The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Frank E Osterloh - One of the best experts on this subject based on the ideXlab platform.
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use of surface Photovoltage spectroscopy to probe energy levels and charge carrier dynamics in transition metal ni cu fe mn rh doped srtio3 photocatalysts for h2 evolution from water
Journal of Materials Chemistry, 2018Co-Authors: Xiaoli Cui, Zeqiong Zhao, Mauricio A Melo, Emily J Roberts, Frank E OsterlohAbstract:Doping with transition metal ions is widely employed to adjust the optical and photocatalytic properties of wide band semiconductors, however, quantitative information about the energetics and charge transfer dynamics of the impurity states is often difficult to obtain. Here we use surface Photovoltage spectroscopy (SPS), optical spectroscopy, and irradiation experiments to study the effect of several dopants on the ability of SrTiO3 nanocrystals to generate a Photovoltage and to catalyse H2 evolution from aqueous methanol. Phase pure SrTiO3:TM nanocrystals with TM = Ni, Cu, Fe, Mn, Rh were synthesized by hydrothermal reaction of TiO2, Sr(OH)2, KOH, and transition metal chlorides and nitrates in water. SPS data was obtained on thin films of these nanocrystals on fluorine doped tin oxide substrates under vacuum atmosphere. All samples are n-type, which can be gauged from the negative Photovoltage caused by the transfer of electrons into the FTO substrate. All dopants produce sub-bandgap states in the SrTiO3 lattice, whose energetic positions can be determined from the Photovoltage onset energy in SPS and from optical absorption spectra. The reversibility and size of the Photovoltage provide information about the photohole dynamics and their ability to oxidize sacrificial electron donors at the nanocrystal surface. Overall, this work provides an explanation for the inability of Ni, Cu, Fe, Mn dopants to enhance visible light photocatalytic activity in SrTiO3, and it establishes SPS as a useful tool to map the energetics and photochemistry of impurity states in metal oxide nanocrystals.
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surface Photovoltage measurements on a particle tandem photocatalyst for overall water splitting
Nano Letters, 2018Co-Authors: Alexandra T. De ,denko, Benjamin A Nail, Mauricio A Melo, Ana Flavia Nogueira, Frank E OsterlohAbstract:Surface Photovoltage spectroscopy (SPS) is used to measure the photopotential across a Ru–SrTiO3:Rh/BiVO4 particle tandem overall water splitting photocatalyst. The tandem is synthesized from Ru-modified SrTiO3:Rh nanocrystals and BiVO4 microcrystals by electrostatic assembly followed by thermal annealing. It splits water into H2 and O2 with an apparent quantum efficiency of 1.29% at 435 nm and a solar to hydrogen conversion efficiency of 0.028%. According to SPS, a Photovoltage develops above 2.20 eV, the effective band gap of the tandem, and reaches its maximal value of −2.45 V at 435 nm (2.44 mW cm–2), which corresponds to 96% of the theoretical limit of the photocatalyst film on the fluorine-doped tin-oxide-coated glass (FTO) substrate. Charge separation is 82% reversible with 18% of charge carriers being trapped in defect states. The unusually strong light intensity dependence of the Photovoltage (1.16 V per decade) is attributed to depletion layer changes inside of the BiVO4 microcrystals. These fin...
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use of surface Photovoltage spectroscopy to measure built in voltage space charge layer width and effective band gap in cdse quantum dot films
Journal of Physical Chemistry Letters, 2016Co-Authors: Jing Zhao, Benjamin A Nail, Michael A Holmes, Frank E OsterlohAbstract:Surface Photovoltage spectroscopy (SPS) was used to study the photochemistry of mercaptoethanol-ligated CdSe quantum dot (2.0–4.2 nm diameter) films on indium doped tin oxide (ITO) in the absence of an external bias or electrolyte. The n-type films generate negative voltages under super band gap illumination (0.1–0.5 mW cm–2) by majority carrier injection into the ITO substrate. The Photovoltage onset energies track the optical band gaps of the samples and are assigned as effective band gaps of the films. The Photovoltage values (−125 to −750 mV) vary with quantum dot sizes and are modulated by the built-in potential of the CdSe–ITO Schottky type contacts. Deviations from the ideal Schottky model are attributed to Fermi level pinning in states approximately 1.1 V negative of the ITO conduction band edge. Positive Photovoltage signals of +80 to +125 mV in films of >4.0 nm nanocrystals and in thin (70 nm) nanocrystal films are attributed to electron–hole (polaron) pairs that are polarized by a space charge ...
