Incident Photon Conversion Efficiency Research Articles

Enhancement in solar hydrogen generation efficiency using InGaN photoelectrode after surface roughening treatment with nano-sized Ni mask

A significant enhancement in solar hydrogen generation efficiency has been achieved by inductive coupled etching (ICP) surface roughening treatment using nano-sized nickel mask. As much as 7 times improvement of photocurrent is demonstrated in comparison with a planar one fabricated from the same parent wafer. Under identical illumination conditions in HBr solution, the incident photon conversion efficiency (IPCE) shows an enhancement with a factor of 3, which even exceed 54% at 400 nm wavelength. We believe the enhancement is attributed to several facts including improvement in absorption, reacting area, carrier localization and carrier lifetime.

Activation of CdSe Quantum Dots after Exposure to Polysulfide

Polysulfide electrolyte is the most commonly utilized electrolyte in quantum dot-sensitized solar cells (QDSSCs). Recently, however, a redshift in the relative positions of the absorbance and incident photon conversion efficiencies of CdSe QDs in polysulfide solutions has been reported. We conduct extensive analyses of CdSe QD films comparing those exposed to polysulfide solution with unexposed films; indeed, a redshift in the absorbance is observed after exposure. Most strikingly, we observe that a photocurrent response from films immersed in sodium sulfite is observed only after exposure to polysulfide solution. We demonstrate this is due to a combination of both QD ripening and a change in the QD capping layer. The results demonstrate that a polysulfide processing step significantly alters the photoelectrochemical performance of QDs.

Plasmonic Cu(x)In(y)S2 quantum dots make better photovoltaics than their nonplasmonic counterparts.

A synthetic approach has recently been developed which results in Cu(x)In(y)S2 quantum dots (QDs) possessing localized surface plasmon resonance (LSPR) modes in the near-infrared (NIR) frequencies.1 In this study, we investigate the potential benefits of near-field plasmonic effects centered upon light absorbing nanoparticles in a photovoltaic system by developing and verifying nonplasmonic counterparts as an experimental control. Simple QD-sensitized solar cells (QD-SSCs) were assembled which show an 11.5% relative increase in incident photon conversion efficiency (IPCE) achieved in the plasmon-enhanced devices. We attribute this increase in IPCE to augmented charge excitation stemming from near-field "antenna" effects in the plasmonic Cu(x)In(y)S2 QD-SSCs. This study represents the first of its kind; direct interrogation of the influence of plasmon-on-semiconductor architectures with respect to excitonic absorption in photovoltaic systems.

Layered Tantalum Oxynitride Nanorod Array Carpets for Efficient Photoelectrochemical Conversion of Solar Energy: Experimental and DFT Insights

Anodically fabricated tantalum oxide (Ta2O5) nanorod array carpets are converted into the corresponding tantalum oxynitride (TaON) through nitridation in an ammonia atmosphere. The measured optical bandgap energy of TaON is ∼2.3 eV, which is also confirmed via the density functional theory calculations. When used to photoelectrochemically split water (AM 1.5G illumination, 1 M KOH, and 0.6 V applied DC bias), the multilayer nanorod films show visible-light incident photon conversion efficiencies (IPCE) as high as 7.5%. The enhanced photochemical activity is discussed in terms of the ordered one-dimensional morphology as well as the electron effective mass in TaON and Ta2O5.

Improved Visible Light Harvesting of WO3 by Incorporation of Sulfur or Iodine: A Tale of Two Impurities

We report the incorporation of sulfur or iodine into monoclinic tungsten trioxide (S:WO3 or I:WO3 respectively), with the aim to improve its visible light-harvesting ability. Films were synthesized by spray pyrolysis with either ammonium sulfide or iodide added to the aqueous WO3 precursor solutions. Red shifts of the absorption spectra were observed with S and I incorporation (from ∼2.7 to 2.6 and 2.1 eV respectively), likely due to the formation of intragap impurity bands. S:WO3 samples exhibited enhanced photoelectrochemical (PEC) performance at low S concentrations, but this quickly deteriorated with increasing S content. Incident photon conversion efficiency (IPCE) data showed that this initial improvement was driven by improved collection efficiency at longer wavelengths. Conversely, photocurrent decreased at all levels of I addition. IPCE measurements for these films showed only a marginal increase in efficiency at longer wavelengths, indicating that the extra absorbed photons did not contribute si...

