Combining near-coincidence-site lattice (NCSL) calculations and fringing-field simulations, we investigate the formation conditions and spatial vector distribution of the interfacial electric field at anatase/rutile phase junctions in TiO2 nanoparticles. Our analysis reveals that charge separation in these mixed-phase systems is governed not by the long-range built-in field of a classical depletion region, but by a strong, short-range fringing field localized at the phase boundary. The minority-carrier migration length defines an optimal phase-size combination of approximately 20 nm anatase and 6-13 nm rutile, within which the fringing-field strength exceeds 102 kV·cm-1. This work provides a quantitative design principle for enhancing charge separation efficiency through precise nanoscale phase engineering in mixed-phase photocatalysts and photovoltaic devices.

This review examines nickel oxide (NiO x ) as a stable p-type hole injection/transport material for QLEDs, summarizing advances in synthesis, optimization, and device integration that enable the development of efficient, commercial QLEDs.

The poor efficiency and stability of blue Quantum Dot Light-Emitting diodes (QLED) hinders the practical applications of QLEDs full-color displays. Excessive electron injection, insufficient hole injection, and abundant defects on the surface of quantum dots (QD) are the main issues limiting the performance of blue devices. Herein, an in situ treatment with bipolar small molecule polydentate ligand-guanidine chloride (GACl) is proposed to simultaneously suppress excessive electron injection, patch surface defects of QDs and enhance hole injection. GACl-treated blue QLEDs exhibited a remarkable increase in maximal external quantum Efficiency (EQE) from 16.3% to a record 23.5%, accompanied by maximal luminance (36810 cd m-2), excellent maximal current efficiency (17.5 cd A-1), and enhanced device stability. Combining C-V and J-V characteristics, a concise physical model of hole injection is also established: Below 3 V, hole injection is controlled by the interfacial barrier, primarily through tunneling and thermionic injection; Above 3 V, the interfacial barrier is eliminated, and hole injection efficiency is governed by transport within the QD layer. This study showed a clear physical model for understanding the hole injection mechanism in QLEDs, offering valuable design strategies for improving the performance of blue-QLEDs.

Fabrication of a large-scale, high-performance, high stability cylinder freestanding rotating triboelectric nanogenerator (FR-TENG) for mechanical -energy -driven CO 2 reduction is a bottleneck to be overcome. Herein, from the reasonable geometric structure and triboelectric materials, a cylinder -type, large -area, high -stability, and soft -contact FR-TENG with superior output performance was well -constructed. At the optimal conditions, the maximum short-circuit current of FR-TENG is 35.1 mu A, the maximum transferred triboelectric charge is 350 nC, and the conversion efficiency from mechanical to electrical energy is up to 16.7 %, which outperforms previously reported results under similar conditions. Applying it into triboelectric plasma reduction of CO 2 system, the evolution rates of CO and O 2 are 8.50 and 4.33 mu mol h -1 , respectively, and the conversion efficiency from mechanical to chemical energy is 1.84 %, which is better than most of the previous benchmark results in TENG driven-CO 2 reduction systems. Finally, this device is applied to field experiments, and the generation rates of CO and O 2 are obtained to be 5.06 and 2.33 mu mol h -1 at a wind speed of 2.3 m s - 1 , respectively, with a maximum energy conversion efficiency of 0.72 %. This work provides a promising strategy for CO 2 reduction systems driven by mechanical energy.

The water-splitting reaction using photocatalyst particles is a promising route for solar fuel production1-4. Photo-induced charge transfer from a photocatalyst to catalytic surface sites is key in ensuring photocatalytic efficiency5; however, it is challenging to understand this process, which spans a wide spatiotemporal range from nanometres to micrometres and from femtoseconds to seconds6-8. Although the steady-state charge distribution on single photocatalyst particles has been mapped by microscopic techniques9-11, and the charge transfer dynamics in photocatalyst aggregations have been revealed by time-resolved spectroscopy12,13, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and their exact mechanism is unknown. Here we perform spatiotemporally resolved surface photovoltage measurements on cuprous oxide photocatalyst particles to map holistic charge transfer processes on the femtosecond to second timescale at the single-particle level. We find that photogenerated electrons are transferred to the catalytic surface quasi-ballistically through inter-facet hot electron transfer on a subpicosecond timescale, whereas photogenerated holes are transferred to a spatially separated surface and stabilized through selective trapping on a microsecond timescale. We demonstrate that these ultrafast-hot-electron-transfer and anisotropic-trapping regimes, which challenge the classical perception of a drift-diffusion model, contribute to the efficient charge separation in photocatalysis and improve photocatalytic performance. We anticipate that our findings will be used to illustrate the universality of other photoelectronic devices and facilitate the rational design of photocatalysts.