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photochemical charge transfer observed in nanoscale hydrogen evolving photocatalysts using surface Photovoltage spectroscopy
Energy and Environmental Science, 2015Co-Authors: Jiarui Wang, Jing Zhao, Frank E OsterlohAbstract:The application of inorganic nanostructures for solar water splitting is currently limited by our understanding of photochemical charge transfer on the nanoscale, where space charge layers are less effective for carrier separation. Here we employ surface Photovoltage spectroscopy to measure the internal Photovoltages in single crystalline platinum/ruthenium-modified Rh-doped SrTiO3 nanocrystals for the first time. Voltages of −0.88 V and −1.13 V are found between the absorber and the Ru and Pt cocatalysts, respectively, and a voltage of −1.48 V for a Rh:SrTiO3 film on an Au substrate. This shows that the Pt and Ru cocatalysts not only improve the redox kinetics but also aid charge separation in the absorber. Voltages of +0.4 V, +0.6 V, and +1.2 V are found for hole injection into KI, K4[Fe(CN)6], and methanol, respectively, and a voltage of −0.7 V for electron injection into K3[Fe(CN)6]. These voltages correlate well with the photocatalytic performance of the catalyst; they are influenced by the built-in potentials of the donor-acceptor configurations, the physical separation of donors and acceptors, and the reversibility of the redox reaction. The Photovoltage data also allowed the identification of a photosynthetic system for hydrogen evolution (80 μmol g−1 h−1) under visible light illumination (>400 nm) from 0.05 M aqueous K4[Fe(CN)6].
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photochemical charge separation in nanocrystal photocatalyst films insights from surface Photovoltage spectroscopy
Journal of Physical Chemistry Letters, 2014Co-Authors: Jing Zhao, Frank E OsterlohAbstract:Photochemical charge generation, separation, and transport at nanocrystal interfaces are central to photoelectrochemical water splitting, a pathway to hydrogen from solar energy. Here, we use surface Photovoltage spectroscopy to probe these processes in nanocrystal films of HCa2Nb3O10, a proven photocatalyst. Charge injection from the nanoparticles into the gold support can be observed, as well as oxidation and reduction of methanol and oxygen adsorbates on the nanosheet films. The measured Photovoltage depends on the illumination intensity and substrate material, and it varies with illumination time and with film thickness. The proposed model predicts that the Photovoltage is limited by the built-in potential of the nanosheet–metal junction, that is, the difference of Fermi energies in the two materials. The ability to measure and understand these light-induced charge separation processes in easy-to-fabricate films will promote the development of nanocrystal applications in photoelectrochemical cells, ph...
Dejun Wang - One of the best experts on this subject based on the ideXlab platform.
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a comparative study on plate like and flower like zno nanocrystals surface Photovoltage property and photocatalytic activity
Materials Chemistry and Physics, 2011Co-Authors: Lingling Wang, Dejun Wang, Tengfeng Xie, Liping Chen, Yanhong LinAbstract:Abstract ZnO nanostructures materials with two-dimensional (2D) plate-like and three-dimensional (3D) flower-like morphologies have been synthesized via facile hydrothermal process. Scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD) have been used to characterize the samples. We have compared the surface photoelectric properties of flower-like ZnO with that of plate-like ZnO by means of surface Photovoltage (SPV), field-induced surface Photovoltage (FISPV), transient Photovoltage (TPV) and surface photocurrent (SPC) techniques. Based on the Photovoltage responses, the influence of the morphology on transfer characteristics of photogenerated charge carriers was discussed. The synthesized flower-like ZnO exhibited more efficient separation and transfer properties of photogenerated charge carriers than that of plate-like ZnO in the UV region due to the special flower-like hierarchical nanostructures. We have also evaluated the photocatalytic activity of the ZnO samples by photodegradation efficiency of RhB. The experiments demonstrated that RhB in aqueous solution was more efficiently photodegraded using flower-like ZnO than plate-like ZnO. The results also show the consistency between the carrier dynamics of photogenerated electron–hole pairs and photocatalytic activity.