Synthesis and photovoltaic properties of CuInS2/CdS quantum dots co-sensitised TiO<SUB align="right">2 photo-anodes

The CuInS 2 and CdS quantum dots co-sensitised solar cells are successfully fabricated to improve the photovoltaic performance. The CuInS 2 quantum dots are adsorbed on the surface of TiO 2 nanoparticles by assembly linking technique, and then the CdS quantum dots are deposited by successive ionic layer absorption and reaction technique. The absorption intensity is obviously enhanced and absorption edge is expanded to 800 nm after the co-sensitisation process. Under the irradiation of the simulated sunlight, the incident photon conversion efficiency (IPCE) spectra are also expanded to a longer wavelength, and the IPCE intensity reveals the maximum value of 53%. As a consequence, the photovoltaic power conversion efficiency is greatly enhanced to be 3.01%. It is mainly attributed to the better visible absorption performance from CuInS 2 quantum dots and the quantum confinement reduction of the quantum dots in these co-sensitised solar cells.

ZnSe passivation layer for the efficiency enhancement of CuInS2 quantum dots sensitized solar cells

The effect of ZnSe passivation layer is investigated in the CuInS2 quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS2 quantum dot sensitized TiO2 photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS2 quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS2 based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer.

Thermal/Electrochemical Growth and Characterization of One-Dimensional ZnO/TiO2 Hybrid Nanoelectrodes for Solar Fuel Production

One-dimensional core–shell nanostructured electrodes made of aligned TiO2 nanotubes (NTs)/ZnO were fabricated via the thermal sputtering of ZnO layers on anodically fabricated titania NTs. Increasing the ZnO sputtering time resulted in the increase in the shell thickness, which in turn showed different morphological, structural, and optical characteristics. The crystallinity of the core nanotubes was found to be a determinant factor in the formation of the NTs/ZnO heterojunctions as revealed by field emission scanning electron microscopy, glancing angle X-ray diffraction, X-ray photoelectron spectroscopy, and Raman analyses. Used as a photoanode to photoelectrochemically split water, the TiO2/ZnO heterojunction sputtered for 53 min showed an almost 80% increase in the photoconversion efficiency (7.3%) compared to that of pure TiO2 NTs (4.1%) under light illumination (320–400 nm, 100 mW/cm2, 0.5 M Na2SO4). This was confirmed via the incident photon conversion efficiency (IPCE) measurements, which showed an...

Combined Charge Carrier Transport and Photoelectrochemical Characterization of BiVO4 Single Crystals: Intrinsic Behavior of a Complex Metal Oxide

Bismuth vanadate (BiVO4) is a promising photoelectrode material for the oxidation of water, but fundamental studies of this material are lacking. To address this, we report electrical and photoelectrochemical (PEC) properties of BiVO4 single crystals (undoped, 0.6% Mo, and 0.3% W:BiVO4) grown using the floating zone technique. We demonstrate that a small polaron hopping conduction mechanism dominates from 250 to 400 K, undergoing a transition to a variable-range hopping mechanism at lower temperatures. An anisotropy ratio of ~3 was observed along the c axis, attributed to the layered structure of BiVO4. Measurements of the ac field Hall effect yielded an electron mobility of ~0.2 cm(2) V(-1) s(-1) for Mo and W:BiVO4 at 300 K. By application of the Gärtner model, a hole diffusion length of ~100 nm was estimated. As a result of low carrier mobility, attempts to measure the dc Hall effect were unsuccessful. Analyses of the Raman spectra showed that Mo and W substituted for V and acted as donor impurities. Mott-Schottky analysis of electrodes with the (001) face exposed yielded a flat band potential of 0.03-0.08 V versus the reversible H2 electrode, while incident photon conversion efficiency tests showed that the dark coloration of the doped single crystals did not result in additional photocurrent. Comparison of these intrinsic properties to those of other metal oxides for PEC applications gives valuable insight into this material as a photoanode.

