1
|
Surface-Mediated Charge Transfer of Photogenerated Carriers in Diamond. SMALL METHODS 2023; 7:e2300423. [PMID: 37596059 DOI: 10.1002/smtd.202300423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 06/20/2023] [Indexed: 08/20/2023]
Abstract
Solvated electrons are highly reductive chemical species whose chemical properties remain largely unknown. Diamond materials are proposed as a promising emitter of solvated electrons and visible light excitation would enable solar-driven CO2 or N2 reductions reactions in aqueous medium. But sub-bandgap excitation remains challenging. In this work, the role of surface states on diamond materials for charge separation and emission in both gaseous and aqueous environments from deep UV to visible light excitation is elucidated. Four different X-ray and UV-vis spectroscopy methods are applied to diamond materials with different surface termination, doping and crystallinity. Surface states are found to dominate sub-bandgap charge transfer. However, the surface charge separation is drastically reduced for boron-doped diamond due to a very high density of bulk defects. In a gaseous atmosphere, the oxidized diamond surface maintains a negative electron affinity, allowing charge emission, due to remaining hydrogenated and hydroxylated groups. In an aqueous electrolyte, a photocurrent for illumination down to 3.5 eV is observed for boron-doped nanostructured diamond, independent of the surface termination. This study opens new perspectives on photo-induced interfacial charge transfer processes from metal-free semiconductors such as diamonds.
Collapse
|
2
|
Spatiotemporal imaging of charge transfer in photocatalyst particles. Nature 2022; 610:296-301. [PMID: 36224420 DOI: 10.1038/s41586-022-05183-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Accepted: 08/02/2022] [Indexed: 11/09/2022]
Abstract
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.
Collapse
|
3
|
Synthesis Control of Charge Separation at Anatase TiO 2 Thin Films Studied by Transient Surface Photovoltage Spectroscopy. ACS APPLIED MATERIALS & INTERFACES 2022; 14:43163-43170. [PMID: 36100206 PMCID: PMC9523608 DOI: 10.1021/acsami.2c09032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Accepted: 09/02/2022] [Indexed: 06/15/2023]
Abstract
For the efficient photocatalytic oxidation of organic pollutants at surfaces of semiconductors, photogenerated holes shall be separated toward the surface and transferred to reactive surface sites, whereas the transfer of photogenerated electrons toward the surface shall be minimized. In this Research Article, the identification of suitable synthesis control of charge separation combined with an in-depth understanding of charge kinetics and trapping passivation mechanisms at the related surfaces can provide tremendous opportunities for boosting the photocatalytic performance. In this work, a comprehensive transient surface photovoltage spectroscopy study of charge separation at anatase TiO2 thin films, synthesized by ultrasonic spray pyrolysis from titanium(IV) isopropoxide (TTIP)-acetylacetone (AcacH) based precursor is reported. By varying the amount of AcacH in the precursor solution, an experimental approach of synthesis control of the charge transfer toward TiO2 surface is provided for the first time. An increased amount of AcacH in the precursor promotes transition from preferential fast electron to preferential fast hole transfer toward anatase surface, correlating with a strong increase of the photocatalytic decomposition rate of organic pollutants. Suitable mechanisms of AcacH-induced passivation of electron traps at TiO2 surfaces are analyzed, providing a new degree of freedom for tailoring the properties of photocatalytic systems.