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surface Photovoltage characterization of a zno nanowire array cds quantum dot heterogeneous film and its application for photovoltaic devices
Nanotechnology, 2009Co-Authors: Yu Zhang, Tengfeng Xie, Tengfei Jiang, Xiao Wei, Shan Pang, Xi Wang, Dejun WangAbstract:ZnO nanowire (NWs) arrays coated with CdS quantum dots (QDs) were successfully fabricated with a chemical bath deposition process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD) have been utilized to characterize the samples. We have studied the processes of separation and recombination of the photo-generated charges in the visible region by surface Photovoltage (SPV) and transient Photovoltage (TPV) measurements. By controlling the amount of attached CdS QDs we found that the surface Photovoltage characteristics change significantly. With a liquid electrolyte as the hole transport medium, the quantum dot sensitized nanowire solar cells (QDSSCs) exhibited short-circuit currents ranging from 0.8 to 2.6 mA cm−2 and open-circuit voltages of 0.35–0.44 V when illuminated with light intensity 100 mW cm−2. The relation between the performance of QDSSCs and their Photovoltage characterization was also discussed.
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a study of the dynamic properties of photo induced charge carriers at nanoporous tio 2 conductive substrate interfaces by the transient Photovoltage technique
Nanotechnology, 2008Co-Authors: Xiao Wei, Qidong Zhao, Tengfeng Xie, Shan Pang, Dejun WangAbstract:Two interfaces with opposite orientations of the built-in electric field, nanoporous TiO2 film/ FTO electrode and nanoporous TiO2 film/semitransparent Pt substrate, were constructed. The separation and transport of photo-induced charge carriers in the two systems of nanoporous TiO2/conductive substrate were studied by the transient Photovoltage technique. Various transient Photovoltage responses were obtained when the laser beam was incident from the surface of the nanoporous TiO2 film (top illumination) or the TiO2/substrate interface (bottom illumination). A linear and a logarithmic dependence of the Photovoltage amplitude on the excitation level were observed for top illumination and bottom illumination, respectively. The results indicate that diffusion is the major way for the separation of charge carriers in the nanoporous TiO2 film and that the excess carriers were separated by drift under the built-in electric field at the TiO2/substrate interfaces.
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surface Photovoltage characterization of an oriented α fe2o3 nanorod array
Chemical Physics Letters, 2008Co-Authors: Linlin Peng, Qidong Zhao, Dejun Wang, Tengfeng Xie, Zhiyong Fan, Dan ZhengAbstract:Abstract A large aligned nanorod array of α-Fe2O3 grown on FTO substrate was prepared via a simple hydrothermal synthesis method. The photoelectric property of the array was studied by surface Photovoltage technique. Based on the Photovoltage responses on spectrum, we discussed the transfer characteristics of the photogenerated charge at the surface of the nanorods and the interface between the nanorods and the FTO substrate. The contributions of surface states and built-in electric field were discriminated. Moreover, the quantum size effect on the Photovoltage spectra could be observed only when the array was illuminated from the free surface of the nanorods.
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surface Photovoltage study of photogenerated charges in zno nanorods array grown on ito
Chemical Physics Letters, 2007Co-Authors: Qidong Zhao, Dejun Wang, Min Yang, Linlin Peng, Yanhong Lin, Tengfeng XieAbstract:A well-aligned nanorods array of ZnO was chemically grown on conductive ITO substrate at low temperature. The photogenerated charges at surface and interface were examined by surface Photovoltage techniques based on both Kelvin probe and lock-in amplifier with dc bias. The Photovoltage response bands related to band-to-band transition and bound excitons were discriminated. We demonstrated the spectrum-dependent transfer characteristic of photogenerated charges at the surface of ZnO nanorods array and the interface between ZnO and ITO.
