charge transfers, and iii. enable dispersibility in organic solvents.The role of the synthetic parameters on the resulting Au NPs morphology and on their organization onto the PCA-RGO sheets has been comprehensively investigated in order to elucidate the mechanism underlying the in situ NPs formation. Organic dispersions of the PCA-RGO flakes, densely and uniformly decorated with a multilayer network of DMBT-coated Au NPs, 2–3 nm in size, have been achieved, thus overcoming limitations previously reported for similar hybrid materials. The prepared nanostructures are attractive functional platforms for future FETs and (photo)electrochemical (bio)sensors, (photo)catalysis, photodetectors, memory devices and solar cells.

(Invited) Tailoring Metal Nanostructures for Energy-Efficient Electroreduction of CO2 and O2

Electrocatalysts play a vital role in the development of renewable energy technologies based on electrical-chemical energy conversions, such as fuel cells, electrolyzers, photoelectrochemical solar cells and metal-air batteries. Many metallic nanostructures have emerged as promising candidates for such electrocatalytic applications, but the performances are yet to be improved to meet the technical and cost-effectiveness standards for practical implementations. On the other hand, it traditionally relies on the model-catalyst studies of well-defined extended surfaces for mechanistic understanding of electrocatalysis, but discrepancies in catalytic performance and knowledge gaps are also realized to be present between the extended surfaces and nanomaterials. The latter is probably not only due to the intrinsically different bulk and surface structures of materials at these two extremes of size, but also caused by the challenges in probing the active sites and reaction pathways on nanostructured materials. This presentation aims to discuss two examples of our efforts on tailoring metallic nanostructures for electrocatalytic applications: i) highly dense Cu nanowires for the electroreduction of CO2 and CO, and ii) Co/Pt core/shell nanoparticles as sustainable electrocatalysts for the oxygen reduction reaction (ORR). These nanostructures are characterized by combining electron-based microscopic imaging, diffraction and elemental mapping, while the surface structures are probed by using surface-specific adsorption/desorption of small molecules (e.g., COad and OHad). The gained structural information is correlated to the measured catalytic activity, durability and/or selectivity, based on which computational simulations are further performed to understand the established structure-property relationships, depict the active sites and reveal the catalytic enhancement mechanisms. Our work highlights the great potential of tailoring nanostructured materials to improve the energy conversion and chemical transformation efficiencies of electrochemical systems.

Efficient Ultrathin Liquid Junction Photovoltaics Based on Transition Metal Dichalcogenides.

Ultrathin photovoltaics made of MoS2 or WSe2 have the potential to convert solar energy to electricity with high efficiency because all photogenerated carriers are produced at a charge-collecting interface. However, solid-state monolayer photovoltaic devices typically require that charge carriers travel parallel to, instead of perpendicular to, the three atom-thick material toward charge-collecting contacts. Parallel charge transport across long distances decreases energy conversion efficiency. Here we demonstrate proof-of-concept monolayer and bilayer TMD|I-,I3-|Pt photoelectrochemical solar cells that use a conformal liquid electrolyte junction for efficient perpendicular charge transport over significantly larger active areas than solid state systems. Efficient perpendicular charge transport is evidenced by high peak internal quantum efficiencies (IQE) of 44.2, 9.1, and 10.5% for 0.4 mm2 MoS2, WSe2, and MoS2/WSe2 domains in a predominantly monolayer MoS2/WSe2 film. The monochromatic energy conversion efficiencies are competitive with state-of-the-art solid-state monolayer heterojunction photovoltaics. However, inefficient light absorption limits the overall power conversion efficiency to 0.19% for this planar geometry monolayer photovoltaic system. Interestingly, correlated Raman and scanning photoelectrochemical microscopy measurements revealed a nonlinear scaling relation between IQE and layer thickness for MoS2, WSe2, and MoS2/MoS2/WSe2 domains within the heterojunction film. Specifically, the monochromatic energy conversion efficiency of bilayer MoS2 is an order of magnitude greater than monolayer MoS2 and MoS2/MoS2/WSe2and itexceeds MoS2/WSe2 by a factor of 4. The structure/function relationships are hidden in ensemble-level photoelectrochemical measurements. Although nanostructured or plasmonic electrode architectures are still needed to enhance overall light absorption, our study shows that the liquid junction approach represents a simple and rapid strategy to screen ultrathin TMD materials combinations, tune interfacial energetics, and make conformal electrical contacts in photoelectrochemical energy conversion systems for electricity or solar fuels production.

