Incident Photon-to-current Conversion Efficiency Value Research Articles

Structural, spectroscopic and improved photoelectrochemical properties of TiO2/C composites with anatase/brookite matrix, prepared by air-thermolysis of microspherical titanium glycolate

X-ray powder diffraction, Raman spectroscopy, HRTEM, electron diffraction and differential thermal analysis methods were used to study structural and spectroscopic properties and thermal stability of the products obtained by air-thermolysis of Ti-glycolate in the temperature range 300–450°С. TiO2/C composites were obtained, which have anatase/brookite matrix with a variable degree of crystallinity and contain different contents of brookite and free polymeric-like carbon with COO− groups. It was found that the residual content of carbonaceous component and the intensity of exothermal decomposition of Ti-glycolate have an effect on the formation of brookite-rich TiO2 matrix. Correlations between the phase composition and the free carbon content suggest that during crystallization brookite/carbon nanoparticles are more stable than anatase/carbon nanoparticles. PEC tests demonstrated that the composite photoanode, which has the greatest degree of crystallinity, the optimal carbon content and is most enriched with brookite, exhibits the greatest incident photon-to-current conversion efficiency (IPCE), and its IPCE peak value is twice as great as the IPCE peak value for Degussa P25. The increased IPCE value is associated with the preferable formation of carbon/brookite/anatase heterostructures. The carbon component has an optical gap of approx. 1.1 eV, and at the optimal contents it ensures efficient photogeneration and transfer of electrons into the conduction band of brookite and then into the conduction band of anatase. HRTEM study demonstrated the formation of such heterostructure with anatase/brookite heterojunction.

CuFeO2/Cu Photoelectrode Modified with SrTiO3 Perovskite for Efficient Hydrogen Generation from Sanitation Water

We prepared a perovskite material, copper-doped strontium titanate (Cu-SrTiO3), using the chemical bath deposition method and cast it on a CuFeO2/Cu photoelectrode to generate hydrogen from sanitation water splitting. This preparation method considers a simple mass product and does not depend on complex techniques. The prepared perovskite materials had a compact nano-/microstructure. Both CuFeO2 and Cu-SrTiO3/CuFeO2 exhibited excellent optical properties, with bandgap values of 1.4 and 1.26 eV, respectively. Here, the prepared CuFeO2 and Cu-SrTiO3 thin films are used as photoelectrodes for hydrogen generation, and their current-voltage relationship is analyzed under various conditions, such as different light intensities, wavelengths, and temperatures. This approach is promising for using wastewater as a source of hydrogen gas without requiring any additional electrolyte, making it a dual-purpose approach for both hydrogen generation and wastewater treatment. Through the electrochemical study, increasing the light intensity from 25 to 100 mW.cm-2 resulted in a corresponding increase in the produced J ph values from -1.02 to -1.292 mA.cm-2. Similarly, the J ph values increased from -1.25 to -1.91 mA.cm-2 as the temperature increased from 30 to 70°C. We also calculated all thermodynamic parameters, the quantum efficiency (QE), and incident photon to current conversion efficiency (IPCE). For the Cu-SrTiO3/CuFeO2/Cu photoelectrode, the activation energy ( E a ) value was 14.14 kJ mol-1, while the Δ H ∗ and Δ S ∗ values were 11.46 kJ·mol-1 and 34.9 kJ-1·mol-1, respectively. Additionally, the IPCE value was 3.31%. The prepared photoelectrode showed high stability and low cost, making it a potential candidate for industrial applications.

Fabrication of Hematite Photoanode Consisting of (110)-Oriented Single Crystals.

In this work, α-Fe2 O3 photoanode consisted of (110)-oriented α-Fe2 O3 single crystals were synthesized by a facile hydrothermal method. By using particular additive (C4 MimBF4 ) and regulation of hydrothermal reaction time, the Fe-25 consisted of a single-layer of highly crystalline (110)-oriented crystals with fewer grain boundaries, which was vertically grown on the substrate. As a result, the charge separation efficiency and photoelectrochemical (PEC) performance of Fe-25A (Fe-25 after dehydration treatment) have been greatly improved. Fe-25A yields a photocurrent of 1.34 mA cm-2 (1.23 V vs RHE) and an incident photon-to-current conversion efficiency (IPCE) of 31.95 % (380 nm). With the assistance of cobalt-phosphate water oxidation catalyst (Co-Pi), the PEC performance could be further improved by enhancing the holes transfer at electrode/electrolyte interface and inhibiting surface recombination. Fe-25A/Co-Pi yields a photocurrent of 2.67 mA cm-2 (1.23 V vs RHE) and IPCE value of 50.8 % (380 nm), which is 3.67 times and 2.39 times as that of Fe-2A/Co-Pi. Our work provides a simple method to fabricate highly efficient Fe2 O3 photoanodes consist of characteristic (110)-oriented single crystals with high crystallinity and high quality interface contact to enhance charge separation efficiencies.