Collapse
|
4
|
Electrochemical formation of photoactive organic heterojunctions. Porphyrin-C60 polymeric photoelectrochemical cells. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2020.137333] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
5
|
Correction to Perfluorinated Self-Assembled Monolayers Enhance the Stability and Efficiency of Inverted Perovskite Solar Cells. ACS NANO 2020; 14:16156. [PMID: 33166445 DOI: 10.1021/acsnano.0c08081] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
|
6
|
Correction to Visualizing the Nano Cocatalyst Aligned Electric Fields on Single Photocatalyst Particles. NANO LETTERS 2020; 20:8426. [PMID: 33119323 DOI: 10.1021/acs.nanolett.0c04194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
|
7
|
Toppling Pencils-Macroscopic Randomness from Microscopic Fluctuations. ENTROPY (BASEL, SWITZERLAND) 2020; 22:E1046. [PMID: 33286814 PMCID: PMC7597105 DOI: 10.3390/e22091046] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Revised: 09/15/2020] [Accepted: 09/16/2020] [Indexed: 12/13/2022]
Abstract
We construct a microscopic model to study discrete randomness in bistable systems coupled to an environment comprising many degrees of freedom. A quartic double well is bilinearly coupled to a finite number N of harmonic oscillators. Solving the time-reversal invariant Hamiltonian equations of motion numerically, we show that for N=1, the system exhibits a transition with increasing coupling strength from integrable to chaotic motion, following the Kolmogorov-Arnol'd-Moser (KAM) scenario. Raising N to values of the order of 10 and higher, the dynamics crosses over to a quasi-relaxation, approaching either one of the stable equilibria at the two minima of the potential. We corroborate the irreversibility of this relaxation on other characteristic timescales of the system by recording the time dependences of autocorrelation, partial entropy, and the frequency of jumps between the wells as functions of N and other parameters. Preparing the central system in the unstable equilibrium at the top of the barrier and the bath in a random initial state drawn from a Gaussian distribution, symmetric under spatial reflection, we demonstrate that the decision whether to relax into the left or the right well is determined reproducibly by residual asymmetries in the initial positions and momenta of the bath oscillators. This result reconciles the randomness and spontaneous symmetry breaking of the asymptotic state with the conservation of entropy under canonical transformations and the manifest symmetry of potential and initial condition of the bistable system.
Collapse
|
8
|
Revealing the relationship between photoelectrochemical performance and interface hole trapping in CuBi 2O 4 heterojunction photoelectrodes. Chem Sci 2020; 11:11195-11204. [PMID: 34094360 PMCID: PMC8162275 DOI: 10.1039/d0sc03030a] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
p-Type CuBi2O4 is considered a promising metal oxide semiconductor for large-scale, economic solar water splitting due to the optimal band structure and low-cost fabrication. The main challenge in utilizing CuBi2O4 as a photoelectrode for water splitting, is that it must be protected from photo-corrosion in aqueous solutions, an inherent problem for Cu-based metal oxide photoelectrodes. In this work, several buffer layers (CdS, BiVO4, and Ga2O3) were tested between CuBi2O4 and conformal TiO2 as the protection layer. RuOx was used as the co-catalyst for hydrogen evolution. Factors that limit the photoelectrochemical performance of the CuBi2O4/TiO2/RuOx, CuBi2O4/CdS/TiO2/RuOx, CuBi2O4/BiVO4/TiO2/RuOx and CuBi2O4/Ga2O3/TiO2/RuOx heterojunction photoelectrodes were revealed by comparing photocurrents, band offsets, and directed charge transfer measured by modulated surface photovoltage spectroscopy. For CuBi2O4/Ga2O3/TiO2/RuOx photoelectrodes, barriers for charge transfer strongly limited the performance. In CuBi2O4/CdS/TiO2/RuOx, the absence of hole traps resulted in a relatively high photocurrent density and faradaic efficiency for hydrogen evolution despite the presence of pronounced deep defect states at the CuBi2O4/CdS interface. Hole trapping limited the performance moderately in CuBi2O4/BiVO4/TiO2/RuOx and strongly in CuBi2O4/TiO2/RuOx photoelectrodes. For the first time, our results show that hole trapping is a key factor that must be addressed to optimize the performance of CuBi2O4-based heterojunction photoelectrodes. CdS, BiVO4, and Ga2O3 buffer layers were tested between CuBi2O4 and TiO2 in heterojunction photoelectrodes. Photoelectrochemical analysis and modulated surface photovoltage spectroscopy revealed that interface hole traps impacted device performance.![]()
Collapse
|
9
|