Selenium Nanoparticle-decorated Silicon Nanowires with Enhanced Liquid-Junction Photoelectrochemical Solar Cell Performance

Selenium nanoparticles decorated silicon nanowires (Se NPs@Si NWs) electrode is applied as a photoanode in a liquid junction photoelectrochemical (PEC) solar cell for the first time. Upon illumination, the Se NPs anchored along the axial length of Si NWs allow fast hole extraction at the radial Se/Si junctions, due to the p-type conduction nature of Se NPs thus enhancing electron-hole separation, and simultaneously increase the population of photoexcited electrons in Si NWs through light scattering that amplifies the effective light absorption of Si NWs. These attributes of Se NPs result in a power conver-sion efficiency (PCE) of 7.03% for the Se NPs@Si NWs based liquid junction solar cell encompassing a Br-/Br2 electrolyte and a carbon fabric counter electrode. This PCE is greater by 43% than that of the analogous Si NWs based cell. Se NPs are photo-conducting due to facile hole-propagation that occurs particularly along the c-axis of trigonal Se NPs with a hexago-nal crystal structure, and size effects improve the optical path length, factors that lead to a significantly improved perfor-mance. Compared to Pt or Au NPs that have been explored previously in combination with Si NWs, where their roles are distinctively different, Se NPs here, are not only more cost effective, and easy to synthesize on a large-scale, but they enable an improvement in PCE of Si NWs, by relying on unique mechanisms. Optical-, structural-, PEC-, and impedance- studies furnish a deep understanding of the phenomena involved in yielding a superior performing liquid junction PEC solar cell based on the Se NPs@Si NWs photoanode.

Nanoheterojunction through PbS nanoparticles anchored CdS nanowires towards solar cell application

Through simple chemical route, nanoheterojunction has been developed between CdS-nanowires (NWs) as core with PbS nanoparticles as a shell for photoelectrochemical solar cell application. The use of simple, cost effective and industry scalable chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) approaches for the deposition of CdS NWs and PbS nanoparticles, respectively has the added advantage. Well-tuned nano particle size of PbS through number of SILAR cycles over wide band gap CdS resulted into optical red shift which maximize the absorption region of solar spectrum responsible for yielding enhancement in light conversion efficiency than bare CdS. Device configured solar cell yields 15 fold enhancement in the power conversion efficiency in liquid configuration due to the well aligned nanoheterojunction between CdS and PbS analysed through photoelectron X-ray spectroscopy. This enhancement in efficiency has been correlated through flat band potential, electron life time, rate of recombination and external quantum efficiency.

Multinary CdZnIn2(SeTe)5 thin films produced by arrested precipitation technique for photoelectrochemical solar cells

Chemically synthesized multinary CdZnIn2(SeTe)5 thin film used as photoanodes in solar cell have been systematically investigated. The indium ion concentration dependent morphological evolution and its consequent effect on photoelectrochemical properties were studied. The growth mechanism for the morphological evolution of CdZnIn2(SeTe)5 thin films has been proposed. Optical absorption values varied with the indium concentration and the band gap energy is found in the range 1.87eV to 1.72 eV. The X-ray diffraction (XRD) patterns reveal the formation of rhombohedra, cubic and hexagonal CdZnIn2(SeTe)5 thin films with the preferred (110), (138) and (220) orientation for CdZnIn2(SeTe)5 microflower, which is further supported by the analysis of the high resolution transmission electron micrographs (HRTEM). The SEM image revealed that the surface morphology of multinary thin films have been changed to microflower by systematic control of indium ion concentration. Finally, current-voltage measurements at different concentration for solar cell with maximum efficiency were carried out in order to find out the dominant transport mechanisms. The solar cell fabricated shows the best conversion efficiency of 1.28%. The deposition of a certain amount of indium was beneficial to the improvement of photoelectrochemical conversion efficiency. To the best of our knowledge, it is the highest efficiency for CdZnIn2(SeTe)5 based photoanode solar cells fabricated from APT.

Implementation of Gyrinops Versteegii Gaharu Leaves as a Dye-Sensitized Solar Cell

Dye-Sensitized Solar Cell (DSSC) is a photoelectrochemical solarcell that uses electrolytes as the cargo transport medium. Gratzeldeveloped it as an alternative resource through the discovery of thelatest solar cell material by mimicking the photosynthesis processcalled photo-electrochemical reactions. According to the researchof Saputra, flavonoids can be used as dyes in Dye-Sensitized SolarCells, while Yanti in 2014 studied the agarwood leaf extract thatcontained flavonoids and chlorophyll. This study aimed to design,build, and test Dye-Sensitized Solar Cell by testing the lightabsorption, and the Performance of Dye-Sensitized Solar Cell usingAgarwood Chlorophyll. This research extracted the Gyrinopsversteegii that was grouped into young, medium and old leaves.With the same dose of extract, 15 grams of agarwood leaves weredissolved in 96% ethanol for 100 ml. The results showed that eventhough the maximum absorption power was the same, or 4.00, themedium leaves absorbed the light more than its wavelength range.The DSSC performance test results obtained the voltages of theyoung, medium, and old agarwood leaves that were 0.398 V, 0.399V, and 0.369 V. The currents of those leaves were 0.01 mA, 0.01mA, and 0.01 mA respectively.

