Excitonic Processes in Organic Semiconductors and Their Applications in Organic Photovoltaic and Light Emitting Devices

Narayan, Monishka Rita; Singh, Jai

doi:10.1007/978-981-287-131-2_8

Cited by 7 publications

(2 citation statements)

References 60 publications

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“…Energy transfer in organic compounds usually occurs by either a Förster or a Dexter mechanism, while the former process mostly occurs in the case of singlet and the latter in the case of triplet excitations. The Förster transfer, which occurs via dipole-dipole interaction, shows a rate constant 19 k…”

Section: Introductionmentioning

confidence: 99%

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Photoexcited organic molecules $en~route$ to highly efficient autoionization

Vempati,

Bogner,

Richter

et al. 2019

Preprint

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The conversion of optical and electrical energy in novel materials is key to modern optoelectronic and light-harvesting applications. Here, we investigate the equilibration dynamics of photoexcited 2,7-bis(biphenyl-4-yl)-2',7'-ditertbutyl-9,9'-spirobifluorene (SP6) molecules adsorbed on ZnO(10-10) using femtosecond time-resolved two-photon photoelectron (2PPE) and optical spectroscopy. We find that, after initial ultrafast relaxation on fs and ps timescales, an optically dark state is populated, likely the SP6 triplet (T) state, that undergoes Dexter-type energy transfer (r Dex = 1.3 nm) and exhibits a long decay time of 0.1 s. Because of this long lifetime a photostationary state with average T-T distances below 2 nm is established at excitation densities in the 10 20 cm −2 s −1 range. This large density enables decay by T-T annihilation (TTA) mediating autoionization despite an extremely low TTA rate of k TTA = 4.5 • 10 −26 m 3 s −1 . The large external quantum efficiency of the autoionization process (up to 15 %) and photocurrent densities in the mA cm −2 range offer great potential for light-harvesting applications.

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Section: Introductionmentioning

confidence: 99%

“…These require wave function overlap, which is why Dexter transfer is a short-range process, usually occuring across few nanometer distances. The rate constant can be written as 19 k Dex…”

Section: Introductionmentioning

confidence: 99%

Photoexcited organic molecules $en~route$ to highly efficient autoionization

Vempati,

Bogner,

Richter

et al. 2019

Preprint

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Organic Semiconductors at the University of Washington: Advancements in Materials Design and Synthesis and toward Industrial Scale Production

et al. 2019

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Second-order NLO effects can be separated into two broad categories. The first category involves how light waves interact with an NLO medium, and it includes second-harmonic generation, sum-frequency generation, difference-frequency generation, and optical rectification. In the second category, called the electro-optic effect, an applied external electric field induces a linear change in refractive index of the NLO material. [10] Applications of the EO effect include phase modulators, Mach-Zehnder interferometers (Figure 1), in-phase-quadrature modulators, resonant antennae modulators, and ring resonators (wavelength division multiplexers), which are incredibly important commercially for transducing electrical to optical signals at high frequencies (GHz) for telecommunications over photonics fiber/wireless networks. The dominant EO material used commercially is lithium niobate, which is an inorganic crystal; however, organic materials have an inherent advantage for high-frequency applications as the polarization response in an organic molecule is dependent on the motions of electrons, which yield response times much faster (10 −14 s) than the polarization response times of inorganic EO materials (10 −10 s) which depend on the motions of ions. [10] Over the past ≈20 years, UW researchers (in the groups of Profs.

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An Alternative Approach to Simulate the Power Conversion Efficiency of Bulk Heterojunction Organic Solar Cells

Ram

Ompong

Rad

et al. 2020

Physica Status Solidi (a)

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An alternative approach to simulate the power conversion efficiency (η PCE) of bulk heterojunction organic solar cells (BHJ OSCs), as a product of efficiencies of absorption (η abs), dissociation (η dis), and extraction (η ext), is presented. Although η abs and η dis do not directly contribute to the simulation of η PCE , the approach enables us in understanding their roles in optimizing the power conversion efficiency of BHJ OSCs. This method is applied to simulate η PCE as a function of the thickness of active layer for three different BHJ OSC structures, one with a fullerene acceptor and two with two different nonfullerene acceptors. The results are found to be in good agreement with those from the previous simulation and experimental works and are expected to be useful in optimizing the thickness of the active layer.

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Excitonic Processes in Organic Semiconductors and Their Applications in Organic Photovoltaic and Light Emitting Devices

Cited by 7 publications

References 60 publications

Photoexcited organic molecules $en~route$ to highly efficient autoionization

Photoexcited organic molecules $en~route$ to highly efficient autoionization

Organic Semiconductors at the University of Washington: Advancements in Materials Design and Synthesis and toward Industrial Scale Production

An Alternative Approach to Simulate the Power Conversion Efficiency of Bulk Heterojunction Organic Solar Cells

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