Assessment of a W:BiVO 4-CuBi 2O 4Tandem Photoelectrochemical Cell for Overall Solar Water Splitting. ACS APPLIED MATERIALS & INTERFACES 2020; 12:13959-13970. [PMID: 32096970 DOI: 10.1021/acsami.0c00696] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We assess a tandem photoelectrochemical cell consisting of a W:BiVO4 photoanode top absorber and a CuBi2O4 photocathode bottom absorber for overall solar water splitting. We show that the W:BiVO4 photoanode oxidizes water and produces oxygen at potentials ≥0.7 V vs RHE when CoPi is added as a cocatalyst. However, the CuBi2O4 photocathode does not produce a detectable amount of hydrogen from water reduction even when Pt or RuOx is added as a cocatalyst because the photocurrent primarily goes toward photocorrosion of CuBi2O4 rather than proton reduction. Protecting the CuBi2O4 photocathode with a CdS/TiO2 heterojunction and adding RuOx as a cocatalyst prevents photocorrosion and allows for photoelectrochemical production of hydrogen at potentials ≤0.3 V vs RHE. A tandem photoelectrochemical cell composed of a W:BiVO4/CoPi photoanode and a CuBi2O4/CdS/TiO2/RuOx photocathode produces hydrogen which can be detected under illumination at an applied bias of ≥0.4 V. Since the valence band of BiVO4 and conduction band of CuBi2O4 are adequately positioned to oxidize water and reduce protons, we hypothesize that the applied bias is required to overcome the relatively low photovoltages of the photoelectrodes, that is, the relatively low quasi-Fermi level splitting within BiVO4 and CuBi2O4. This work is the first experimental demonstration of hydrogen production from a BiVO4-CuBi2O4-based tandem cell and it provides important insights into the significance of photovoltage in tandem devices for overall water splitting, especially for cells containing CuBi2O4 photocathodes.
Collapse
|
10
|
Perfluorinated Self-Assembled Monolayers Enhance the Stability and Efficiency of Inverted Perovskite Solar Cells. ACS NANO 2020; 14:1445-1456. [PMID: 31909973 DOI: 10.1021/acsnano.9b03268] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Perovskite solar cells are among the most exciting photovoltaic systems as they combine low recombination losses, ease of fabrication, and high spectral tunability. The Achilles heel of this technology is the device stability due to the ionic nature of the perovskite crystal, rendering it highly hygroscopic, and the extensive diffusion of ions especially at increased temperatures. Herein, we demonstrate the application of a simple solution-processed perfluorinated self-assembled monolayer (p-SAM) that not only enhances the solar cell efficiency, but also improves the stability of the perovskite absorber and, in turn, the solar cell under increased temperature or humid conditions. The p-i-n-type perovskite devices employing these SAMs exhibited power conversion efficiencies surpassing 21%. Notably, the best performing devices are stable under standardized maximum power point operation at 85 °C in inert atmosphere (ISOS-L-2) for more than 250 h and exhibit superior humidity resilience, maintaining ∼95% device performance even if stored in humid air in ambient conditions over months (∼3000 h, ISOS-D-1). Our work, therefore, demonstrates a strategy towards efficient and stable perovskite solar cells with easily deposited functional interlayers.
Collapse
|
11
|
Charge Transfer in c-Si(n ++)/TiO 2(ALD) at the Amorphous/Anatase Transition: A Transient Surface Photovoltage Spectroscopy Study. ACS APPLIED MATERIALS & INTERFACES 2020; 12:3140-3149. [PMID: 31829545 DOI: 10.1021/acsami.9b17592] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Electronic properties and charge transfer processes were studied in an n-Si(n++)/TiO2(ALD) system at an amorphous TiO2/anatase transition by transient surface photovoltage spectroscopy at constant photon flux. The TiO2 layers were deposited by atomic layer deposition (ALD) onto highly doped silicon (c-Si(n++)), and the phase composition of the TiO2 layers changed with increasing thickness from amorphous to the anatase polymorph as anatase crystallites started to grow at the surface. Depending on phase composition, the band gap of TiO2 correlated with the characteristic energy of exponential tails. In most cases, photogenerated electrons were separated toward the back contact. For photogeneration in c-Si(n++), electron back transfer was limited by Auger recombination with holes in the surface space charge region of c-Si(n++), and by electron transfer across the interface, either via exponentially distributed states near the conduction band edge of amorphous TiO2 or via distance-dependent recombination with holes trapped in anatase. For photogeneration in TiO2, electron back transfer was limited by trapping in TiO2. Under strong light absorption in amorphous TiO2 with anatase crystallites on top, electrons were preferentially separated toward the TiO2 surface.