The fingerprint of charge transport mechanisms on the incident photon-to-current conversion efficiency spectra of perovskite solar cells

Perovskite solar cells (PSCs), the most promising nanostructured solar cells for large-scale production, have been fabricated with different types of electron and hole collectors to improve efficiency and stability. Incident photon-to-current conversion efficiency (IPCE) is an important measurement to evaluate the optical/electrical behavior of the structure to modify the device structure. In this research, we have investigated how different mechanisms affect the IPCE spectra and the difference between short-circuit current density (Jsc) recorded from the current density-voltage (J-V) and the IPCE curves of n-i-p PSCs. Results show that by removing the electron-transport layer (ETL) in a device with a compact PSK layer, the IPCE spectrum does not change and only a slight shift of interference peak position is observable. By removing the hole-transport layer (HTL), not only IPCE value drops substantially for all wavelengths, its shape (including interference peaks) deforms significantly in the 500–800 nm wavelength range. In the case of cells with imperfect HTLs, only a slight change in this range (not the blue range) is observable. Utilizing different charge-transport and PSK materials, we have shown how significant the nonlinearity of the device's characteristics (such as charge-transfer resistance) with light intensity increases in the difference between Jsc value from J-V and integrated Jsc from IPCE curves. Selecting charge-collecting layers also directly affect interference peaks in IPCE spectra, for instance using TiO2 nanograss as ETL or CuIn0.75Ga0.25S2/carbon hole-collector instead of Spiro OMeTAD/Au hole-collector results in disappearing interference peaks.

Superior incident photon-to-current conversion efficiency of Mo-doped activated carbon supported CdS-sensitized solar cells.

In this study, the performance of activated carbon (AC) produced from defatted black cumin (Nigella sativa L.) by chemical activation with zinc chloride (ZnCl2) activator in photovoltaic application is evaluated. It is of great importance to increase the photovoltaic efficiency of cadmium sulfide (CdS)-based solar cells, which are widely used in photovoltaic applications, with AC support. The main purpose of the study is to determine how the incident photon-to-current conversion efficiency (IPCE) of undoped and Mo-doped AC supported CdS semiconductor materials changes in the presence of AC support material and to interpret the observed effect in the light of literature. For these reasons, in the study, AC supported CdS (CdS/AC) (5%, 10%, and 15% by weight) and Mo-doped CdS/AC semiconductor materials with different molybdenum (Mo) concentrations (0.33%, 1%, 3%) are produced by chemical precipitation method. Produced CdS/AC and Mo-doped CdS/AC semiconductor materials are characterized by IPCE, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) measurements. Based on the result values, the optimum CdS concentration with the highest IPCE (%) value is determined as 10% (for CdS/AC). As a result of the experimental measurements, the optimum Mo concentration with the maximum IPCE (%) value is found as 1% (for Mo-doped CdS/AC). In particular, it is clear that an appreciable increase (from 4.70 to 39.00%) in IPCE (%) of 1% Mo-doped 10% CdS/AC semiconductor material is achieved when compared to pure CdS. Thus, the ability to increase the photovoltaic efficiency of CdS-based solar cells, which are widely used in photovoltaic applications, with AC support has been clearly demonstrated. This study presents a new strategy to increase the solar cell efficiency of semiconductor-based solar cell structures using biowaste-based AC supported CdS semiconductor materials.

