Optical Probe of Charge Separation at Organic/Inorganic Semiconductor Interfaces

Park, H.; Gutierrez, Marlene; Wu, Xiaoxi; Kim, W.; Zhu, Xiaoyang

doi:10.1021/jp4029408

Cited by 26 publications

(36 citation statements)

References 37 publications

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“…EFISH 22,23 is a fourwave mixing process: two optical fields at frequency o mix with a direct current field to give signal at frequency 2o. We have successfully implemented this in the time-resolved mode to detect transient electric fields resulting from charge separation at donor/ acceptor interfaces 21,[24][25][26][27] . The open circles in Fig.…”

Section: Resultsmentioning

confidence: 99%

Harvesting singlet fission for solar energy conversion via triplet energy transfer

Tritsch

Chan

et al. 2013

Nat Commun

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The efficiency of a conventional solar cell may be enhanced if one incorporates a molecular material capable of singlet fission, that is, the production of two triplet excitons from the absorption of a single photon. To implement this, we need to successfully harvest the two triplets from the singlet fission material. Here we show in the tetracene (Tc)/copper phthalocyanine (CuPc) model system that triplets produced from singlet fission in the former can transfer to the later on the timescale of 45±5 ps. However, the efficiency of triplet energy transfer is limited by a loss channel due to faster formation (400±100 fs) and recombination (2.6±0.5 ps) of charge transfer excitons at the interface. These findings suggest a design principle for efficient energy harvesting from singlet fission: one must reduce interfacial area between the two organic chromophores to minimize charge transfer/recombination while optimizing light absorption, singlet fission and triplet rather than singlet transfer.

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Section: Resultsmentioning

confidence: 99%

Harvesting singlet fission for solar energy conversion via triplet energy transfer

Tritsch

Chan

et al. 2013

Nat Commun

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“…This process is also called electric-field induced SHG (EFISH) process. 13,15,48,[91][92][93][94][95][96][97][98][99][100][101] The former was excluded since the two surface states exhibit almost the same population rate in the early time upon the photoexcitation, as displayed in Fig. 5(c).…”

Section: Fig 4 Comparison Of Kinetic Profiles Of the Surface And Bumentioning

confidence: 99%

“…Recent studies showed that charge transfer occurs at semiconductor/organic thin film interfaces with timeresolved electric-field induced second harmonic generation (SHG), with the loss of spectral information. [13][14][15][16] Early efforts have also demonstrated the ultrafast relaxation of the surface photo-voltage (SPV) effect on semiconductors by timeresolved photoemission spectroscopy. [17][18][19] The time evolution of the electric field was demonstrated in the surface layer of semiconductors by measuring the kinetic-energy shifts of photoelectrons.…”

Section: Introductionmentioning

confidence: 99%

Development of ultrafast broadband electronic sum frequency generation for charge dynamics at surfaces and interfaces

Deng

Qian

Rao

2019

The Journal of Chemical Physics

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Understandings of population and relaxation of charges at surfaces and interfaces are essential to improve charge collection efficiency for energy conversion, catalysis, and photosynthesis. Existing time-resolved surface and interface tools are limited to either under ultrahigh vacuum or in a narrow wavelength region with the loss of spectral information. There lacks an efficient time-resolved surface/interface-specific electronic spectroscopy under ambient conditions for the ultrafast surface/interface dynamics. Here we developed a novel technique for surface/interface-specific broadband electronic sum frequency generation (ESFG). The broadband ESFG was based on a stable two-stage BiB 3 O 6 crystal-based optical parametric amplifier, which generates a strong broadband shortwave infrared (SWIR) from 1200 nm to 2400 nm. A resultant surface spectrum covers almost all visible light from 480 nm to 760 nm, combined a broadband electronic second harmonic generation (ESHG) with the ESFG from the SWIR laser source. We further developed the steady-state and transient broadband ESFG and ESHG techniques to investigate the structure and dynamics of charges at oxidized p-type GaAs (100) semiconductor surfaces, as an example. Both the steady-state and transient experiments have shown that two surface states exist inside the bandgap of the GaAs. The kinetic processes at the GaAs surface include both the population and recombination of the surface states after photoexcitation, in addition to the build-up of the space photo-voltage (SPV). The build-up SPV occurs with a rate of 0.56 ± 0.07 ps −1 , while the population rate of the surface states exhibits a two-body behavior with a rate constant of (0.012 ± 0.002) × 10 12 s −1 cm 2. The photo-generated electron-hole pairs near the surface recombine with a rate of 0.002 ± 0.0002 ps −1 for the oxidized p-type GaAs (100). All the methodologies developed here are readily applied to any optically accessible interfaces and surfaces, in particular buried interfaces under ambient conditions.

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“…Besides, the difference transmission signal (Δ T / T ) is heavily suppressed by the absorption of surface excited carriers to cause the difficulties for the analyses. Comparing with the transmission configuration for the practical applications, the measurements of Δ R(ω )/ R(ω ) in the reflection configuration are more widely applied to various types of materials, including opaque materials, transparent materials9, bulk610, thin films11, and hetero-structures1213. Moreover, the ultra-broadband and 70-fs time-resolved spectra developed in this study are wide enough to provide more reliable fitting results and able to fully reveal the evolution of most of the features in spectra.…”

mentioning

confidence: 99%

Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy

Yeh

Shirai

et al. 2017

Sci Rep

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In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200–5000 cm−1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm−1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.

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Optical Probe of Charge Separation at Organic/Inorganic Semiconductor Interfaces

Cited by 26 publications

References 37 publications

Harvesting singlet fission for solar energy conversion via triplet energy transfer

Harvesting singlet fission for solar energy conversion via triplet energy transfer

Development of ultrafast broadband electronic sum frequency generation for charge dynamics at surfaces and interfaces

Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy

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