Photocurrent Yield Research Articles

Sn-Doped Hematite Films as Photoanodes for Photoelectrochemical Alcohol Oxidation

Here, the modification of semiconductor thin film hematite photoanode by doping with Sn ions is reported. Undoped and Sn-doped hematite films are fabricated by the electrochemical deposition of FeOOH from aqueous alkaline electrolyte, followed by calcination in air. The photoanodes were tested in photoelectrocatalytic oxidation of water, methanol, ethylene glycol, and glycerol. It is shown that modification by tin dramatically increased the activity of hematite in the photoelectrochemical oxidation of alcohols upon visible light irradiation. The photoelectrocatalytic activity of Sn-modified hematite increased in the sequence of: H2O < MeOH < C2H2(OH)2 < C3H5(OH)3. The quantum yield of photocurrent in the oxidation of alcohols reached 10%. The relatively low photocurrent yield was ascribed to the recombination of photoexcited holes within the hematite layer and on surface states located at the hematite/electrolyte interface. Intensity-modulated photocurrent spectroscopy (IMPS) was used to quantify the recombination losses of holes via surface states. The IMPS results suggested that the hole acceptor in the electrolyte (alcohol) influences photocurrent both by changing the charge transfer rate in the photoelectrooxidation process and by the efficient suppression of the surface recombination of generated holes. Thin-film Sn-modified hematite photoanodes are promising instruments for the photoelectrochemical degradation of organic pollutants.

Photocurrent Generation Properties of Half-Photocell Consisting of Electropolymerized Hierarchical Polythiophene Thin Films as Photoexciting Electron Donor and C60 as Electron Acceptor

Polybithiophene/poly(3,4-ethylenedioxythiophene)/indium-tin-oxide coated transparent glass electrodes were prepared by sequential electrochemical polymerization with cyclic voltammetry. The thickness of polybithiophene films was varied by the scan rate of applied potentials during polymerization. Obtained hierarchical polythiophene films were characterized by absorption spectra, fluorescence spectra, scanning electron microscopy, laser microscopy, and atomic force microscopy. Half-photocell properties of the hierarchical polythiophene thin films were evaluated by a three-electrode electrochemical cell in CH2Cl2 solution of electrolyte and C60 as a sacrificial electron acceptor under irradiation of monochromatic light. The thickness and absorbance of hierarchical polythiophene thin films increased by decreasing of scan rate of applied potentials during the polymerization of polybithiophene. While, maximum peaks of fluorescence intensity and internal quantum yield of cathodic photocurrent were observed at 20 nm thickness of polythiophene film under irradiation from the glass side of the transparent electrode. Almost maximum external quantum efficiencies of cathodic photocurrent were observed from 20 nm to 1.5 μm thicknesses of polythiophene films. These tendencies suggest that CH2Cl2 solution of C60 and electrolyte penetrate into the polybithiophene layer up to 1.5 μm.

Laser-Synthesized 2D-MoS2 Nanostructured Photoconductors.

The direct laser synthesis of periodically nanostructured 2D transition metal dichalcogenide (2D-TMD) films, from single source precursors, is presented here. Laser synthesis of MoS2 and WS2 tracks is achieved by localized thermal dissociation of Mo and W thiosalts, caused by the strong absorption of continuous wave (c.w.) visible laser radiation by the precursor film. Moreover, within a range of irradiation conditions we have observed occurrence of 1D and 2D spontaneous periodic modulation in the thickness of the laser-synthesized TMD films, which in some cases is so extreme that it results in the formation of isolated nanoribbons with a width of ~200 nm and a length of several micrometers. The formation of these nanostructures is attributed to the effect that is known as laser-induced periodic surface structures (LIPSS), which is caused by self-organized modulation of the incident laser intensity distribution due to optical feedback from surface roughness. We have fabricated two terminal photoconductive detectors based on nanostructured and continuous films and we show that the nanostructured TMD films exhibit enhanced photo-response, with photocurrent yield increased by three orders of magnitude as compared to their continuous counterparts.