Increased visible light absorption and charge separation in 2D–3D In2S3-ZnO heterojunctions for enhanced photoelectrochemical water splitting

A 2D–3D (ZnO/In2S3 heterojunction) photoanodes have been grown via a two-step physical vapor deposition (PVD) technique for ZnO, followed by chemical vapor deposition (CVD) for In2S3 2D nanolayers to study the photoelectrochemical (PEC) properties in the present study. 2D nanolayers of In2S3 deposited on ZnO thin film provide increased surface area and efficient electron-hole separation at the heterojunction interface which results in a significant reinforcement of photocurrent density and incident photon-to-current conversion efficiency (IPCE). The ZnO/In2S3 heterojunction shows a photocurrent density of 2.4 mAcm−2 at 1.23 V vs. RHE and IPCE value of 43% at 0.5 V with the stability of more than 100 min in comparison to both pristine ZnO and In2S3 samples. Measurements of photocurrent density at different wavelengths for the heterojunction sample confirm that the enhancement in photoelectrical response at the interface is due to higher absorption in the visible range as compared to pristine ZnO thin films and increased carrier separation at the interface in comparison to the pristine 2D In2S3 nanolayers. The experimental determination of the work function (KPFM), valence band offset (XPS), and bandgap values (absorption spectra) confirm favorable type II band alignment resulting in efficient charge transfer within the heterojunction sample. The present approach can be extended to other 2D heterojunction systems having unique optical and electronic properties.

Electric polarization tune enhanced photoelectrochemical performance of visible light active ferroelectric Bi0.5Na0.5TiO3 nanostructure photoanode

Significantly enhanced photoelectrochemical (PEC) performance of the visible light active photoanodes of ferroelectric Bi0.5Na0.5TiO3 nanostructure has been demonstrated by tuning the electrical polarization of the film. The photocurrent density of unpoled Bi0.5Na0.5TiO3 photoanode increases from 0.48 mA cm−2 at 1 V with respect to Ag/AgCl to 1.21 mA cm−2 after negative poling, whereas it decreases to 0.18 mA cm−2 after positive poling. The incident photon-to-current conversion efficiency (IPCE) of the nanostructure photoanodes has been observed to vary from 5% to 28% just by changing the direction of electric polarization. The change in the PEC performance and enhancement in the IPCE value after switching the polarization state of Bi0.5Na0.5TiO3 photoanodes have been attributed to the modification in the band bending at the interface of semiconductor electrode/electrolyte, leading to facilitate the increment in photogenerated charge transfer efficiency. The modulation in the band bending and variation in the charge transfer method after switching the polarization state are confirmed by Mott-Schottky (M-S) and electrochemical impedance spectroscopy (EIS) measurements. Our work provides a new visible light active ferroelectric nanostructure material for efficient visible light active photoelectrochemical performance.

Biotemplated Synthesis of Titanium Oxide Nanoparticles in the Presence of Root Extract of Kniphofia schemperi and Its Application for Dye Sensitized Solar Cells

Metal oxide nanoparticles prepared by biological route using green plant parts as a template are eco-friendly as well as yield good results than the conventional methods. This present study focusses on biosynthesis and characterization of TiO2 NPs using root extract of Kniphofia schemperi for dye-sensitized solar cells. TiO2 NPs were synthesized using 0.25 M titanium tetra butoxide in the presence of root extract of Kniphofia schemperi with the volume ratios. The analysis result revealed that the synthesized TiO2 NPs were thermally stable above 500°C and have spherical morphology, with the average crystalline size of 11.7, 8.3, and 8.6 nm, and band gap energy of 3.35 eV, 3.33 eV, and 3.36 eV, respectively, for the TiO2 NPs prepared at the volume ratios of 2 : 3, 1 : 1, and 3 : 2. Biosynthesized TiO2 NPs were used as photoanode in dye-sensitized solar cells (a device used for converting absorbed light into electricity). Solar cell devices were fabricated using roots of Kniphofia schemperi sensitizer in the presence of TiO2 NPs biosynthesized within (2 : 3, 1 : 1, and 3 : 2) volume ratio, which showed power conversion efficiency of 0.039%, 0.117%, and 1.3%. Incident photon to current conversion efficiency (IPCE) analysis using TiO2 (2 : 3, 1 : 1, and 3 : 2) photoelectrodes showed 6.64%, 2.66%, and 18%. Among the biosynthesized TiO2 different volume ratios, TiO2 (3 : 2) NPs showed relatively maximum solar cell efficiency and IPCE value due to its uniform spherical shape that enables to absorb large dye molecules on its surface, and this intern improves device efficiency.