LiF-doped mesoporous TiO2 as the photoanode of highly efficient dye-sensitized solar cells

This paper reports the doping of nanocrystalline TiO2 with LiF by mechanical grinding and subsequent sintering and the application of LiF-doped TiO2 as the photoanode of highly efficient dye-sensitized solar cells (DSCs). The fluoride ions can dope into the TiO2 matrix as revealed by X-ray photoelectron spectroscopy (XPS). The LiF-doped TiO2 samples are characterized by scanning electron microscopy (SEM), tunneling electron microscopy (TEM), X-ray diffraction (XRD), and UV–visible absorption spectroscopy. Doping of TiO2 with a small amount of LiF can improve the photovoltaic performance of DSCs. At the optimal LiF loading of 0.53 wt% in TiO2, the power conversion efficiency (PCE) of DSCs is enhanced from 7.74% to 8.24% under simulated AM1.5 illumination. The effect of the LiF doping on the photovoltaic performance of DSCs is investigated by electrochemical impedance spectroscopy (EIS) and incident photon conversion efficiency (IPCE) measurements. The improvement in the photovoltaic efficiency is attributed to the facilitation of the electron transport through the TiO2 electrode as a result of the increase in the anatase crystallinity induced by the LiF doping. The enhanced anatase crystallinity also causes a decrease in the charge recombination.

A Hybrid Soft Solar Cell Based on the Mycobacterial Porin MspA Linked to a Sensitizer–Viologen Diad

A prototype of a nano solar cell containing the mycobacterial channel protein MspA has been successfully designed. MspA, an octameric transmembrane channel protein from Mycobacterium smegmatis, is one of the most stable proteins known to date. Eight Ruthenium(II) aminophenanthroline-viologen maleimide Diads (Ru-Diads) have been successfully bound to the MspA mutant MspAA96C via cysteine-maleimide bonds. MspA is known to form double layers in which it acts as nanoscopic surfactant. The nanostructured layer that is formed by (Ru-Diad)8MspA at the TiO2 electrode is photochemically active. The resulting "protein nano solar cell" features an incident photon conversion efficiency of 1% at 400 nm. This can be regarded as a proof-of-principle that stable proteins can be successfully integrated into the design of solar cells.

Fabrication of Ag Nanoparticles Embedded in Al:ZnO as Potential Light-Trapping Plasmonic Interface for Thin Film Solar Cells

Incident photon conversion efficiency of the absorbing materials at either side of a thin film solar module can be enhanced by integrating a plasmonic interface. Silver nanoparticles represent a good candidate that can be integrated to a thin film solar cell for efficient light-trapping. The aim of this work is to fabricate plasmonically active interface consisting of Ag nanoparticles embedded in Al:ZnO that has the potential to be used at the front surface and at the back reflector of a thin film solar cell to enhance light-trapping and increase the photoconversion efficiency. We show that Ag can readily dewet the Al:ZnO surface when annealed at temperatures significantly lower than the melting temperature of Ag, which is beneficial for lowering the thermal budget and cost in solar cell fabrication. We find that such an interface fabricated by a simple dewetting technique leads to plasmonic resonance in the visible and near infrared regions of the solar spectrum, which is important in enhancing the conversion efficiency of thin film solar cells.

Tunable Graphene–Silicon Heterojunctions for Ultrasensitive Photodetection

We present the photodetection properties of graphene/Si heterojunctions both in the photocurrent and photovoltage modes. Monolayer graphene/Si junctions were found to be excellent weak-signal detectors with photovoltage responsivity exceeding 10(7) V/W and with noise-equivalent-power reaching ∼1 pW/Hz(1/2), potentially capable of distinguishing materials with transmittance, T = 0.9995 in a 0.5 s integration time. In the photocurrent mode, the response was found to remain linear over at least six decades of incident power (P), with tunable responsivity up to 435 mA/W (corresponding to incident photon conversion efficiency (IPCE) > 65%) obtained by layer thickening and doping. With millisecond-scale responses and ON/OFF ratios exceeding 10(4), these photodiodes are highly suitable for tunable and scalable broadband (400 < λ < 900 nm) photodetectors, photometers, and millisecond-response switching, spectroscopic and imaging devices, and further, and are architecturally compatible with on-chip low-power optoelectronics.

