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Xu Z, Hou B, Zhao F, Suo S, Liu Y, Shi H, Cai Z, Hill CL, Musaev DG, Mecklenburg M, Cronin SB, Lian T. Direct In Situ Measurement of Quantum Efficiencies of Charge Separation and Proton Reduction at TiO 2-Protected GaP Photocathodes. J Am Chem Soc 2023; 145:2860-2869. [PMID: 36715560 PMCID: PMC9912250 DOI: 10.1021/jacs.2c10578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Photoelectrochemical solar fuel generation at the semiconductor/liquid interface consists of multiple elementary steps, including charge separation, recombination, and catalytic reactions. While the overall incident light-to-current conversion efficiency (IPCE) can be readily measured, identifying the microscopic efficiency loss processes remains difficult. Here, we report simultaneous in situ transient photocurrent and transient reflectance spectroscopy (TRS) measurements of titanium dioxide-protected gallium phosphide photocathodes for water reduction in photoelectrochemical cells. Transient reflectance spectroscopy enables the direct probe of the separated charge carriers responsible for water reduction to follow their kinetics. Comparison with transient photocurrent measurement allows the direct probe of the initial charge separation quantum efficiency (ϕCS) and provides support for a transient photocurrent model that divides IPCE into the product of quantum efficiencies of light absorption (ϕabs), charge separation (ϕCS), and photoreduction (ϕred), i.e., IPCE = ϕabsϕCSϕred. Our study shows that there are two general key loss pathways: recombination within the bulk GaP that reduces ϕCS and interfacial recombination at the junction that decreases ϕred. Although both loss pathways can be reduced at a more negative applied bias, for GaP/TiO2, the initial charge separation loss is the key efficiency limiting factor. Our combined transient reflectance and photocurrent study provides a time-resolved view of microscopic steps involved in the overall light-to-current conversion process and provides detailed insights into the main loss pathways of the photoelectrochemical system.
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Affiliation(s)
- Zihao Xu
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States,ZJU-Hangzhou
Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, Zhejiang310014, China
| | - Bingya Hou
- Department
of Electrical Engineering, University of
South California, 3710 McClintock Ave, Los Angeles, California90089, United States
| | - Fengyi Zhao
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Sa Suo
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Yawei Liu
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Haotian Shi
- Department
of Chemistry, University of South California, 3710 McClintock Ave, Los Angeles, California90089, United States
| | - Zhi Cai
- Department
of Electrical Engineering, University of
South California, 3710 McClintock Ave, Los Angeles, California90089, United States
| | - Craig L. Hill
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Djamaladdin G. Musaev
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States,Cherry
L. Emerson Centre for Scientific Computation, Emory University, 1515 Dickey Drive, Atlanta, Georgia30322, United
States
| | - Matthew Mecklenburg
- Core Center
of Excellence in Nano Imaging (CNI), University
of South California, 814 Bloom Walk, Los Angeles, California90089, United States
| | - Stephen B. Cronin
- Department
of Electrical Engineering, University of
South California, 3710 McClintock Ave, Los Angeles, California90089, United States,Department
of Chemistry, University of South California, 3710 McClintock Ave, Los Angeles, California90089, United States,
| | - Tianquan Lian
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States,
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Deng GH, Wei Q, Qian Y, Zhang T, Leng X, Rao Y. Development of interface-/surface-specific two-dimensional electronic spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:023104. [PMID: 33648131 DOI: 10.1063/5.0019564] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 01/26/2021] [Indexed: 06/12/2023]
Abstract
Structures, kinetics, and chemical reactivities at interfaces and surfaces are key to understanding many of the fundamental scientific problems related to chemical, material, biological, and physical systems. These steady-state and dynamical properties at interfaces and surfaces require even-order techniques with time-resolution and spectral-resolution. Here, we develop fourth-order interface-/surface-specific two-dimensional electronic spectroscopy, including both two-dimensional electronic sum frequency generation (2D-ESFG) spectroscopy and two-dimensional electronic second harmonic generation (2D-ESHG) spectroscopy, for structural and dynamics studies of interfaces and surfaces. The 2D-ESFG and 2D-ESHG techniques were based on a unique laser source of broadband short-wave IR from 1200 nm to 2200 nm from a home-built optical parametric amplifier. With the broadband short-wave IR source, surface spectra cover most of the visible light region from 480 nm to 760 nm. A translating wedge-based identical pulses encoding system (TWINs) was introduced to generate a phase-locked pulse pair for coherent excitation in the 2D-ESFG and 2D-ESHG. As an example, we demonstrated surface dark states and their interactions of the surface states at p-type GaAs (001) surfaces with the 2D-ESFG and 2D-ESHG techniques. These newly developed time-resolved and interface-/surface-specific 2D spectroscopies would bring new information for structure and dynamics at interfaces and surfaces in the fields of the environment, materials, catalysis, and biology.