Collapse
|
12
|
Quantum Chaos and Quantum Randomness-Paradigms of Entropy Production on the Smallest Scales. ENTROPY 2019; 21:e21030286. [PMID: 33267001 PMCID: PMC7514766 DOI: 10.3390/e21030286] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2018] [Revised: 02/04/2019] [Accepted: 03/10/2019] [Indexed: 11/16/2022]
Abstract
Quantum chaos is presented as a paradigm of information processing by dynamical systems at the bottom of the range of phase-space scales. Starting with a brief review of classical chaos as entropy flow from micro- to macro-scales, I argue that quantum chaos came as an indispensable rectification, removing inconsistencies related to entropy in classical chaos: bottom-up information currents require an inexhaustible entropy production and a diverging information density in phase-space, reminiscent of Gibbs' paradox in statistical mechanics. It is shown how a mere discretization of the state space of classical models already entails phenomena similar to hallmarks of quantum chaos and how the unitary time evolution in a closed system directly implies the "quantum death" of classical chaos. As complementary evidence, I discuss quantum chaos under continuous measurement. Here, the two-way exchange of information with a macroscopic apparatus opens an inexhaustible source of entropy and lifts the limitations implied by unitary quantum dynamics in closed systems. The infiltration of fresh entropy restores permanent chaotic dynamics in observed quantum systems. Could other instances of stochasticity in quantum mechanics be interpreted in a similar guise? Where observed quantum systems generate randomness, could it result from an exchange of entropy with the macroscopic meter? This possibility is explored, presenting a model for spin measurement in a unitary setting and some preliminary analytical results based on it.
Collapse
|
13
|
Characterization of BiVO4 powders and cold gas sprayed layers by surface photovoltage techniques. Catal Today 2019. [DOI: 10.1016/j.cattod.2018.02.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
14
|
Manipulation of Charge Transport by Metallic V 13 O 16 Decorated on Bismuth Vanadate Photoelectrochemical Catalyst. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1807204. [PMID: 30614577 DOI: 10.1002/adma.201807204] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2018] [Revised: 12/13/2018] [Indexed: 06/09/2023]
Abstract
Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V13 O16 , which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO4 in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V13 O16 -decorated BiVO4 hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V13 O16 . A Co-Pi coating on BiVO4 -V13 O16 further increases the photocurrent to 5.0 ± 0.5 mA cm-2 at 1.23 V versus RHE, which is among the highest reported for BiVO4 -based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge-transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co-Pi/electrolyte interface limits the charge transfer.
Collapse
|
15
|
Giant Defect-Induced Effects on Nanoscale Charge Separation in Semiconductor Photocatalysts. NANO LETTERS 2019; 19:426-432. [PMID: 30585727 DOI: 10.1021/acs.nanolett.8b04245] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
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.
Collapse
|
16
|
Imaging photogenerated charge carriers on surfaces and interfaces of photocatalysts with surface photovoltage microscopy. Chem Soc Rev 2018; 47:8238-8262. [DOI: 10.1039/c8cs00320c] [Citation(s) in RCA: 214] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Recent advances in imaging and characterizing charge separation on surfaces and interfaces of photocatalysts by surface photovoltage spectroscopy were reviewed and highlighted.
Collapse
|
17
|
Visualizing the Nano Cocatalyst Aligned Electric Fields on Single Photocatalyst Particles. NANO LETTERS 2017; 17:6735-6741. [PMID: 28967261 DOI: 10.1021/acs.nanolett.7b02799] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
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.