Enhanced efficiency of bifacial and back-illuminated Ti foil based flexible dye-sensitized solar cells by decoration of mesoporous SiO2 layer on TiO2 anode

The present study focuses on enhancing the efficiency of bifacial and back-illuminated dye-sensitized solar cells (DSCs) by incorporating SiO2 mesoporous layer on TiO2 electrode. The performance of DSCs is investigated by UV–visible spectroscopy, incident photon conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS). It is observed that the current ratio of back- to front-DSC increases with the increase in the thickness of SiO2 layer, which in turn influences the incident light to dyed-TiO2 electrode, especially in the wavelength of 400–600 nm. The Ti foil based flexible small (0.28 cm2) and sub-module (5 cm × 10 cm) DSCs having this modification show high conversion efficiencies of 6.76 and 5.54% respectively under 100 mW cm−2 (AM 1.5).

Efficient and stable back-illuminated sub-module dye-sensitized solar cells by decorating SiO2 porous layer with TiO2 electrode

The present study focuses on enhancing the efficiency of back-illuminated dye-sensitized solar cells (DSCs) by incorporating a SiO2 mesoporous layer on a TiO2 electrode. The performance of the DSCs is investigated by incident photon conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS). It is observed that the photocurrent increases when the TiO2 electrode is coated with a SiO2 layer, resulting in an increase in the incident light to the dye–TiO2 electrode, especially in the wavelength range 400–600 nm. The TiO2 electrode coated with 500 nm diameter mesoporous SiO2 exhibits better device performance than that using 100 nm diameter SiO2 particles. With this modification, the Ti foil-based flexible sub-module DSC (5 cm × 10 cm) shows a high conversion efficiency of 7.13% under illumination of 100 mW cm−2 (AM 1.5), as well as good stability.

Physical and photoelectrochemical characterization of Ti-doped hematite photoanodes prepared by solution growth

We present the fabrication and characterization of Ti-doped hematite (α-Fe2O3) films for application as photoanodes in photoelectrochemical (PEC) cells for water splitting. It is demonstrated that Ti doping significantly improves the PEC activity as the photocurrent at 1.0 V vs. Ag/AgCl electrode for a 400 nm thick Ti-doped film (0.66 mA cm−2) was found to be ∼14 times higher than that of an undoped film (0.045 mA cm−2). The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultrafast transient absorption spectroscopy to obtain information about their structural, electronic, and charge carrier dynamic properties. Based on characterization of the chemical states of the involved elements as well as the charge carrier dynamics of the films with Ti doping, it appears that the photocurrent enhancement is related to an increase in charge carrier density or reduced electron–hole recombination. The highest incident photon conversion efficiency (IPCE) measured for this system was 27.0% at 360 nm at a potential of 1.23 V vs. reversible hydrogen electrode (RHE), which was obtained on a 400 nm thick Ti-doped α-Fe2O3 film.

Light absorption enhancement in polymer solar cells with nano-Ag

The thickness of an active layer is limited by its low mobility of carriers in a polymer solar cell composed of the blend bulk-heterojunction formed by P3HT as donor material and PCBM as acceptor material, which can affect the light absorption of the polymer solar cell. Metal nanocrystals-doped polymer active layer can enhance its inner electrical field and absorb light due to the surface plasmon resonance (SPR) effect of the nanocrystals. Two-dimensional electrical field distributions in the polymer solar cells are simulated based on finite difference time domain (FDTD) approach, under the assumption that the diameter of doping nano-Ag is 50 nm, the distance between two nanocrystals is 50nm and the incident light wavelength is 400 nm or 500 nm. The electrical field distributions over the cross-section of nano-Ag are also simulated at the incident light angle of 15°, 45°, 60°, respectively. The light absorption of different devices are calculated, in which the sizes of nano-Ag take 10 nm, 20 nm and 50 nm, respectively, Particles of nano-Ag are dispersed in PEDOT:PSS layer. Moreover, the light absorption is calculated at the incident light angles of 15°, 45°, 60°, respectively. Results show that the electrical field is redistributed due to the SPR effect caused by nano-Ag in the polymer active layer. A larger size of nano-Ag leads to light scattering in a wider angle, thus results in more light absorption by the device. Here, the colloid of nano-Ag is prepared from an organic salt of Ag, and the polymer solar cell with nano-Ag is fabricated in the structure of glass /ITO (～100 nm) /PEDOT:PSS (40 nm) /P3HT:PCBM (～100 nm)/(nano-Ag) /LiF (1 nm) /Al (120 nm). Furthermore, experimental results show that the nano-Ag doped in P3HT:PCBM layer increases light absorption and improves the electrical performance of the device, which enhances the incident photon conversion efficiency (IPCE) in spectrum at 520nm by 17.9%.