Ferrihydrite (Fh) has been demonstrated acting as a hole-storage layer (HSL) in photoelectrocatalysis system. However, the intrinsic structure responsible for the hole storage function for Fh remains unclear. Herein, by dehydrating the Fh via a careful calcination, the essential relation between the HSL function and the structure evolution of Fh material is unraveled. The irreversible and gradual loss of crystal water molecules in Fh leads to the weakening of the HSL function, accompanied with the arrangement of inner structure units. A structure evolution of the dehydration process is proposed and the primary active structure of Fh for HSL is identified as the [FeO6] polyhedral units bonding with two or three molecules of crystal water. With the successive loss of chemical crystal water, the coordination symmetry of [FeO6] hydration units undergoes mutation and a more ordered structure is formed, causing the difficulty for accepting photogenerated holes as a consequence.

Hole transport layers (HTLs) in perovskite photovoltaics do not just play a key role in device performance; they also determine the overall flexibility, cost, and opportune tandem solar cell applications. Currently used HTLs have limited functionality and are costly. Here, we develop an efficient bifunctional and cost-effective HTL based on electrochemically deposited polyaniline (PAN) decorated with dodecyl benzene sulfonic acid. We then resurface PAN with chlorine to improve HTL conductivity and to provide nucleation sites for the growth and passivation of perovskite films. The synergetic modification on the perovskite/PAN interface and crystallographic/optoelectric properties of the perovskite film delivers a photovoltaic efficiency of 20.7% for a small-area inverted cell, the highest among any polyaniline-based perovskite solar cells. An efficiency of 18.4% is achieved for 1 cm2 devices. This work provides a competitive category of in situ passivasive HTLs for efficient and scalable perovskite solar cells.

The cocatalysts or dual cocatalysts of photocatalysts are indispensable for high efficiency in artificial photosynthesis for solar fuel production. However, the reaction activity increased by cocatalysts cannot be directly ascribed to the accelerated catalytic kinetics, since photogenerated charges are involved in the elementary steps of photocatalytic reactions. To date, diverging views about cocatalysts show that their exact role for photocatalysis is not well understood yet. Herein, we image directly the local separation of photogenerated charge carriers across single crystals of the BiVO4 photocatalyst which loaded locally with nanoparticles of a MnOx single cocatalyst or with nanoparticles of a spatially separated MnOx and Pt dual cocatalyst. The deposition of the single cocatalyst resulted not only in a strong increase of the interfacial charge transfer but also, surprisingly, in a change of the direction of built-in electric fields beneath the uncovered surface of the photocatalyst. The additive electric fields caused a strong increase of local surface photovoltage signals (up to 80 times) and correlated with the increase of the photocatalytic performance. The local electric fields were further increased (up to 2.5 kV·cm-1) by a synergetic effect of the spatially separated dual cocatalysts. The results reveal that cocatalyst has a conclusive effect on charge separation in photocatalyst particle by aligning the vectors of built-in electric fields in the photocatalyst particle. This effect is beyond its catalytic function in thermal catalysis.

Defects can markedly impact the performance of semiconductor-based photocatalysts, where the spatial separation of photogenerated charges is required for converting solar energy into fuels. However, understanding exactly how defects affect photogenerated charge separation at nanometer scale remains quite challenging. Here, using time- and space-resolved surface photovoltage approaches, we demonstrate that the distribution of surface photogenerated charges and the direction of photogenerated charge separation are determined by the defects distributed within a 100 nm surface region of a photocatalytic Cu2O particle. This is enabled by the defect-induced charge separation process, arising from the trapping of electrons at the near-surface defect states and the accumulation of holes at the surface states. More importantly, the driving force for defect-induced charge separation is greater than 4.2 kV/cm and can be used to drive photocatalytic reactions. These findings highlight the importance of near-surface defect engineering in promoting photogenerated charge separation and manipulating surface photogenerated charges; further, they open up a powerful avenue for improving photocatalytic charge separation and solar energy conversion efficiency.