Collapse
|
18
|
Influence of the Grain Size on the Properties of CH 3NH 3PbI 3 Thin Films. ACS APPLIED MATERIALS & INTERFACES 2017; 9:38428-38435. [PMID: 29039197 DOI: 10.1021/acsami.7b10056] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Hybrid perovskites have already shown a huge success as an absorber in solar cells, resulting in the skyrocketing rise in the power conversion efficiency to more than η = 22%. Recently, it has been established that the crystal quality is one of the most important parameters to obtain devices with high efficiencies. However, the influence of the crystal quality on the material properties is not fully understood. Here, the influence of the morphology on electronic properties of CH3NH3PbI3 thin films is investigated. Postannealing was used to vary the average grain size continuously from ≈150 to ≈1000 nm. Secondary grain growth is thermally activated with an activation energy of Ea = 0.16 eV. The increase in the grain size leads to an enhancement of the photoluminescence, indicating an improvement in the material quality. According to surface photovoltage measurements, the charge-carrier transport length exhibits a linear increase with increasing grain size. The charge-carrier diffusion length is limited by grain boundaries. Moreover, an improved morphology leads to a drastic increase in power conversion efficiency of the devices.
Collapse
|
19
|
Update on Ignition Target Fabrication Specifications. FUSION SCIENCE AND TECHNOLOGY 2017. [DOI: 10.13182/fst41-164] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
20
|
Electrochemical generation of a molecular heterojunction. A new Zn-Porphyrin-Fullerene C 60 Polymeric Film. Electrochim Acta 2017. [DOI: 10.1016/j.electacta.2017.04.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
|
21
|
It Takes Two to Tango-Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis. ACS APPLIED MATERIALS & INTERFACES 2017; 9:17245-17255. [PMID: 28436227 DOI: 10.1021/acsami.7b00900] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Solar cells made from inorganic-organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 °C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current-voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The herein demonstrated improvements of multilayer selective contacts may serve as a general design guideline for perovskite solar cells.
Collapse
|
22
|
Transient surface photovoltage measurement over 12 orders of magnitude in time. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:053904. [PMID: 28571417 DOI: 10.1063/1.4983079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The measurement of transient surface photovoltage (SPV) signals in a fixed capacitor arrangement over 12 orders of magnitude in time has been demonstrated for a SnO2:F/TiO2/In2S3 layer system under high vacuum. For this purpose, a high impedance buffer with a bandwidth above 200 MHz and an effective input resistance of 200-700 TΩ has been developed. Fast separation of photo generated charge carriers within ns and very slow relaxation of SPV signals excited with short laser pulses and the measurement of SPV spectra under continuous illumination with a halogen lamp were demonstrated.
Collapse
|
23
|
Enhancement of photocurrent in an ultra-thin perovskite solar cell by Ag nanoparticles deposited at low temperature. RSC Adv 2017. [DOI: 10.1039/c6ra25149h] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
22.2% relative enhancement of photocurrent in ultra-thin perovskite solar cells by one step incorporation of plasmonic silver nanoparticles.
Collapse
|
24
|
Minimal renal toxicity after Rituximab DHAP with a modified cisplatin application scheme in patients with relapsed or refractory diffuse large B-cell lymphoma. BMC Cancer 2016; 16:267. [PMID: 27067641 PMCID: PMC4828891 DOI: 10.1186/s12885-016-2289-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 03/22/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Rituximab (R) in combination with DHAP is a widely accepted salvage regimen for patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL). A common adverse effect of this protocol is renal toxicity which may result in treatment discontinuation. Assuming that a lower single dose of cisplatin over several days would reduce renal toxicity, our institution has chosen to administer cisplatin in a dosage of 25 mg/m(2) per day as a 3-h infusion over 4 consecutive days. METHODS In this study, we analyzed the renal function of 122 patients with relapsed or refractory DLBCL treated with R-DHAP at our institution. Overall, 256 R-DHAP cycles were administered. 31 (25%), 61 (50%), 14 (12%) and 16 (13%) patients received one, two, three or four R-DHAP courses, respectively. RESULTS A glomerular filtration rate (GFR) decrease was observed after each R-DHAP cycle. However, in none of the subgroups the median GFR was lower than 60 ml/min/1.73 m(2). In most patients, only renal impairment stage I and II was observed. Renal impairment stage III was seen in 10% and stage IV only in 1% of patients. CONCLUSION We conclude that a modified R-DHAP regimen with administration of cisplatin 25 mg/m(2) over 4 consecutive cycles leads only to minimal renal toxicity.