Highly efficient functional materials for modern electrochemical devices

In order to find new functional materials and materials with improved performance for next-generation electrochemical devices, several new materials for various purposes have been synthesized. In particular, BiVO4 films were obtained by electrochemical synthesis using interferometric control of film thickness during their deposition. Previously, it was found that the use of thin BiVO4 films with a thickness of 150 to 400 nm is most effective, where an increase in the quantum yield of photocurrent up to 0.25 at ? of 400 to 450 nm was observed. LiFePO4 was synthesized in DES medium (low-temperature eutectic solvents): choline chloride?triethylene glycol (ChCl?TEG) and choline chloride?ethylene glycol (ChCl?EG) using NH4FePO4 and CH3COOLi as precursors. It was found that the mode of synthesis of LiFePO4/C at 973 ? for 1 h does not lead to oxidation of LiFePO4, as evidenced by the values of the ratio Fe2+/Fe3+ for LiFePO4 and LiFePO4/C, which are 2.4 and 2.7, respectively. It was found that the substitution of a part of lead cations (up to 20 mol. %), in the composition of the fluoride-conducting phase Pb0.86Sn1.14F4, contributes to the increase of its conductivity in the whole temperature range, the higher the concentration of the substituent, to a greater extent. Charge transfer is provided by highly mobile interstitial fluorine anions, the concentration of which increases with the rise of temperature and substituent content.

Photoelectrochemical determination of Pb2+ by combined electrochemical-chemical precipitations of PbI2 films

• Combined method of chemical and electrochemical depositions films of PbI 2 . • Photoelectrochemical content definition of Pb 2+ by photocurrent magnitude of PbI 2 thin films. • Selective photoelectrochemical definition of Pb 2+ in acidic nitrate solutions. A simple and inexpensive method of selective photoelectrochemical determination of Pb 2+ content in acidic nitrate solutions has been developed, which can be used to control the lead content in wastes of the chemical industry and processing industry. For selective photoelectrochemical determination of lead concentration, studies of the effect of time and current of electrodeposition, oxide compounds of lead and conditions of conversion PbO 2 into PbI 2 on a glass/SnO 2 substrate were performed. The main objective of these studies was to determine the relationship between the photosensitivity of PbI 2 films and time and current of PbO 2 electrodeposition in solutions with different amounts of lead ions. From the analysis of interferometric studies of electrochemical growth PbO 2 films and PbI 2 quantum yield spectra of photocurrent, the optimal values of time and current of electrodeposition were established. Established of dependency quantum yield of photocurrent of lead concentration products in the form of PbI 2 thin films depends on the thickness of electrodeposited PbO 2 , which in turn depends directly on the concentration of Pb 2+ ions in the analyzed solution. It was found that sensitivity of method can reach 0.05 mg/L (Pb 2+ ).

Morphological-Electrical Property Relation in Cu(In,Ga)(S,Se)2 Solar Cells: Significance of Crystal Grain Growth and Band Grading by Potassium Treatment.

Solution-processed Cu(In,Ga)(S,Se)2 (CIGS) has a great potential for the production of large-area photovoltaic devices at low cost. However, CIGS solar cells processed from solution exhibit relatively lower performance compared to vacuum-processed devices because of a lack of proper composition distribution, which is mainly instigated by the limited Se uptake during chalcogenization. In this work, a unique potassium treatment method is utilized to improve the selenium uptake judiciously, enhancing grain sizes and forming a wider bandgap minimum region. Careful engineering of the bandgap grading structure also results in an enlarged space charge region, which is favorable for electron-hole separation and efficient charge carrier collection. Besides, this device processing approach has led to a linearly increasing electron diffusion length and carrier lifetime with increasing the grain size of the CIGS film, which is a critical achievement for enhancing photocurrent yield. Overall, 15% of power conversion efficiency is achieved in solar cells processed from environmentally benign solutions. This approach offers critical insights for precise device design and processing rules for solution-processed CIGS solar cells.