Solar-driven photocatalytic reactions provide a potential route to sustainable fuels. These processes rely on the effective separation of photogenerated charges, and therefore understanding and exploring the driving force for charge separation is key to improving the photocatalytic performance. Here, using surface photovoltage microscopy, we demonstrate that the photogenerated charges can be separated effectively in a high-symmetry Cu2O photocatalyst particle by asymmetric light irradiation. The holes and electrons are transferred to the illuminated and shadow regions, respectively, of a single photocatalytic particle. Quantitative results show that the intrinsic difference between electron and hole mobilities enables a diffusion-controlled charge separation process, which is stronger than that caused by conventional built-in electric fields (40 mV versus 10 mV). Based on the findings, we assemble spatially separated redox co-catalysts on a single photocatalytic particle and, in doing so, enhance the performance for a model photocatalytic reaction by 300%. These findings highlight the driving force caused by charge mobility differences and the use of asymmetric light illumination for charge separation in photocatalysis.

To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady-state analyses as well as ultra-fast photoluminescence and photovoltage decays. Thus this paper provides a good buffer layer to the community of quantum dot solar cells.

A larger value (0.86 V) of open-circuit photovoltage (Voc) of the TiO2 nanotube (NT)-based dye sensitised solar cells (DSSCs) than that of DSSCs constructed from TiO2 nanoparticles (NPs) has been observed. Work function of TiO2 NTs is about 0.3 eV less than that of TiO2 NPs, which indicates that the conduction band in TiO2 NTs may has a more negative shift in comparison with that of TiO2 NPs after TiO2 contacts with oxidative electrolyte. This may be one origin of Voc enhancement. Moreover, comparative analyses on surface photovoltage and transient photovoltage of TiO2 NPs and NTs show that the larger built-in field in the interface between TiO2 NTs and Ti foil can further improve charge separation and transport in the TiO2 NT film, which will result in recombination decrement and charge lifetime increment. This may be the other origin of Voc enhancement.

The photoexcited electrons transfer dynamics of the CdS quantum dots (QDs) deposited in TiO2 nanowire array films are studied using surface photovoltage (SPV) and transient photovoltage (TPV) techniques. By comparing the SPV results with different thicknesses of QDs layers, we can separate the dynamic characteristics of photoexcited electrons injection and trapping. It is found that the TPV signals of photoexcited electrons trapped in the CdS QDs occur at timescales of about 2 x 10(-8) s, which is faster than that of the photoexcited electrons injected from CdS into TiO2. More than 90 nm of the thickness of the CdS QDs layer will seriously affect the photoexcited electrons transfer and injection. (C) 2014 AIP Publishing LLC.

Cu(In1-x,Ga-x)Se-2 (CIGS) films were prepared by one-step electrodeposition method on FTO glass substrates, and the influence of electrolytic pH on the chemical composition, structure and photovoltaic performance of CIGS thin-films were studied in detail. The results showed that the stoichiometry of In and Ga in the film could be effectively regulated by changing the pH value of the electrolyte. The X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) results showed that the CIGS thin-films had good crystallinity and uniform particle size distribution when the pH value was 2.0. The effect of different stoichiometries of the CIGS thin-films on the kinetics of photo-charges was also studied. The CIGS thin film with a stoichiometric ratio of 0.3 for Ga/(In + Ga) presented the strongest surface photovoltaic effect.

The dynamic photo induced charge separation and transport properties of pulsed-magnetron-sputtered TiO2, WO3, and WO3-TiO2 double-layer films were investigated using the transient photovoltage (TPV) technique. Effective charge separation and transport were observed for the WO3-TiO2 heterojunction, which was about three times larger than those of the TiO2 and WO3 single-layer films. The TPV response of the WO3-TiO2 heterojunction peaked at 28 ns with a recombination lifetime of 179 ns. These results suggested that the electron injection from TiO2 under illumination was the dominant factor for the separation of photo induced charge carriers in the WO3-TiO2 double-layer films. (C) 2012 The Japan Society of Applied Physics