Collapse
|
25
|
Photoinduced charge separation in organic-inorganic hybrid system: C 60 -containing electropolymer / CdSe-quantum dots. Electrochim Acta 2015. [DOI: 10.1016/j.electacta.2015.05.029] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
26
|
|
27
|
Classical and quantum chaotic angular-momentum pumps. PHYSICAL REVIEW LETTERS 2015; 114:094101. [PMID: 25793818 DOI: 10.1103/physrevlett.114.094101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Indexed: 06/04/2023]
Abstract
We study directed transport of charge and intrinsic angular momentum by periodically driven scattering in the regime of fast and strong driving. A spin-orbit coupling through a kicked magnetic field confined to a compact region in space leads to irregular scattering and triggers spin flips in a spatially asymmetric manner which allows us to generate polarized currents. The dynamical mechanisms responsible for the spin separation carry over to the quantum level and give rise to spin pumping. Our theory based on the Floquet formalism is confirmed by numerical solutions of the time-dependent inhomogeneous Schrödinger equation with a continuous source term.
Collapse
|
28
|
Electrochemical Generation of Porphyrin-Porphyrin and Porphyrin-C60 Polymeric Photoactive Organic Heterojunctions. Electrochim Acta 2014. [DOI: 10.1016/j.electacta.2014.04.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
29
|
Optical and electronic properties of pyrite nanocrystal thin films: the role of ligands. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2014; 10:1194-1201. [PMID: 24395590 DOI: 10.1002/smll.201302333] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 11/24/2013] [Indexed: 06/03/2023]
Abstract
Pyrite nanocrystals are currently considered as a promising material for large scale photovoltaic applications due to their non-toxicity and large abundance. While scalable synthetic routes for phase-pure and shape controlled colloidal pyrite nanocrystals have been reported, their use in solar cells has been hampered by the detrimental effects of their surface defects. Here, we report a systematic study of optical and electronic properties of pyrite nanocrystal thin films employing a series of different ligands varying both the anchor and bridging group. The effect of the ligands on the optical and electronic properties is investigated by UV-vis/NIR absorption spectroscopy, current voltage characteristic measurements and surface photovoltage spectroscopy. We find that the optical absorption is mainly determined by the anchor group. The absorption onset in the thin films shifts up to ∼100 meV to the red. This is attributed to changes in the dielectric environment induced by different anchors. The conductivity and photoconductivity, on the other hand, are determined by combined effects of anchor and bridging group, which modify the effective hopping barrier. Employing different ligands, the differential conductance varies over four orders of magnitude. The largest redshift and differential conductance are observed for ammonium sulfides and thiolated aromatic linkers. Pyridine and long chain amines, on the other hand, lead to smaller modifications. Our findings highlight the importance of surface functionalization and interparticle electronic coupling in the use of pyrite nanocrystals for photovoltaic devices.
Collapse
|
30
|
Charge separation at disordered semiconductor heterojunctions from random walk numerical simulations. Phys Chem Chem Phys 2014; 16:4082-91. [DOI: 10.1039/c3cp54237h] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
31
|
High performance PbS Quantum Dot Sensitized Solar Cells exceeding 4% efficiency: the role of metal precursors in the electron injection and charge separation. Phys Chem Chem Phys 2013; 15:13835-43. [PMID: 23677043 DOI: 10.1039/c3cp51651b] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Here we report the preparation of high performance Quantum Dot Sensitized Solar Cells (QDSCs) based on PbS-CdS co-sensitized nanoporous TiO2 electrodes. QDs were directly grown on the TiO2 mesostructure by the Successive Ionic Layer Absorption and Reaction (SILAR) technique. This method is characterized by a fast deposition rate which involves random crystal growth and poor control of the defect states and lattice mismatch in the QDs limiting the quality of the electrodes for photovoltaic applications. In this work we demonstrate that the nature of the metallic precursor selected for SILAR has an active role in both the QD's deposition rate and the defect's distribution in the material, with important consequences for the final photovoltaic performance of the device. For this purpose, acetate and nitrate salts were selected as metallic precursors for the SILAR deposition and films with similar absorption properties and consequently with similar density of photogenerated carriers were studied. Under these conditions, ultrafast carrier dynamics and surface photovoltage spectroscopy reveal that the use of acetate precursors leads to higher injection efficiency and lower internal recombination due to contribution from defect states. This was corroborated in a complete cell configuration with films sensitized with acetate precursors, achieving unprecedented photocurrents of ~22 mA cm(-2) and high power conversion efficiency exceeding 4%, under full 1 sun illumination.