Effect of cyclodextrin cavity size on the photovoltaic performance of unanchored ruthenium(II) polypyridine complex-containing dye-sensitized solar cells

We report the effect of cyclodextrin (CD) cavity size on the photovoltaic performance of dye-sensitized solar cells (DSSCs) containing inclusion complexes of tris(2,2′-bipyridyl)ruthenium(II) ([Ru(bpy)3]2 + ) in various CDs ([Ru(bpy)3]2 + / CD). The incident photon-to-current conversion efficiency (IPCE) of the [Ru(bpy)3]2 + -containing DSSC at 460 nm was calculated to be 8.1%, and this value was enhanced by the formation of [Ru(bpy)3]2 + / CD. The IPCE values of [Ru(bpy)3]2 + / α-CD-containing, [Ru(bpy)3]2 + / β-CD-containing, and [Ru(bpy)3]2 + / γ-CD-containing DSSCs were 8.8%, 8.9%, and 11.2%, respectively. It was concluded that the difference of IPCE values of [Ru(bpy)3]2 + / CD-containing DSSCs were caused by the CD cavity size, which affected the host–guest interaction between [Ru(bpy)3]2 + and the CD. These findings indicated that the cavity size of γ-CD is suitable to promote the photovoltaic conversion of DSSCs containing an unanchored photosensitizing dye with nonplanar molecular structure such as ruthenium(II) polypyridine and diimine copper(I) complexes.

Influence of Poly(Vinylidene fluoride) on photovoltaic performance of interfacially engineered band gap modulated P3TAA-co-P3HT perovskite solar cell at ambient condition

Recently, mixing of foreign polymers with perovskite increases light absorption yielding a large increase of power conversion efficiency (PCE) and also increasing longevity of perovskite solar cells (PSCs). The previous studies are limited at dry or at very low humid conditions. Here, for practical use, we report a new series of poly(vinylidene fluoride) (PVDF)-perovskite (MAPbI3) hybrid solar cells made from different PVDF concentrations e.g. 0.0, 0.25, 0.5, 1.0, 2.5, 5.0 mg/ml, and are designated as H1, H2, H3, H4, H5, and H6, respectively. The average grain size, measured from SEM images of MAPbI3 (312 ± 91 nm) has decreased with increasing PVDF concentration showing a minimum (215 ± 43 nm) for H5 sample. UV–Vis absorption spectra show the highest absorption for H5 sample for all the wavelengths. The intensities and width of X-ray diffraction peaks increase in the hybrids (H3 and H5) from pristine perovskite indicating increase of crystallinity and crystalline size. We have used an interfacially engineered, band gap modulated poly(3-thiophene acetic acid)–co-poly(3-hexyl thiohene) P3TTA - co - P3HT, with 43 mol% P3TAA content as hole transporting material (HTM) and TiO2 as electron transporting material (ETM) to fabricate the cell. The PCE, measured on illumination with a light of one sun at ambient condition (humidity 75–85%, temperature 30 °C), is 12% for H5 PSC, highest reported so far, and it is 20% higher from pristine PSC. The incident photon to current conversion efficiency (IPCE) data exhibit strong absorption in the broad range 300–800 nm showing a maximum IPCE value of 84%. Impedance spectral data indicate that lifetime of photo-generated charges are highest (48.4 m s) explaining the highest PCE value for H5-PSC compared to other hybrids. The longevity of the H5-PSC is significantly (54%) higher than PSC made with pristine perovskite measured and stored under identical ambient condition.

Ce-doped CdS quantum dot sensitized TiO2 nanorod films with enhanced visible-light photoelectrochemical properties

Ce-doped CdS quantum dot (QD) sensitized TiO2 nanorods films on FTO substrates are for the first time prepared by a combination of hydrothermal and successive ionic layer adsorption and reaction (SILAR) method. The physicochemical properties of as-prepared samples are examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible spectrometry (UV–vis). The as-prepared Ce-CdS QD sensitized TiO2 nanorods photoelectrodes is applied into photoelectrochemical (PEC) cells to investigate their PEC properties, including the photocurrent density and incident photon-to-current conversion efficiency (IPCE), which exhibit a maximum 1.4-time enhancement in photocurrent density and 1.6-time enhancement in IPCE value, compared with undoped photoelectrode. Furthermore, a maximum 1.4-time higher formic acid yields was obtained in a versatile photoanode-driven PEC CO2 reduction system. The results of electrochemical analysis show that the Ce-CdS QDs/TiO2 photoelectrodes exhibit an increased visible light absorbance, a higher carrier density, a longer electron lifetime and more effective separation of photogenerated electron-hole pairs. This is most probably due to the existence of Ce 4f electronic states in the mid-gap region of Ce-CdS QDs, which is confirmed by a simple theoretical calculation and a redox couple Ce3+/Ce4+ accelerating the photogenerated holes migration. The study demonstrates that the variable valency Ce-doping may be a promising approach to achieve high photoelectric conversion efficiency for chalcogenides semiconductors.