Single crystal TiO2 nanorod arrays grown on FTO substrate were prepared by hydrothermal method. The morphology, structure and photoelectric property were investigated with scanning electron microscope (SEM), X-ray diffraction spectrum (XRD), ultraviolet-visible absorption spectrum (UV-Vis) and surface photovoltage spectrum(SPS), respectively. In the contraction of different arrays with different substrates we found that the FTO substrate had a decisive effect on the growth of nanorod arrays. The lattices of TiO2 seed layer and SnO2: F matched very well, which helped the epitaxial growth and the orientation of nanorod arrays. According to the field induced surface photovoltage spectroscopy, there was a band upward bending in TiO2 nanorods at the interface of TiO2 and FTO. Introducing seed layer into the process of growth can help the orientation of array, decrease the interface state greatly and provide the potential to increase the collection efficiency of carrier.

In this paper, CuInSe2 thin films were prepared by one-step potentiostatic electrodeposition method on the indium tin oxide (ITO) substrates, we researched the effect of the different deposition concentration ratio and pH values on the structural performance of CuInSe2 thin films in the process. The surface morphology, stoichiometric ratio and crystal structure were characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) respectively. The results showed that pH value have a significant impact on the surface morphology,chemical composition,crystal structure of these thin films, high-quality thin films with indium-rich or copper-rich have been prepared by controlling the appropriate concentration and acidity. We researched the opto-electrical separation properties of Cu-rich and in-rich CuInSe2 thin films by the surface photovoltage spectroscopy (SPS), the results showed that indium-rich film has a strong opto-electrical response;Due to the Cu-Se phase exist in these copper-rich films, which form a new interface in the films, electron-hole pairs recombine at the interface owing to the capture, result in a strong depression of opto-electrical response.

The thin copper films were deposited by magnet sputtering on fluorine-doped tin oxide (FTO) coated glass. The CuO nanowires array film can be obtained through the heat oxidation process. The morphology and microstructure of the copper film and the CuO nanowires film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), respectively. The CO and H 2 S sensing characteristics of the CuO nanowires array film were also investigated. The results show that CuO nanowires array film exhibited highest response to CO gas at 250°C. The response was significantly enhanced when the CO gas concentration was increased. There is a sensing response at low gas concentration for H 2 S at room temperature. While for the higher temperature, the resistance of the CuO nanowires array film decreased rapidly, which is different from the CO gas. The abnormal resistance change for the H 2 S was also illustrated in this article.

Well-aligned CdS/TiO2 nanotube array composite film was fabricated on the indium-doped tin oxide(ITO) substrate by templating ZnO nanorod array film.The effects of CdS deposition time on the morphology,crystal structure,photo-electric properties of TiO2/CdS composite film were investigated via scanning electron microscopy(SEM),X-ray diffraction(XRD),ultraviolet-visible absorption spectrum(UV-Vis) and surface photovoltage spectrum(SPS).The results showed that the absorbance of composite film extended to the visible region compared with the pristine TiO2 nanotube arrays.The SPS also showed a new response region relative to the absorption spectrum.This result indicated a remarkable photo-electric conversion efficiency improvement in the visible region.We also found that the SPS response intensity of composite film decreased gradually in the visible region with the increase of CdS deposition time.We interpreted and discussed this phenomenon using distinct photo-induced charge generation and transfer mechanisms detailedly.Despite this,we also discussed the influence of surface-to-volume ratio on the final photo-electric properties for the CdS/TiO2 nanotube array composite film.

Well-aligned ZnO/CdS composite nanorod array film was grown on an indium tin oxide (ITO) substrate by two-step chemical solution deposition method. The effects of CdS deposition time on the crystal structure, morphology, and photoelectric performance of the ZnO/CdS composite film were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet. visible absorption spectroscopy (UV-Vis), photoluminescence spectroscopy (PL), and surface photovoltage spectroscopy (SPS). Results showed that the absorbance of the composite film extended into the visible region compared with the bare ZnO nanorod arrays. SPS also showed a new response region corresponding to the absorption spectrum. This result indicated a remarkable photoelectric conversion efficiency improvement in the visible region. We also found that the SPS response intensity of the composite film decreased gradually above 383 nm with an increase in CdS deposition time. However, the SPS response intensity increased below 383 nm. We interpreted this phenomenon using two distinct photoinduced charge generation and transfer mechanisms.