New insights into the structure of two-dimensional lead iodide-based perovskites

This paper reports a comprehensive investigation of 2D and quasi-2D perovskites that are based on rather long-chain octylammonium iodide (OA) and have the a general formula (OA)2(MA)n, PbnI3n+1. Surprisingly, we noticed for 2D and quasi-2D perovskites the presence of significant amounts of the lead state having unusually low binding energy for Pb2+ which resembles unsaturated-valence Pb0 species. The low binding energy of Pb reflects the more electron-rich (compared to 3D counterparts) environment around the Pb centers of the 2D perovskites, which is their inherent property and a consequence of a distinctly different chemical compositions of 2D compared to 3D perovskites. It was found that 2D perovskite-based photodetectors having a lateral arrangement of electrodes show a superior photocurrent yield, compared to quasi-2D (n = 2,3) and 3D (n = ∞) perovskites. Furthermore, 2D and 3D perovskite films exhibit comparable conductivity in the vertical direction, despite of a high content of the insulating component in the OA-based 2D perovskites. The high conductivity was attributed to excellent film-forming properties, high environmental stability as well as favored charge transport morphology of 2D perovskite films. We also propose that inclusions of PbI2 in the organic interlayers may explain the improved charge transportation in these materials. Cross-sectional analysis of the perovskite films and spatially-resolved conductive mode atomic force microscopy measurements support this assumption. • 2D perovskite (C8H17NH3)2 PbI4 contain comparable amounts of Pb(II) and Pb(0). • In contrast, 3D perovskites contain only Pb(II) lead state. • Lateral 2D perovskite photodetectors outperform 3D perovskite-based counterparts. • 2D and 3D perovskite films have comparable conductivity in the vertical direction. • Inclusions of PbI2 in the organic interlayers may explain the high vertical conductivity.

Variations in the Composition of the Phases Lead to the Differences in the Optoelectronic Properties of MAPbBr3 Thin Films and Crystals

Photoluminescence (PL) spectra from thin films (TFs) and bulk crystals (BCs) of hybrid organo-halide perovskites are significantly different, the origin of which and their impact on the efficiency of the perovskite-based photoactive devices have been debated. We have used two-photon PL to study the temperature-dependent changes in the spectra of the TFs and the BCs of methylammonium lead bromide (MAPbBr3) perovskites in order to clarify the origin of the differences. Our results show that the differences in the spectra are due to the variation in the phase composition. At room temperature, the tetragonal (TE) phase is dominant in the BCs, while the orthorhombic (OR) phase is dominant in the TFs. The PL spectra of the TFs also show discernible contributions from the TE and the cubic phases. At lower temperatures, the increase in excitonic recombination causes a red shift of the PL spectra from the TFs, while a phase transition from the TE to the OR phase results in a blue shift of the PL from the BCs. The temperature-dependent narrowing of the PL linewidths shows a stronger coupling between the longitudinal optical phonons and the free carriers in the OR phase as compared to the TE phase, implying a reduced carrier mobility. However, as the OR phase is metastable at the room temperature, the slow phase transition to the TE phase should improve the photocurrent yield in the TFs, provided that the sample is shielded from other types of degradation.

Optically Generated Free-Carrier Collection from an All Single-Walled Carbon Nanotube Active Layer.

Semiconducting single-walled carbon nanotubes' (SWCNTs) broad absorption range and all-carbon composition make them attractive materials for light harvesting. We report photoinduced charge transfer from both multichiral and single-chirality SWCNT films into atomically flat SnO2 and TiO2 crystals. Higher-energy second excitonic SWCNT transitions produce more photocurrent, demonstrating carrier injection rates are competitive with fast hot-exciton relaxation processes. A logarithmic relationship exists between photoinduced electron-transfer driving force and photocarrier collection efficiency, becoming more efficient with smaller diameter SWCNTs. Photocurrents are generated from both conventional sensitization and in the opposite direction with the semiconductor under accumulation and acting as an ohmic contact with only the p-type nanotubes. Finally, we demonstrate that SWCNT surfactant choice and concentration play a large role in photon conversion efficiency and present methods of maximizing photocurrent yields.

Two‐dimensional Mixed Phase Leaf‐Ti1‐xCuxO2 Sheets Synthesized Based on a Natural Leaf Template for Increased Photocatalytic H2 Evolution

AbstractTwo‐dimensional (2D) leaf‐TiO2 (LTiO2) nano sheets were synthesized using a natural leaf template. In addition, 2D mixed phase leaf‐Ti1‐xCuxO2 sheets (1CuLTiO2) were prepared by incorporating Cu ions (1 wt %) into the LTiO2 lattice using a deposition‐precipitation method followed by a calcination process. Structural microscopic and spectroscopic analyses demonstrated the generation of anatase and rutile surface‐phase junctions as well as the combination of Cu ions with the disordered mesoporous leaf‐TiO2 lattice. Hydrogen evolution reactions over 1CuLTiO2 materials were performed using methanol as a sacrificial reagent under one sun illumination. LTiO2‐750, synthesized by calcination at 750 °C, showed an absorption onset at 410 nm, while LTiO2‐550, synthesized by calcination at 550 °C, exhibited an onset at 387 nm. Cu incorporation into the 1CuLTiO2‐750 lattice, synthesized by calcination at 750 °C, led to the increase in the visible light absorption. Both the photocurrent and hydrogen yield via 1CuLTiO2‐750 (apparent quantum yield, 4.9 %) were higher than the respective values of 1CuLTiO2‐550 (AQY=2.9 %) synthesized by calcination at 550 °C, highlighting the importance of the surface‐phase junction. The increased photocatalytic activity of 1CuLTiO2‐750 was mainly assigned to the formation of surface‐phase junctions, disordering mesoporosity, and 2D sheet morphology for fast charge carriers.