Tengfeng Xie - One of the best experts on this subject based on the ideXlab platform.
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a comparative study on plate like and flower like zno nanocrystals surface Photovoltage property and photocatalytic activity
Materials Chemistry and Physics, 2011Co-Authors: Lingling Wang, Dejun Wang, Tengfeng Xie, Liping Chen, Yanhong LinAbstract:Abstract ZnO nanostructures materials with two-dimensional (2D) plate-like and three-dimensional (3D) flower-like morphologies have been synthesized via facile hydrothermal process. Scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD) have been used to characterize the samples. We have compared the surface photoelectric properties of flower-like ZnO with that of plate-like ZnO by means of surface Photovoltage (SPV), field-induced surface Photovoltage (FISPV), transient Photovoltage (TPV) and surface photocurrent (SPC) techniques. Based on the Photovoltage responses, the influence of the morphology on transfer characteristics of photogenerated charge carriers was discussed. The synthesized flower-like ZnO exhibited more efficient separation and transfer properties of photogenerated charge carriers than that of plate-like ZnO in the UV region due to the special flower-like hierarchical nanostructures. We have also evaluated the photocatalytic activity of the ZnO samples by photodegradation efficiency of RhB. The experiments demonstrated that RhB in aqueous solution was more efficiently photodegraded using flower-like ZnO than plate-like ZnO. The results also show the consistency between the carrier dynamics of photogenerated electron–hole pairs and photocatalytic activity.
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interface junction at anatase rutile in mixed phase tio2 formation and photo generated charge carriers properties
Chemical Physics Letters, 2011Co-Authors: Xiaoru Zhang, Yanhong Lin, Zhiyong Fan, Jianfu Zhang, Tengfeng XieAbstract:Abstract Nanosized TiO 2 photocatalysts of anatase, rutile and mixed-phase were synthesized through hydrolysis method. The influence of the interface junction between anatase and rutile TiO 2 on the photo-generated charge carriers properties were studied by Kelvin probe (KP), surface Photovoltage (SPV) and transient Photovoltage (TPV) techniques. The KP results revealed that the difference of the surface work function between anatase and rutile might cause the formation of built-in field at the interface in mixed-phase TiO 2 . The role of the interface junction was further testified through the characteristics of photo-generated charge carriers by SPV and TPV.
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surface Photovoltage characterization of a zno nanowire array cds quantum dot heterogeneous film and its application for photovoltaic devices
Nanotechnology, 2009Co-Authors: Yu Zhang, Tengfeng Xie, Tengfei Jiang, Xiao Wei, Shan Pang, Xi Wang, Dejun WangAbstract:ZnO nanowire (NWs) arrays coated with CdS quantum dots (QDs) were successfully fabricated with a chemical bath deposition process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD) have been utilized to characterize the samples. We have studied the processes of separation and recombination of the photo-generated charges in the visible region by surface Photovoltage (SPV) and transient Photovoltage (TPV) measurements. By controlling the amount of attached CdS QDs we found that the surface Photovoltage characteristics change significantly. With a liquid electrolyte as the hole transport medium, the quantum dot sensitized nanowire solar cells (QDSSCs) exhibited short-circuit currents ranging from 0.8 to 2.6 mA cm−2 and open-circuit voltages of 0.35–0.44 V when illuminated with light intensity 100 mW cm−2. The relation between the performance of QDSSCs and their Photovoltage characterization was also discussed.