Collapse
|
32
|
Abstract
Disorder in conjugated polymers is a general drawback that limits their use in organic electronics. We show that an archetypical conjugated polymer, MEH-PPV, enhances its local structural and electronic order upon addition of an electronic acceptor, trinitrofluorenone (TNF). First, acceptor addition in MEH-PPV results in a highly structured XRD pattern characteristic for semicrystalline conjugated polymers. Second, the surface roughness of the MEH-PPV films increases upon small acceptor addition, implying formation of crystalline nanodomains. Third, the low-frequency Raman features of the polymer are narrowed upon TNF addition and indicate decreased inhomogeneous broadening. Finally, the photoinduced absorption and surface photovoltage spectroscopy data show that photoexcited and dark polymer intragap electronic states assigned to deep defects disappear in the blend. We relate the enhanced order to formation of a charge-transfer complex between MEH-PPV and TNF in the electronic ground state. These findings may be of high importance to control structural properties as they demonstrate an approach to increasing the order of a conjugated polymer by using an acceptor additive.
Collapse
|
33
|
Surface aspects of sol–gel derived hematite films for the photoelectrochemical oxidation of water. Phys Chem Chem Phys 2013; 15:1389-98. [DOI: 10.1039/c2cp42651j] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
34
|
Junction formation of Cu(3)BiS(3) investigated by Kelvin probe force microscopy and surface photovoltage measurements. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2012; 3:277-284. [PMID: 22497001 PMCID: PMC3323917 DOI: 10.3762/bjnano.3.31] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 02/21/2012] [Indexed: 05/31/2023]
Abstract
Recently, the compound semiconductor Cu(3)BiS(3) has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu(3)BiS(3) absorber layer and the junction formation with CdS, ZnS and In(2)S(3) buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20-100 nm, and a considerably smaller work-function distribution for In(2)S(3) compared to that of CdS and ZnS. For In(2)S(3) and CdS buffer layers the KPFM experiments indicate negatively charged Cu(3)BiS(3) grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In(2)S(3) buffer layer. Our findings indicate that Cu(3)BiS(3) may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased.
Collapse
|
35
|
Photoinduced charge separation in donor–acceptor spiro compounds at metal and metal oxide surfaces: application in dye-sensitized solar cell. RSC Adv 2012. [DOI: 10.1039/c2ra00995a] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
|
36
|
Acetylation of p53 is involved in VPA induced death of AML cells. KLINISCHE PADIATRIE 2011. [DOI: 10.1055/s-0031-1277066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
37
|
Abstract
AbstractIn previous work we reported on the observation of continuously tunable photoluminescence in Si+-implanted SiO2-films with moderate intensities. In this paper we demonstrate improved performance of such samples. The photoluminescence intensity increases abruptly up to two orders of magnitude when the anneal temperature is elevated to values higher than 1000…1100°C. This strong photoluminescence degrades less than that of porous silicon. Very fine tunability in the spectral range from 2.1 eV to 1.3 eV is achieved in samples implanted with a graded dose. In the analysis of the results we try to distinguish between the contributions of the Si-nanocrystals and of the oxide related defects.
Collapse
|
38
|
|
39
|
|
40
|
Abstract
We present a comprehensive study of semiclassical phase-space propagation in the Wigner representation, emphasizing numerical applications, in particular as an initial-value representation. Two semiclassical approximation schemes are discussed. The propagator of the Wigner function based on van Vleck's approximation replaces the Liouville propagator by a quantum spot with an oscillatory pattern reflecting the interference between pairs of classical trajectories. Employing phase-space path integration instead, caustics in the quantum spot are resolved in terms of Airy functions. We apply both to two benchmark models of nonlinear molecular potentials, the Morse oscillator and the quartic double well, to test them in standard tasks such as computing autocorrelation functions and propagating coherent states. The performance of semiclassical Wigner propagation is very good even in the presence of marked quantum effects, e.g., in coherent tunneling and in propagating Schrodinger cat states, and of classical chaos in four-dimensional phase space. We suggest options for an effective numerical implementation of our method and for integrating it in Monte-Carlo-Metropolis algorithms suitable for high-dimensional systems.