Niobium and iron co-doped titania nanobelts for improving charge collection in dye-sensitized TiO2 solar cells

Niobium (Nb) and iron (Fe) co-doped titanium oxide nanobelts were prepared in a one-pot alkaline hydrothermal process followed by calcination treatment, and evaluated in TiO2 nanoparticle-based composite anodes for dye-sensitized solar cells. Addition of Nb and Fe species caused an increase in donor density and trap-mediated charge transition, as characterized by electrochemical and photoluminescence analyses. Under illumination with simulated solar light, the co-doped single-crystalline nanobelts promoted photocurrent yield and open-circuit voltage, because they facilitate electronic conduction and chemical capacitance in the composite anodes. This improved photovoltaic performance is associated with the enhanced charge collection efficiency, mechanistically attributed to rapid electron transport and prolonged electron lifetime via shallow trapping sites. Results demonstrate that the Nb and Fe co-doped titania nanobelts are effective to provide longer electron diffusion lengths and favor charge accumulation during cell operation.

Efficient promotion of charge separation with reduced graphene oxide (rGO) in BiVO4/rGO photoanode for greatly enhanced photoelectrochemical water splitting

Although BiVO4 (BVO) continues to attract strong attention as an ideal reactive semiconductor, its photoelectrochemical (PEC) water splitting performance remains low because most of the charge carriers are easily recombined in the bulk or on the surface of the photoanode before reaching the fluorine-doped tin dioxide (FTO). This study presents a facile and simple, visible-light-assisted, photocatalytic reduction of graphene oxide (GO) by using BVO for the preparation of highly stable BVO/reduced GO (rGO) nanocomposites with two different rGO weight ratios (5% and 10%). These as-prepared BVO/rGO nanocomposites were then drop-cast on an FTO substrate to demonstrate the key role played by the rGO in greatly improving the electron transport in the BVO/rGO films. In PEC water splitting experiments, the BVO/rGO-10% photoelectrode showed the highest photocurrent density (554.4 µA cm−2 at 1.2 V vs. Ag/AgCl), compared to BVO (111.7 µA cm−2) and BVO/rGO-5% (377.9 µA cm−2). The stable BVO/rGO also showed the highest charge carrier density, with an extended lifetime and improved the electrical conductivity, as compared to BVO. These results contributed to the excellent PEC performance of the BVO/rGO photoanode. Under simulated solar light illumination, the open-circuit potential (OCP) of the BVO/rGO films was shifted to a more negative value due to the enhanced electron-hole separation in the films. The photocurrent yields of the BVO and BVO/rGO electrodes were dependent on the solution pH. The photocurrent densities were higher over the full range of measured potential (0 to + 1.2 V vs. Ag/AgCl) in the NaOH electrolyte (1 M, pH = 13.5) than in the Na2SO4 electrolyte (0.1 M, pH = 6.5). This work demonstrates the essential role of the rGO coverage in the great enhancement of electron transport through the rGO in the BVO/rGO film.

Graphene-CdSe quantum dot hybrid as a platform for the control of carrier temperature

In a graphene and quantum dots (QDs) hybrid structure, the graphene is known to play the role of an electrode that conducts the photoexcited carriers from the QDs to the electrodes. Thus, the yield of photocurrent of the QD ensemble is greatly enhanced [1]. However, in our study, the graphene provides a platform to control the energy relaxation of optically excited carriers from QDs. Thus, the temperature of photocarriers of QDs is controllable. Due to the moderate carrier temperature, the observed photocurrent from the hybrid structure reveals a photothermoelectric effect, which becomes even stronger when the Fermi energy, EF, is located near the charge neutrality point (CNP) of the graphene. However, the photothermoelectric behavior weakens with increased EF. Such a behavior originates from the varying electron-phonon coupling strength that is dependent upon EF of the graphene.