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a study of the dynamic properties of photo induced charge carriers at nanoporous tio 2 conductive substrate interfaces by the transient Photovoltage technique
Nanotechnology, 2008Co-Authors: Xiao Wei, Qidong Zhao, Tengfeng Xie, Shan Pang, Dejun WangAbstract:Two interfaces with opposite orientations of the built-in electric field, nanoporous TiO2 film/ FTO electrode and nanoporous TiO2 film/semitransparent Pt substrate, were constructed. The separation and transport of photo-induced charge carriers in the two systems of nanoporous TiO2/conductive substrate were studied by the transient Photovoltage technique. Various transient Photovoltage responses were obtained when the laser beam was incident from the surface of the nanoporous TiO2 film (top illumination) or the TiO2/substrate interface (bottom illumination). A linear and a logarithmic dependence of the Photovoltage amplitude on the excitation level were observed for top illumination and bottom illumination, respectively. The results indicate that diffusion is the major way for the separation of charge carriers in the nanoporous TiO2 film and that the excess carriers were separated by drift under the built-in electric field at the TiO2/substrate interfaces.
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surface Photovoltage characterization of an oriented α fe2o3 nanorod array
Chemical Physics Letters, 2008Co-Authors: Linlin Peng, Qidong Zhao, Dejun Wang, Tengfeng Xie, Zhiyong Fan, Dan ZhengAbstract:Abstract A large aligned nanorod array of α-Fe2O3 grown on FTO substrate was prepared via a simple hydrothermal synthesis method. The photoelectric property of the array was studied by surface Photovoltage technique. Based on the Photovoltage responses on spectrum, we discussed the transfer characteristics of the photogenerated charge at the surface of the nanorods and the interface between the nanorods and the FTO substrate. The contributions of surface states and built-in electric field were discriminated. Moreover, the quantum size effect on the Photovoltage spectra could be observed only when the array was illuminated from the free surface of the nanorods.
Qidong Zhao - One of the best experts on this subject based on the ideXlab platform.
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a study of the dynamic properties of photo induced charge carriers at nanoporous tio 2 conductive substrate interfaces by the transient Photovoltage technique
Nanotechnology, 2008Co-Authors: Xiao Wei, Qidong Zhao, Tengfeng Xie, Shan Pang, Dejun WangAbstract:Two interfaces with opposite orientations of the built-in electric field, nanoporous TiO2 film/ FTO electrode and nanoporous TiO2 film/semitransparent Pt substrate, were constructed. The separation and transport of photo-induced charge carriers in the two systems of nanoporous TiO2/conductive substrate were studied by the transient Photovoltage technique. Various transient Photovoltage responses were obtained when the laser beam was incident from the surface of the nanoporous TiO2 film (top illumination) or the TiO2/substrate interface (bottom illumination). A linear and a logarithmic dependence of the Photovoltage amplitude on the excitation level were observed for top illumination and bottom illumination, respectively. The results indicate that diffusion is the major way for the separation of charge carriers in the nanoporous TiO2 film and that the excess carriers were separated by drift under the built-in electric field at the TiO2/substrate interfaces.
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surface Photovoltage characterization of an oriented α fe2o3 nanorod array
Chemical Physics Letters, 2008Co-Authors: Linlin Peng, Qidong Zhao, Dejun Wang, Tengfeng Xie, Zhiyong Fan, Dan ZhengAbstract:Abstract A large aligned nanorod array of α-Fe2O3 grown on FTO substrate was prepared via a simple hydrothermal synthesis method. The photoelectric property of the array was studied by surface Photovoltage technique. Based on the Photovoltage responses on spectrum, we discussed the transfer characteristics of the photogenerated charge at the surface of the nanorods and the interface between the nanorods and the FTO substrate. The contributions of surface states and built-in electric field were discriminated. Moreover, the quantum size effect on the Photovoltage spectra could be observed only when the array was illuminated from the free surface of the nanorods.
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surface Photovoltage study of photogenerated charges in zno nanorods array grown on ito
Chemical Physics Letters, 2007Co-Authors: Qidong Zhao, Dejun Wang, Min Yang, Linlin Peng, Yanhong Lin, Tengfeng XieAbstract:A well-aligned nanorods array of ZnO was chemically grown on conductive ITO substrate at low temperature. The photogenerated charges at surface and interface were examined by surface Photovoltage techniques based on both Kelvin probe and lock-in amplifier with dc bias. The Photovoltage response bands related to band-to-band transition and bound excitons were discriminated. We demonstrated the spectrum-dependent transfer characteristic of photogenerated charges at the surface of ZnO nanorods array and the interface between ZnO and ITO.