The Effect of Trap States on the Optoelectronic Properties of Nanoporous Nickel Oxide

Nickel oxide (NiO) is often used as a hole-transporter material in both photovoltaic and photoelectrochemical solar cells. As a result of the reversible nickel(II)/(III) transformation, it is also electrochromic. These potential-dependent optoelectronic properties of this intriguing material, however, are yet to be fully understood. In this article, we show that the picture is more complicated than the generally discussed nickel(II)/(III) transformation, because of the presence of trap states. We reveal that the density of states is directly influenced by the applied potential in nanoporous NiO films; and show how it manifests in the electrical properties and Raman spectral features. We demonstrated that the population/depopulation of shallow trap states has an important role in dictating these changes. The presented insights can also contribute to the better understanding of the optoelectronic properties of different semiconductor electrodes under charging conditions.

Progress on Nanomaterials for Photoelectrochemical Solar Cells: from Titania to Perovskites

Solar cells have been the queen of alternative renewable energy for the earth. From silicon-based solar cells to the new generation of perovskite-based solar cells, the choice and performance of the materials of the corresponding cells are still the focus of research interest. Amongst, photoelectrochemical (PEC) solar cells trigger the use and exploration of nanomaterials to boost their cell’s performance. This short review focus on the development of nanomaterials used for PEC, from nanoparticles to the one-dimensional titanium dioxide (titania) such as nanofibers and nanotubes, as well as the hybrid system with the perovskite halide. The search for light-harvesting materials is also included especially natural dyes. The review ends with a strategy to marry the natural dyes' potential with the sophisticated structure of nanomaterials to result in an efficient natural dyes PEC solar cells.

A dual-function photoelectrochemical solar cell which assimilates light-harvesting, charge-transport and photoelectrochromic nanomaterials in a tandem design

This is the first known integration of a novel QD-sensitized photocathode with an electrochromic photoanode in a solar cell.

Iron Doped CdSe Films with Improved Photosensitivity and Stability for Use in a Liquid Junction Solar Cell

In the present investigation, transition metal Fe has been introduced in low levels in the CdSe matrix to formulate CdFeSe films for application in photoelectrochemical solar cells. Periodic voltammetry was employed to deposit the ternary films on FTO glass. Spectral characteristics, morphology, and composition of the matrices were determined by the respective physiochemical methods. The band gap energies of CdFeSe thin films were increased with the increase of Fe content. Electrochemical impedance spectroscopy, chronoamperometry, and photosensitivity of the film matrices were studied. In order to derive the functional parameters at the anode–electrolyte interface, the cell configuration, FTO/CdFeSe/S2––Sx2–/Pt, coupled with calomel reference electrode was used. Anodic stripping voltammetry was employed to investigate the inherent stability of the film matrices. The performance screening of the films ultimately indicates the best output in terms of photoconversion efficiency (η, %), fill factor (FF, %), a...

Colloidal synthesis of CuInS2 nanoparticles: Crystal phase design and thin film fabrication for photoelectrochemical solar cells

This study reports the colloidal synthesis of copper indium disulfide (CuInS2) nanoparticles in different crystal phases to be employed as thin film photoanodes in photoelectrochemical water splitting process. First, CuInS2 nanoparticles with chalcopyrite-, zincblende-, wurtzite-as well as polytypic-phases have been synthesized using hot injection method. The effects of solvent, temperature and type of precursors on the phase design have been thoroughly investigated via various spectroscopic techniques such as XRD, SEM, HRTEM, UV-Vis and PL spectroscopy and Zeta particle size analysis. The XRD spectra have been revealed that the all the targeted nanoparticles had good crystallinity and free from undesired binary sulfides. The synthesized nanoparticles have been re-dispersed in N, N-dimethylformamide (DMF) to form nanoink paste and applied on fluorine doped tin oxide coated glass substrate by doctor blade technique. DMF has been found to be an enviable solvent for thin film fabrication since it could lead to the crack free and uniform surface formation. The chalcopyrite thin film has shown the best photoelectrochemical performance with the photocurrent density of ∼15 mA cm−2 and conversion efficiency of 6.7%. Howbeit, thin films photoanodes bearing wurtzite, zincblende and polytypic CuInS2 nanoparticles have been investigated to compare the performance of different crystal phases for photoelectrochemical solar cell applications. Moreover, it should be emphasized that all thin film electrodes have been investigated under 1-sun condition without any surface modification, chemical treatment and etching. Additionally, the thin films except wurtzite structure exhibited good stability along 2 h under dark and illuminated conditions.