Push–Pull Distyryl Boron Dipyrromethenes as Near‐Infrared Sensitizers for Dye‐Sensitized Solar Cells

AbstractA diiodo distyryl boron dipyrromethene (BODIPY) with an ethyl ester group at the meso position was prepared. This compound underwent palladium‐catalyzed Sonogashira cross‐coupling reactions with 4‐(diphenylamino)phenylethyne and 4‐(dimethylamino)phenylethyne to give the corresponding dialkynyl derivatives. After alkaline hydrolysis and acidic work‐up, all three compounds were converted to the carboxyl analogues, which could bind to the surface of TiO2 for application in dye‐sensitized solar cells (DSSCs). These compounds, in particular the dialkynyl analogues, possessed a push–pull structure and a highly conjugated π system, which shifted the Q band to the near‐infrared region. Electrochemical studies revealed that they had appropriate HOMO and LUMO levels for the construction of DSSCs comprising a TiO2 electrode and an electrolyte containing an I3−/I− redox couple. The optimized structures, frontier molecular orbitals, and absorption spectra of these sensitizers were calculated using density functional theory. The diiodo distyryl BODIPY‐based DSSC showed a photovoltaic conversion efficiency of 2.78 % under AM 1.5G standard sunlight and a maximum incident photon‐to‐current conversion efficiency (IPCE) of >45 % at 780 nm. The DSSCs fabricated with the dialkynyl distyryl BODIPYs could achieve an IPCE value of approximately 20 % at 840 nm and a broader photoresponse over the whole visible range extending up to approximately 950 nm in the near‐infrared region.

Role of S, N co-doped graphene quantum dots as a green photosensitizer with Ag-doped ZnO nanorods for improved electrochemical solar energy conversion

Photoelectrochemical (PEC) properties of Ag doped ZnO nanorods (Ag-ZnO NRs) have been studied in details. Ag-ZnO NRs photoanodes demonstrated superior photoconversion efficiency (i.e. photon to hydrogen), photoresponse properties, incident-photon-to-current conversion efficiency (IPCE), compared to pristine ZnO nanorods. S and N co-doped graphene quantum dots (S,N-GQDs) were synthesized by hydrothermal process and utilized as a green photosensitizer for further improvement of photoelectrochemical activities. S,N-GQD sensitized nanorods showed photoconversion efficiency (η) ∼1.1%, and short circuit photocurrent (JSC) ∼0.96mA/cm2, which are 3.4 times and 2.7 times higher than ZnO NRs. Sensitization with S,N-GQDs also improved the IPCE value and attained maximum 62.8% at 350nm, which is 2.2 times higher compared to ZnO NRs.

High-performance BiVO4 photoanodes cocatalyzed with an ultrathin α-Fe2O3 layer for photoelectrochemical application

A high-performance bismuth vanadate (BiVO4) photoanode cocatalyzed with an ultrathin α-Fe2O3 layer was fabricated for photoelectrochemical water splitting and organic pollutant degradation. The ultrathin α-Fe2O3 layer, which can faciliate the holes transfer to the surface efficiently and thus avoid high charge recombination, was deposited on the surface of the BiVO4 photoanode using a spin-coating-based successive ionic layer adsorption and reaction (SILAR) method. The Fe2O3/BiVO4 photoanode was characterized by various techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy, while its photoelectrochemical activity was investigated by linear sweep voltammetry and incident photon-to-current conversion efficiency (IPCE). The optimized Fe2O3/BiVO4 photoanode demonstrated a photocurrent density of 1.63mAcm−2 at 1.23V vs. a reversible hydrogen electrode (RHE) in a 0.1M KH2PO4 (pH 7) electrolyte under simulated AM1.5G solar light and an IPCE value above 27% at 400nm, which were 2.14 times and triple that of pristine BiVO4 photoanode, respectively. Furthermore, the Fe2O3/BiVO4 photoanode showed excellent stability and efficiency for the photoelectrocatalytic degradation of phenol compared with the bare BiVO4 photoanode. The chemical oxygen demand (COD) removal ratio increased from 42.3% to 68.89% after 120min, which could be attributed to the efficient separation and transfer of the photogenerated carriers.