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influence of adsorbed oxygen on the surface Photovoltage and photoluminescence of zno nanorods
Nanotechnology, 2006Co-Authors: Dejun Wang, Ziheng Li, Qidong Zhao, Min YangAbstract:ZnO nanorods have been prepared with sol–gel methods using zinc acetate dihydrate in ethanol in the presence of lithium hydroxide via alkaline hydrolysis. The electron transfer behaviour at the surface and interface in ZnO nanorods was investigated by means of the surface Photovoltage technique. The influence of adsorbed oxygen on the surface Photovoltage (SPV) response of ZnO nanorods was studied by surface Photovoltage spectroscopy (SPS) and field-induced surface Photovoltage spectroscopy (FISPS). The results of SPS demonstrate that for ZnO nanorods the built-in electric field should be a main driving force for the separation of the photogenerated electron–hole pairs and its ensuing SPV response. The method of photogenerated charge recombination was also studied with the aid of PL spectroscopy. It is shown that the two methods of energy relaxation in light-excited ZnO nanorods are competitive. When oxygen is adsorbed at the surface and the built-in electric field is formed, the SPV response should be the leading one. Nevertheless, when oxygen is absent, the energy relaxation is mostly carried out by radiative emission.
Michael Gratzel - One of the best experts on this subject based on the ideXlab platform.
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elucidation of Photovoltage origin and charge transport in cu2o heterojunctions for solar energy conversion
Sustainable Energy and Fuels, 2019Co-Authors: Matthew T Mayer, Peter Cendula, Jingshan Luo, Michael GratzelAbstract:Heterojunctions between p-type cuprous oxide (Cu2O) and suitable n-type layers stand out as some of the best performing and abundant oxide photoabsorbers currently available for the generation of hydrogen with photoelectrochemical cells or conversion of solar energy to electricity. In this contribution, we used drift-diffusion semiconductor modeling to investigate the mechanism governing the charge transport in TiO2/Ga2O3/Cu2O and TiO2/Al:ZnO/Cu2O heterojunctions. The simulated Photovoltage 0.9 V for TiO2/Ga2O3/Cu2O agrees well with the measured value of 1.0 V and the governing mechanism is identified to be thermionic emission of electrons across the Ga2O3/TiO2 interface. By modeling an optimized increase in Ga2O3 donor concentration, a Photovoltage improvement of only 0.1 V is achievable, whereas further optimizing the electron affinity of Ga2O3 may lead to more significant improvement approaching 0.7 V. The optimized electron affinity of Ga2O3 enabled a simulated Photovoltage of 1.6 V, close to the theoretical limit for Cu2O with a 2.17 eV bandgap energy. Additionally, we find that simulations can reproduce the measured Photovoltage of TiO2/Al:ZnO/Cu2O only when an interface recombination layer at the Al:ZnO/Cu2O interface is included in the model. Our findings enable detailed understanding of the charge transport mechanism in Cu2O heterojunctions and offer various design directions for further Photovoltage improvement.
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function follows form correlation between the growth and local emission of perovskite structures and the performance of solar cells
Advanced Functional Materials, 2017Co-Authors: Ibrahim M Dar, Shaik M Zakeeruddin, Alexander Hinderhofer, G Jacopin, Valentina Belova, Neha Arora, Frank Schreiber, Michael GratzelAbstract:Understanding the relationship between the growth and local emission of hybrid perovskite structures and the performance of the devices based on them demands attention. This study investigates the local structural and emission features of CH3NH3PbI3, CH3NH3PbBr3, and CH(NH2)2PbBr3 perovskite films deposited under different yet optimized conditions using X-ray scattering and cathodoluminescence spectroscopy, respectively. X-ray scattering shows that a CH3NH3PbI3 film involving spin coating of CH3NH3I instead of dipping is composed of perovskite structures exhibiting a preferred orientation with [202] direction perpendicular to the surface plane. The device based on the CH3NH3PbI3 film composed of oriented crystals yields a relatively higher Photovoltage. In the case of CH3NH3PbBr3, while the crystallinity decreases when the HBr solution is used in a single-step method, the Photovoltage enhancement from 1.1 to 1.46 V seems largely stemming from the morphological improvements, i.e., a better connection between the crystallites due to a higher nucleation density. Furthermore, a high Photovoltage of 1.47 V obtained from CH(NH2)2PbBr3 devices could be attributed to the formation of perovskite films displaying uniform cathodoluminescence emission. The comparative analysis of the local structural, morphological, and emission characteristics of the different perovskite films supports the higher Photovoltage yielded by the relatively better performing devices.