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Affiliation(s)
- Gang-Hua Deng
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Qianshun Wei
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Yuqin Qian
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Tong Zhang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Xuan Leng
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Yi Rao
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
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Mannebach EM, Duerloo KAN, Pellouchoud LA, Sher MJ, Nah S, Kuo YH, Yu Y, Marshall AF, Cao L, Reed EJ, Lindenberg AM. Ultrafast electronic and structural response of monolayer MoS2 under intense photoexcitation conditions. ACS NANO 2014; 8:10734-42. [PMID: 25244589 DOI: 10.1021/nn5044542] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
We report on the dynamical response of single layer transition metal dichalcogenide MoS2 to intense above-bandgap photoexcitation using the nonlinear-optical second order susceptibility as a direct probe of the electronic and structural dynamics. Excitation conditions corresponding to the order of one electron-hole pair per unit cell generate unexpected increases in the second harmonic from monolayer films, occurring on few picosecond time-scales. These large amplitude changes recover on tens of picosecond time-scales and are reversible at megahertz repetition rates with no photoinduced change in lattice symmetry observed despite the extreme excitation conditions.
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Affiliation(s)
- Ehren M Mannebach
- Department of Materials Science and Engineering, Stanford University , Stanford, California 94305, United States
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Son DH, Wittenberg JS, Banin U, Alivisatos AP. Second harmonic generation and confined acoustic phonons in highly excited semiconductor nanocrystals. J Phys Chem B 2007; 110:19884-90. [PMID: 17020374 DOI: 10.1021/jp062028o] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The photo-induced enhancement of second harmonic generation and the effect of nanocrystal shape and pump intensity on confined acoustic phonons in semiconductor nanocrystals have been investigated with time-resolved scattering and absorption measurements. The second harmonic signal showed a sublinear increase of the second-order susceptibility with respect to the pump pulse energy, indicating a reduction of the effective one-electron second-order nonlinearity with increasing electron-hole density in the nanocrystals. The coherent acoustic phonons in spherical and rod-shaped semiconductor nanocrystals were detected in a time-resolved absorption measurement. Both nanocrystal morphologies exhibited oscillatory modulation of the absorption cross section, the frequency of which corresponded to their coherent radial breathing modes. The amplitude of the oscillation also increased with the level of photoexcitation, suggesting an increase in the amplitude of the lattice displacement as well.
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Affiliation(s)
- Dong Hee Son
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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McClelland A, Fomenko V, Borguet E. Ultrafast Hot-Carrier Dynamics at Chemically Modified Ge Interfaces Probed by SHG. J Phys Chem B 2006; 110:19784-7. [PMID: 17020361 DOI: 10.1021/jp0460700] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Time-resolved second-harmonic generation (SHG) was used to study the hot-carrier dynamics and nonlinear optical properties of S-terminated and Cl-terminated Ge(111) interfaces on the femtosecond time scale. The hot-carrier second-order nonlinear optical susceptibilities were determined to be 720 +/- 50 times greater than the valence-band second-order nonlinear optical susceptibilities for the Ge(111)-S system and 880 +/- 100 times greater in the Ge(111)-Cl system. Furthermore, the ground- and excited-state second-order nonlinear optical susceptibilities are suggested to be out of phase for Ge(111)-S and Ge(111)-Cl systems, leading to a pump-induced decrease in the SHG signal as opposed to the increase in the SHG signal observed in the Ge(111)-GeO2 system. Although the SHG response reaches a steady state in 415 +/- 90 fs in the Ge(111)-GeO2 system, a faster response is observed in the Ge(111)-S system, 220 +/- 85 fs, and in the Ge(111)-Cl system, 172 +/- 50 fs. This suggests significantly faster carrier cooling at the Ge(111)-Cl and Ge(111)-S interfaces, with significant implications for hot-carrier mediated device degradation, and migration to high-K dielectrics.
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Affiliation(s)
- Arthur McClelland
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA
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Beyer O, Maxein D, Buse K, Sturman B, Hsieh HT, Psaltis D. Investigation of nonlinear absorption processes with femtosecond light pulses in lithium niobate crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:056603. [PMID: 16089664 DOI: 10.1103/physreve.71.056603] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Indexed: 05/03/2023]
Abstract
The propagation of high-power femtosecond light pulses in lithium niobate crystals (LiNb O3 ) is investigated experimentally and theoretically in collinear pump-probe transmission experiments. It is found within a wide intensity range that a strong decrease of the pump transmission coefficient at wavelength 388 nm fully complies with the model of two-photon absorption; the corresponding nonlinear absorption coefficient is beta(p) approximately = 3.5 cm/GW. Furthermore, strong pump pulses induce a considerable absorption for the probe at 776 nm. The dependence of the probe transmission coefficient on the time delay Delta t between probe and pump pulses is characterized by a narrow dip (at Delta t approximately = 0) and a long (on the picosecond time scale) lasting plateau. The dip is due to direct two-photon transitions involving pump and probe photons; the corresponding nonlinear absorption coefficient is beta(r) approximately = 0.9 cm/GW. The plateau absorption is caused by the presence of pump-excited charge carriers; the effective absorption cross section at 776 nm is sigma(r) approximately = 8 x 10(-18) cm(2). The above nonlinear absorption parameters are not strongly polarization sensitive. No specific manifestations of the relaxation of hot carriers are found for a pulse duration of approximately = 0.24 ps.
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Affiliation(s)
- O Beyer
- Institute of Physics, University of Bonn, Wegelerstr. 8, D-53115 Bonn, Germany.
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