Properties of spray deposited ZnSxSe1−x thin films for photoelectrochemical solar cell application

The wide band gap II–VI group materials have been extensively studied for optoelectronic applications. The polycrystalline zinc sulphoselenide (ZnSxSe1−x) thin films have been spray deposited onto FTO coated glass substrates at temperature of 275 °C. PEC cells were formed with n-ZnSxSe1−x thin films/1 M (NaOH + Na2S + S)/C configuration to study various photoelectrochemical properties. The study signifies n-type conductivity of ZnSxSe1−x thin films. Significant photoelectrochemical response has been witnessed for the films deposited with x = 0.2 composition. The flat band potential of − 1.09 V has been observed for ZnS0.2Se0.8 thin film. The junction ideality factors in dark and under radiance are found to be 1.37 and 1.32 respectively. ZnS0.2Se0.8 thin films produces 268 mV open circuit voltage and 816 µA cm−2 short circuit current subsequent to efficiency and fill factor of 1.27% and 0.58 respectively. Spectral response characteristics display a sharp peak at 425 nm for x = 0.2, resulting in a band gap of 2.92 eV. These results imply that change in composition ‘x’ has substantial effect on the photovoltaic properties.

Decoration of 3D ZnO nanoelectrodes with CuInS2 for solar water splitting

This study reports the decoration of zinc oxide (ZnO) nanosheets with copper indium sulfide (CuInS2) via sequential metal deposition and post sulfurization methods for photoelectrochemical solar cell application. The three dimensional (3D) ZnO nanosheets are hydrothermally grown on conductive glass substrates by chemical bath deposition. Then, copper/indium metallic alloy is deposited via magnetron sputtering and annealed at high temperature in the presence of elemental sulfur to form CuInS2 absorber on the surface of 3D nanosheets. Photoelectrochemical measurements indicate that the decoration of CuInS2 layer over the ZnO nanosheets results in significant increase in the photocurrent density to 28 mA cm−2 (at 0.5 V vs Ag/AgCl) leading a remarkable amount of hydrogen generation during solar water splitting process, 1387 μmol measured at 0 V vs Ag/AgCl under 1 sun-illumination for 4 h.

Hybrid photoelectrochemical and photovoltaic cells for simultaneous production of chemical fuels and electrical power.

Harnessing solar energy to drive photoelectrochemical reactions is widely studied for sustainable fuel production and versatile energy storage over different timescales. However, the majority of solar photoelectrochemical cells cannot drive the overall photosynthesis reactions without the assistance of an external power source. A device for simultaneous and direct production of renewable fuels and electrical power from sunlight is now proposed. This hybrid photoelectrochemical and photovoltaic device allows tunable control over the branching ratio between two high-value products of solar energy conversion, requires relatively simple modification to existing photovoltaic technologies, and circumvents the photocurrent mismatches that lead to significant loss in tandem photoelectrochemical systems comprising chemically stable photoelectrodes. Our proof-of-concept device is based on a transition metal oxide photoanode monolithically integrated onto silicon that possesses both front- and backside photovoltaic junctions. This integrated assembly drives spontaneous overall water splitting with no external power source, while also producing electricity near the maximum power point of the backside photovoltaic junction. The concept that photogenerated charge carriers can be controllably directed to produce electricity and chemical fuel provides an opportunity to significantly increase the energy return on energy invested in solar fuels systems and can be adapted to a variety of architectures assembled from different materials.

Improved Photovoltaic Performances of Quasi-Solid Photoelectrochemical Solar Cells By Mitigating Charge Recombination Rate at Electrolyte and Photoanode Interface

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as high energy conversion efficiency and low production cost etc. Recently, cobalt complexes have been suggested as one of the most promising candidates for replacing conventional iodine redox couples owing to their high voltage characteristics. Even though respectable energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of DSSCs. In this work, therefore, novel polymer gel electrolytes (PGEs) including cobalt complexes as redox couples have been prepared for efficient and long-term stable DSSCs. In addition, several ways to mitigate the charge recombination rate at the interface between PGE and photoanode have been systematically investigated. The electron transport properties in mesoporous TiO2 electrodes (i.e. electron lifetime and diffusion coefficients) have been evaluated through IMPS and IMVS analyses. In addition, the photovoltaic performances of DSSCs employing prepared PGEs have been evaluated via the J-V curve measurements and various electrochemical characterizations. Acknowledgments: This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).