Collapse
|
41
|
Charge Separation in Type II Tunneling Multilayered Structures of CdTe and CdSe Nanocrystals Directly Proven by Surface Photovoltage Spectroscopy. J Am Chem Soc 2010; 132:5981-3. [DOI: 10.1021/ja101629c] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
42
|
Nanoscale interaction between CdSe or CdTe nanocrystals and molecular dyes fostering or hindering directional charge separation. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2010; 6:221-225. [PMID: 19957285 DOI: 10.1002/smll.200901494] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
|
43
|
Time-domain scars: resolving the spectral form factor in phase space. PHYSICAL REVIEW LETTERS 2009; 102:150401. [PMID: 19518605 DOI: 10.1103/physrevlett.102.150401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Indexed: 05/27/2023]
Abstract
We study the relationship of the spectral form factor with quantum as well as classical probabilities to return. Defining a quantum return probability in phase space as a trace over the propagator of the Wigner function allows us to identify and resolve manifolds in phase space that contribute to the form factor. They can be associated with classical invariant manifolds such as periodic orbits, but also to nonclassical structures such as sets of midpoints between periodic points. In contrast to scars in wave functions, these features are not subject to the uncertainty relation and therefore need not show any smearing. They constitute important exceptions from a continuous convergence in the classical limit of the Wigner towards the Liouville propagator. We support our theory with numerical results for the quantum cat map and the harmonically driven quartic oscillator.
Collapse
|
44
|
Long duration backlighter experiments at Omega. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2008; 79:10E915. [PMID: 19044570 DOI: 10.1063/1.2981173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We have successfully demonstrated a 7.5 ns duration pinhole-apertured backlighter at the Omega laser facility. Pinhole-apertured point-projection backlighting for 8 ns will be useful for imaging evolving features in experiments at the National Ignition Facility. The backlighter consisted of a 20 microm diameter pinhole in a 75 microm thick Ta substrate separated from a Zn emitter (9 keV) by a 400 microm thick high-density carbon piece. The carbon prevented the shock from the laser-driven surface from reaching the substrate before 8 ns and helped minimize x-ray ablation of the pinhole substrate. Grid wires in x-ray framing camera images of a gold grid have a source-limited resolution significantly smaller than the pinhole diameter due to the high aspect ratio of the pinhole, but do not become much smaller at late times.
Collapse
|
45
|
Porosity dependence of electron percolation in nanoporous TiO2 layers. J Chem Phys 2008; 128:064703. [DOI: 10.1063/1.2837807] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
46
|
Interpretation of diffusion coefficients in nanostructured materials from random walk numerical simulation. Phys Chem Chem Phys 2008; 10:4478-85. [DOI: 10.1039/b719821c] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
47
|
Exploring the electronic structure of nitrogen-modified TiO2 photocatalysts through photocurrent and surface photovoltage studies. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.05.022] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
48
|
Optically induced switch of the surface work function in TiO2/porphyrin–C60dyad system. ACTA ACUST UNITED AC 2007. [DOI: 10.1039/b617944d] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
49
|
Continuous time random walk simulation of short-range electron transport in TiO2 layers compared with transient surface photovoltage measurements. J Photochem Photobiol A Chem 2006. [DOI: 10.1016/j.jphotochem.2006.04.029] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
50
|
Abstract
Layers of porous TiO(2) fabricated by electrophoretic deposition at different temperatures with subsequent sintering in air were investigated by transient photocurrent measurements in aqueous electrolyte. The effective diffusion coefficient of excess electrons changed between 1.6 x 10(-5) and 1.4 x 10(-4) cm(2)/s depending strongly on the solution temperature during the TiO(2) layer deposition. Characterization, in terms of average degree of preferred orientation, shows that low deposition temperature results in orientation of the nanocrystals forming the porous film. Consequently, the increase of effective diffusion coefficient is attributed to a higher degree of ordering in the nanoporous TiO(2) layer.
Collapse
|