Surface modification of NiCdO barrier layer in complex photoanodes and TiO2 protective coating for efficient and stabile water dissociation

This work presents a follow-up research of our previously published work. Herein, the photocatalytic performance of a nanostructured CdZnO/NiCdO composite photoanode has been improved by intercalation of Cu catalyst atoms in the electron barrier layer of NiyCd1−yO surface by an ion exchange process. As a result, the photocurrent yield increased by 29 % at +1 V potential against Ag/AgCl. This phenomenon was tentatively attributed to the increased electron concentration and/or interaction of the Cu3d electrons with the mid-energy valence electrons. To the contrary, the introduction of Ag, Co, and Ni deteriorated the photocatalytic performance. The corrosion challenges were assessed during 50 cycles of voltammetry. The background of the degradation/photocorrosion was studied with SEM, EDX, and XPS analysis. To combat the photocorrosion, the photoanodes were coated with TiO2 protective nanolayers of different thickness. The results for the photocurrent stability at a constant potential of +1 V showed that 9 nm TiO2 coating improved the durability of the photoanode on account of a photocurrent decrease for about 50 %. XPS studies proved that the degradation/corrosion changes on the photoanode’s surface could be associated with an irreversible electrochemical oxidation of CdO into CdO2.

(Invited) New Photocurrent Generating Pathways in Twisted Bilayer Graphene and Stacked Transition Metal Dichalcogenide Materials

The high-conductivity, low cost and relative ease of fabrication have made graphene well-suited to transform nanoscale electronics. Unfortunately, as a gapless semimetal, photo-excited electrons in graphene recombine far faster than electron-hole pairs can be extracted.[1] To make carrier lifetimes in 2D materials more competitive with carrier separation, we demonstrate promising, new electron extraction pathways in graphene-like systems including twisted bilayer graphene (tBLG) and transition metal dichalcogenides (TMD). In tBLG, we show the emergence of twist angle-tunable excitonic absorption peaks that result from the rehybridization of constrained interlayer 2p orbitals[2]. Specifically, we use one and two-photon transient absorption microscopy to directly image the predicted[3] bright and dark stable, strongly-bound excitons states. This observation of strongly bound excitons is a first for a 2D metallic system, and serves to substantially increase graphene’s carrier lifetime, suggesting new pathways for photocurrent collection. Unlike graphene, semiconducting 2D TMDs like WSe2, have long carrier lifetimes, but challenging mobility and exciton dissociation bottlenecks that inhibit photocurrent generation. By combining femtosecond resolved photocurrent microscopy[1,4] with ultrafast transient absorption, we have selectively imaged the dominant kinetics bottlenecks that inhibit photocurrent production in devices made from WSe2TMD materials. Using these ultrafast space-time maps of the electron-hole dissociation dynamics, we hope to better engineer 2D material heterostructures devices to avoid efficiency-destroying, carrier recombination bottlenecks and maximize photocurrent yield. (1) M.W. Graham, S. Shi, D.C. Ralph, J. Park, P.L. McEuen (2013), Nature Physics, 9, 103 (2) H. Patel, R. Havener, L. Brown, Y. Liang, L. Yang, J. Park, M.W. Graham (2015), Nano Letters, 15, 5932-7 (3) Y. Liang, R. Soklaski, S. Huang, M.W. Graham, R. Havener, J. Park, L. Yang (2014), Phys Rev B, 90, 115418 (4) M. Massicotte, P. Schmidt, F. Vialla, K. G. Schädler, A. Reserbat-Plantey, K. Watanabe, T. Taniguchi, K.-J. Tielrooij, and F. H. L. Koppens (2015), arXiv:1507.06251 [cond-mat]

Effect of Molecular Stacking on Exciton Diffusion in Crystalline Organic Semiconductors.

Exciton diffusion is at the heart of most organic optoelectronic devices' operation, and it is currently the most limiting factor to their achieving high efficiency. It is deeply related to molecular organization, as it depends on intermolecular distances and orbital overlap. However, there is no clear guideline for how to improve exciton diffusion with regard to molecular design and structure. Here, we use single-crystal charge-transfer interfaces to probe favorable exciton diffusion. Photoresponse measurements on interfaces between perylenediimides and rubrene show a higher photocurrent yield (+50%) and extended spectral coverage (+100 nm) when there is increased dimensionality of the percolation network and stronger orbital overlap. This is achieved by very short interstack distances in different directional axes, which favors exciton diffusion by a Dexter mechanism. Even if the core of the molecule shows strong deviation from planarity, the similar electrical resistance of the different systems, planar and nonplanar, shows that electronic transport is not compromised. These results highlight the impact of molecular organization in device performance and the necessity of optimizing it to take full advantage of the materials' properties.