Fabrication of a dye-sensitized solar cell containing a noncarboxylated spiropyran-derived photomerocyanine with cyclodextrin

Abstract The fabrication, photovoltaic conversion, and photo-response of dye-sensitized solar cell (DSSC) containing a noncarboxylated spiropyran 1,3,3-trimethylindolino-β-naphthopyrylospiran ( 1 ) and carboxymethyl-β-cyclodextrin sodium salt (CM-β-CD) were investigated for the first time. In fact, we found the adsorption of photomerocyanine form (PMC) of 1 and inclusion complexes between the PMC and CM-β-CD (PMC/CM-β-CD) to the TiO 2 surface. The formation of PMC/CM-β-CD was confirmed by fluorescence spectroscopy. The incident photon-to-current conversion efficiency (IPCE) of the PMC-containing DSSC obtained 4.1% under 570-nm light irradiation, and the highest IPCE reached 11.1% by inclusion effect of CM-β-CD. Similar, the fillfactor and the open-circuit voltage were improved by CM-β-CD layer. The IPCE value of PMC/CM-β-CD-containing DSSC was decreased by visible light treatment, and it was considered that decrease of IPCE values are attributed to the formation of PMC isomer. Therefore, we demonstrated the photovoltaic conversion and photoresponsivity of the DSSC by incorporating a noncarboxylated PMC with inclusion effect of CM-β-CD layer.

Nanoporous carbon/WO3 anodes for an enhanced water photooxidation

This work provides new insights in the field of applied photoelectro chemistry based on the use of nanoporous carbons as additives to tungsten oxide for the photooxidation of water under potential bias. Using a nanoporous carbon of low surface functionalization as additive to WO3 we have shown the dependence of the photochemical oxidation of water with the wavelength of the irradiation source. Photoelectrochemical responses obtained under monochromatic illumination show a significant increase in the incident photon-to-current conversion efficiency (IPCE) values for electrodes featuring up to 20 wt% carbon additive. Photoelectrochemical transient responses also show a sharp potential dependence, suggesting that the performance of the electrodes is strongly influenced by the carrier mobility and recombination losses. Despite the modest IPCE values of the W/NC electrodes (due to high bulk recombination and poor electron transport properties of the electrodes), our data shows that the incorporation of an optimal amount of nanoporous carbon additive to WO3 can enhance the carrier mobility of the semiconductor, without promoting additional recombination pathways or shadowing of the photoactive oxide.

Influence of wide band gap oxide substrates on the photoelectrochemical properties and structural disorder of CdS nanoparticles grown by the successive ionic layer adsorption and reaction (SILAR) method.

The photoelectrochemical properties of nanoheterostructures based on the wide band gap oxide substrates (ZnO, TiO2, In2O3) and CdS nanoparticles deposited by the successive ionic layer adsorption and reaction (SILAR) method have been studied as a function of the CdS deposition cycle number (N). The incident photon-to-current conversion efficiency (IPCE) passes through a maximum with the increase of N, which is ascribed to the competition between the increase in optical absorption and photocarrier recombination. The maximal IPCE values for the In2O3/CdS and ZnO/CdS heterostructures are attained at N ≈ 20, whereas for TiO2/CdS, the appropriate N value is an order of magnitude higher. The photocurrent and Raman spectroscopy studies of CdS nanoparticles revealed the occurrence of the quantum confinement effect, demonstrating the most rapid weakening with the increase of N in ZnO/CdS heterostructures. The structural disorder of CdS nanoparticles was characterized by the Urbach energy (EU), spectral width of the CdS longitudinal optical (LO) phonon band and the relative intensity of the surface optical (SO) phonon band in the Raman spectra. Maximal values of EU (100–120 meV) correspond to СdS nanoparticles on a In2O3 surface, correlating with the fact that the CdS LO band spectral width and intensity ratio for the CdS SO and LO bands are maximal for In2O3/CdS films. A notable variation in the degree of disorder of CdS nanoparticles is observed only in the initial stages of CdS growth (several tens of deposition cycles), indicating the preservation of the nanocrystalline state of CdS over a wide range of SILAR cycles.

Effects of number and position of meta and para carboxyphenyl groups of zinc porphyrins in dye-sensitized solar cells: structure-performance relationship.