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intrinsic and extrinsic stability of formamidinium lead bromide perovskite solar cells yielding high Photovoltage
Nano Letters, 2016Co-Authors: Neha Arora, Norman Pellet, Fabrizio Giordano, Shaik M Zakeeruddin, G Jacopin, Mojtaba Abdijalebi, Richard H Friend, Michael GratzelAbstract:We report on both the intrinsic and the extrinsic stability of a formamidinium lead bromide [CH(NH2)2PbBr3 = FAPbBr3] perovskite solar cell that yields a high Photovoltage. The fabrication of FAPbBr3 devices, displaying an outstanding Photovoltage of 1.53 V and a power conversion efficiency of over 8%, was realized by modifying the mesoporous TiO2–FAPbBr3 interface using lithium treatment. Reasons for improved photovoltaic performance were revealed by a combination of techniques, including photothermal deflection absorption spectroscopy (PDS), transient-Photovoltage and charge-extraction analysis, and time-integrated and time-resolved photoluminescence. With lithium-treated TiO2 films, PDS reveals that the TiO2–FAPbBr3 interface exhibits low energetic disorder, and the emission dynamics showed that electron injection from the conduction band of FAPbBr3 into that of mesoporous TiO2 is faster than for the untreated scaffold. Moreover, compared to the device with pristine TiO2, the charge carrier recombinati...
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perovskite hematite tandem cells for efficient overall solar driven water splitting
Nano Letters, 2015Co-Authors: Dharani Sabba, Mulmudi Hemant Kumar, Lydia Helena Wong, James Barber, Michael Gratzel, Nripan MathewsAbstract:Photoelectrochemical water splitting half reactions on semiconducting photoelectrodes have received much attention but efficient overall water splitting driven by a single photoelectrode has remained elusive due to stringent electronic and thermodynamic property requirements. Utilizing a tandem configuration wherein the total Photovoltage is generated by complementary optical absorption across different semiconducting electrodes is a possible pathway to unassisted overall light-induced water splitting. Because of the low Photovoltages generated by conventional photovoltaic materials (e.g., Si, CIGS), such systems typically consist of triple junction design that increases the complexity due to optoelectrical trade-offs and are also not cost-effective. Here, we show that a single solution processed organic–inorganic halide perovskite (CH3NH3PbI3) solar cell in tandem with a Fe2O3 photoanode can achieve overall unassisted water splitting with a solar-to-hydrogen conversion efficiency of 2.4%. Systematic elec...
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high efficiency dye sensitized solar cell with three dimensional photoanode
Nano Letters, 2011Co-Authors: Nicolas Tetreault, Shaik M Zakeeruddin, Eric Arsenault, Leophilipp Heiniger, Navid Soheilnia, Jeremie Brillet, Thomas Moehl, Geoffrey A Ozin, Michael GratzelAbstract:Herein, we present a straightforward bottom-up synthesis of a high electron mobility and highly light scattering macroporous photoanode for dye-sensitized solar cells. The dense three-dimensional Al/ZnO, SnO2, or TiO2 host integrates a conformal passivation thin film to reduce recombination and a large surface-area mesoporous anatase guest for high dye loading. This novel photoanode is designed to improve the charge extraction resulting in higher fill factor and Photovoltage for DSCs. An increase in Photovoltage of up to 110 mV over state-of-the-art DSC is demonstrated.