Dynamics of Charge Generation and Transport in Polymer-Fullerene Blends Elucidated Using a PhotoFET Architecture

High efficiency polymer-fullerene bulk heterojunction organic solar cells can generate photocurrent by excitation of the electron donor and acceptor components via Channel I and Channel II processes, respectively. Using a planar Photo-Field-Effect-Transistor (PhotoFET) architecture operated in steady state and quasi-transient modes we have studied the dynamics of charge generation and transport in blends of PCDTBT/70-PCBM (poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-{4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole}]/[6,6]-phenyl-C71-butyric acid methylester). The PhotoFET architecture allows independent measurement of the electron and hole photocurrents and mobilities for charge carriers generated by the Channel I (electron transfer) and Channel II (hole transfer) processes as a function of fullerene content. We find dramatic increases in the photocurrent yield and electron mobility with higher 70-PCBM loading. By analyzing the External Quantum Efficiency (EQE) in n- and p-PhotoFET modes, we estimate that 8...

Barrier Height Measurement of Metal Contacts to Si Nanowires Using Internal Photoemission of Hot Carriers

Barrier heights between metal contacts and silicon nanowires were measured using spectrally resolved scanning photocurrent microscopy (SPCM). Illumination of the metal-semiconductor junction with sub-bandgap photons generates a photocurrent dominated by internal photoemission of hot electrons. Analysis of the dependence of photocurrent yield on photon energy enables quantitative extraction of the barrier height. Enhanced doping near the nanowire surface, mapped quantitatively with atom probe tomography, results in a lowering of the effective barrier height. Occupied interface states produce an additional lowering that depends strongly on diameter. The doping and diameter dependencies are explained quantitatively with finite element modeling. The combined tomography, electrical characterization, and numerical modeling approach represents a significant advance in the quantitative analysis of transport mechanisms at nanoscale interfaces that can be extended to other nanoscale devices and heterostructures.

Effect of Post-Annealing Treatment on Photocatalytic and Photoelectrocatalytic Performances of TiO<SUB>2</SUB> Nanotube Arrays Photoelectrode

Highly ordered TiO2 nano-tube arrays (TNTAs) photoelectrodes were prepared through anodization method, followed by annealing treatment. Morphologies and structures of the as-prepared TNTAs samples were investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, the optical and photoelectrochemical (PECH) properties were investigated through ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and transient photocurrent response. Furthermore, the photodecomposition performances were investigated through the yield of hydroxyl (*OH) radicals and photocatalytic (PC) degradation of RhB under Xenon light irradiation. Results indicated that the TNTAs samples annealed at 723 K exhibited the highest photocurrent response, PC performance and yield of *OH radicals, in which 60.8% of RhB could be degraded by PC degradation within 60 min. The high PC performance could mainly be attributed to the anatase structure, high crystallinity and highly ordered nano-tubular structure, which favored the transfer and separation of photoinduced charge carriers. This study suggests that highly ordered nano-structure could provide superior pathway for the charge transfer and separation.

Iron-doped titania thin films with enhanced photovoltaic efficiency: Effects of iron concentration and rectifying layer

Iron-doped titania thin films were fabricated by spin-coating from sol–gel pastes of iron nitrate and titanium isopropoxide and evaluated for photovoltaic conversion in a solar cell. The Fe addition induced a red shift in optical absorption, an electronic interaction between Fe and Ti atoms and an increase in donor density, indicating the excitation of electrons from Fe donors. All Fe-added titania films were shown more hydrophilic than the titania film and produced higher photocurrents when irradiated by visible light. Under ultraviolet illumination, low amounts of Fe dopants promoted photocurrent yield because they served as electron traps for enhancing charge carrier separation, and the yield was lowered at higher Fe concentrations due to charge carrier recombination at Fe sites. Increasing Fe content led to a decrease in open-circuit photovoltage. Addition of a Fe–TiO2 film between the TiO2 layer and the conductive substrate caused a marked increase in photocurrent. The improved cell performance is related to the behavior of rectifying electron flow through two oxide layers, composed of electron transfer and diffusion. Results demonstrate that the Fe doping provides photoactive traps to mediate electron transport for enhancing quantum conversion efficiency. Mechanistic aspects about the role of the Fe traps are discussed.