Porphyrin sensitizers containing meta- and para-carboxyphenyl groups in their meso positions have been synthesized and investigated for their performance in dye-sensitized solar cells (DSSCs). The superior performance of para-derivative compared to meta-derivative porphyrins was revealed by optical spectroscopy, electrochemical property measurements, density functional theory (DFT) calculations, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, incident photon-to-current conversion efficiency (IPCE), electrochemical impedance spectroscopy (EIS), and stability performance. Absorption spectra of para-carboxyphenyl-substituted porphyrins on TiO2 show a broader Soret band compared to meta-carboxyphenyl-substituted porphyrins. ATR-FTIR spectra of the studied porphyrins on TiO2 were applied to investigate the number and mode of carboxyl groups attached to TiO2. The VOC, JSC, and IPCE values of para-series porphyrins were distinctly superior to those of meta-series porphyrins. The Nyquist plots of the studied porphyrins show that charge injection in para-series porphyrins is superior to that in meta-series porphyrins. The orthogonally positioned para derivatives have more efficient charge injection and charge transfer over charge recombination, whereas the efficiencies of flat-oriented meta derivatives are retarded by rapid charge recombination. Photovoltaic measurements of the studied meta- and para-carboxyphenyl-functionalized porphyrins show that the number and position of carboxyphenyl groups play a crucial role in the performance of the DSSC. Our results indicate that para-carboxyphenyl derivatives outperform meta-carboxyphenyl derivatives to give better device performance. This study will serve as a guideline for the design and development of organic, porphyrin, and ruthenium dyes in DSSCs.

Enhancing photoelectrochemical performance with a bilayer-structured film consisting of graphene–WO3nanocrystals and WO3vertically plate-like arrays as photoanodes

A bilayer-structured film photoelectrode, containing an under-layer of reduced graphene oxide–WO3 nanocrystals (G-WNC) or WO3 nanocrystals (WNC) and a top layer of WO3 vertically plate-like arrays (WP), was designed and fabricated by solution-based and hydrothermal methods. The morphologies, structural and optical properties of as-prepared composites were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet visible (UV-Vis) spectrometry. Moreover, the photoelectrochemical properties were studied through linear scan voltammetry, electrochemical impedance spectroscopy (EIS) and incident photon to current conversion efficiency (IPCE). It was found that the photocurrents of WP, WNC/WP and G-WNC/WP films were 0.68, 0.80 and 1.23 mA cm−2 at 1.2 V (vs. Ag/AgCl) under AM 1.5G illumination, respectively, whereas the IPCE values were 28.12%, 31.33% and 39.52% successively at the wavelength of 355 nm. EIS data illustrated that the charge transfer resistance was clearly reduced by introducing graphene in the underlayer of the composite film. The enhancement of G-WNC/WP film could be ascribed to the synergic effects of the bilayer structure and the limitation of charge recombination.

On the Substantially Improved Photoelectrochemical Properties of Nanoporous WO3 Through Surface Decoration with RuO2

Solar fuel generation, either through photochemical or photoelectrochemical (PEC) routes, is one of the most prominent pathways to harvest sunlight in order to contribute to a diversified and sustainable energy supply. Oxygen evolution reaction (OER) from aqueous solutions is the half reaction of different energy related reaction schemes, most importantly stoichiometric water splitting (H2 generation) or CO2 reduction. In this paper, we present PEC water oxidation (OER) on nanoporous WO3 films, decorated with RuO2 nanoparticles. The morphology and the composition of these nanostructured assemblies were characterized by high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry while their photo-electrochemical behavior was evaluated by photovoltammetry and incident photon-to-current conversion efficiency (IPCE) measurements. The O2 evolution capability was directly assessed by determining the amount of evolved O2 gas during PEC oxidation of water. The RuO2 electrocatalyst substantially increased photoanodic current flow through facile transfer of photogenerated holes from WO3 to the solution, thereby improving interfacial charge transfer kinetics. Both absolute and relative enhancement of photocurrents was analyzed as a function of the applied external bias potential giving important insight into the mechanistic details. Furthermore, the decisive roles of the amount of RuO2 co-catalyst and thermal pretreatment were established by synthesizing hybrid assemblies with different RuO2 coverage, and applying subsequent thermal treatment, respectively. Through careful optimization of the composition of the hybrid material, the IPCE value doubled at lower bias potentials and was increased close to the theoretical 100 % limit at higher positive potential values. These results demonstrate the synergy gained by combining the excellent photoanodic properties of nanoporous WO3 with the robust O2 evolution capabilities of RuO2.