Charge carrier separation in nanostructured TiO2 photoelectrodes for water splitting

There is intense interest in developing new novel nanostructured photoanodes for water splitting. It is therefore important that methods to analyze the effect of nanostructuring on water splitting yields are developed in order to rationalize the relative merits of this approach for different materials. In this study the dependence of charge separation efficiency (η(sep)) on potential during photoelectrochemical water splitting at pH 2 has been quantified in a model electrode system (nanocrystalline, mesoporous TiO2) using two independent methods. These are (i) analysis of incident photon conversion efficiency (IPCE) measurements and (ii) transient absorption (TA) spectroscopy measurements. The techniques provide good agreement with each other and show that a low maximum value of η(sep) (~0.18) is the primary cause of the low IPCE for water oxidation on these nc-TiO2 electrodes.

Spray Pyrolysis Deposition and Photoelectrochemical Properties of n-Type BiOI Nanoplatelet Thin Films

Bismuth oxy-iodide is a potentially interesting visible-light-active photocatalyst; yet there is little research regarding its photoelectrochemical properties. Herein we report the synthesis of BiOI nanoplatelet photoelectrodes by spray pyrolysis on fluorine-doped tin oxide substrates at various temperatures. The films exhibited n-type conductivity, most likely due to the presence of anion vacancies, and optimized films possessed incident photon conversion efficiencies of over 20% in the visible range for the oxidation of I(-) to I(3)(-) at 0.4 V vs Ag/AgCl in acetonitrile. Visible-light photons (λ > 420 nm) contributed approximately 75% of the overall photocurrent under AM1.5G illumination, illustrating their usefulness under solar light illumination. A deposition temperature of 260 °C was found to result in the best performance due to the balance of morphology, crystallinity, impurity levels, and optical absorption, leading to photocurrents of roughly 0.9 mA/cm(2) at 0.4 V vs Ag/AgCl. Although the films performed stably in acetonitrile, their performance decreased significantly upon extended exposure to water, which was apparently caused by a loss of surface iodine and subsequent formation of an insulating bismuth hydroxide layer.

Photoelectrochemical water splitting at nanostructured α-Fe2O3 electrodes

In this study, nanostructured α-Fe2O3 thin films were deposited by simple electrodeposition for photoelectrochemical water splitting. Post-annealing temperature was found to have drastic effect on photoactivity of these films. SEM analysis illustrated that size of nanoparticles increases with annealing temperature. The current–potential characteristics showed that the water-splitting photocurrent strongly depends on post-annealing temperature. A maximum photocurrent density of 0.67 mA/cm2 was observed at 1.23 V versus reversible hydrogen electrode (RHE) under standard illumination conditions (AM 1.5 G 100 mW/cm2), and the water-splitting current was over 1.0 mA/cm2 before the dark current flow starts (at 1.55 V versus RHE). The electrode shows an onset potential as low as 0.8 V (versus RHE) for water photooxidation, which is one of the best results reported for hematite photoanodes. This high photoactivity of electrodes is attributed to the preferential growth of hematite nanostructures along the most conductive plane (001) and incorporation of Sn in film from the substrate at high annealing temperature. The best-performing electrode shows an incident photon conversion efficiency (IPCE) of 12% at 400 nm (in 1 M NaOH at 1.23 V versus RHE), which indicate the improved light-harvesting properties of these nanostructures.