Diffusion and relaxation of energy in disordered organic and inorganic materials

Movaghar, B.; Grünewald, Marcus; Ries, B.; Bäßler, H.; Würtz, D.

doi:10.1103/physrevb.33.5545

Cited by 272 publications

(188 citation statements)

References 27 publications

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“…A stretched exponential decay is expected for films that possess an ensemble of ordered and disordered regions and a correspondingly broad distribution of decay times. 70, 71 As we are particularly interested in the initial signal changes, we treat the ultrafast component separately by fitting the GSB and the singlet exciton absorption according to the function…”

Section: Temporal Evolution Of the Charge Generation Processmentioning

confidence: 99%

“…Therefore, the use of a stretched exponential fit for the decay kinetics is justified. 71 The fit curves obtained are indicated as solid colored curves in Figure 6a. The fit parameters A 1 , A SE , τ 1 , τ SE are listed in Table 2 for the ΔOD signals at 660 nm (polaron), 1000 nm (exciton), and 550 nm (GSB).…”

Section: Temporal Evolution Of the Charge Generation Processmentioning

confidence: 99%

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Role of Structural Order and Excess Energy on Ultrafast Free Charge Generation in Hybrid Polythiophene/Si Photovoltaics Probed in Real Time by Near-Infrared Broadband Transient Absorption

et al. 2011

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Despite the central role of light absorption and the subsequent generation of free charge carriers in organic and hybrid organicÀinorganic photovoltaics, the precise process of this initial photoconversion is still debated. We employ a novel broadband (UVÀVisÀNIR) transient absorption spectroscopy setup to probe charge generation and recombination in the thin films of the recently suggested hybrid material combination poly(3-hexylthiophene)/silicon (P3HT/Si) with 40 fs time resolution. Our approach allows for monitoring the time evolution of the relevant transient species under various excitation intensities and excitation wavelengths. Both in regioregular (RR) and regiorandom (RRa) P3HT, we observe an instant (<40 fs) creation of singlet excitons, which subsequently dissociate to form polarons in 140 fs. The quantum yield of polaron formation through dissociation of delocalized excitons is significantly enhanced by adding Si as an electron acceptor, revealing ultrafast electron transfer from P3HT to Si. P3HT/Si films with aggregated RR-P3HT are found to provide free charge carriers in planar as well as in bulk heterojunctions, and losses are due to nongeminate recombination. In contrast for RRa-P3HT/Si, geminate recombination of bound carriers is observed as the dominant loss mechanism. Site-selective excitation by variation of pump wavelength uncovers an energy transfer from P3HT coils to aggregates with a 1/e transfer time of 3 ps and reveals a factor of 2 more efficient polaron formation using aggregated RR-P3HT compared to disordered RRa-P3HT. Therefore, we find that polymer structural order rather than excess energy is the key criterion for free charge generation in hybrid P3HT/Si solar cells.

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Section: Temporal Evolution Of the Charge Generation Processmentioning

confidence: 99%

Section: Temporal Evolution Of the Charge Generation Processmentioning

confidence: 99%

Role of Structural Order and Excess Energy on Ultrafast Free Charge Generation in Hybrid Polythiophene/Si Photovoltaics Probed in Real Time by Near-Infrared Broadband Transient Absorption

et al. 2011

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“…In this case, phonon-assisted tunneling between energetically disordered sites described by Miller-Abrahams transfer theory is more appropriate [14,19]. Moreover, dispersive triplet diffusion is prevalent at low temperatures [11,20,21]. Following excitation, triplets relax towards the low-energy tail of the DOS, resulting in a hopping towards acceptor sites at lower energy [11,13].…”

Section: Temperatures Below the Transition (Ie T < T Trans ) Multimentioning

confidence: 99%

Temperature dependence of the exciton dynamics inDCM2:Alq3

2014

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We study the temperature dependence of the triplet and singlet exciton dynamics in the archetype small molecule fluorescent guest-host system, tris(8-hydroxyquinolinato) aluminum (Alq 3 ) doped with 4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran (DCM2). We develop a comprehensive model of the exciton dynamics, and use it to fit the transient photoluminescence under different pulsed optical pumping in the temperature range of 80 K< T< 295 K. The triplet decay has a significantly different temperature dependence than that of singlets. From 295K to 80K, the triplet-triplet annihilation (TTA) rate decreases by two orders of magnitude, whereas the singlet-triplet annihilation rate decreases by <50% primarily a result of the different energy transfer mechanisms of singlets and triplets. The temperature dependence of TTA rate reveals two regimes separated by a transition at 180K from Marcus to MillerAbrahams transfer. This work deepens our understanding of exciton dynamics and energy transfer in small molecule organic materials.2

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“…In materials with significant disorder, charge transport is usually described in the framework of a hopping model in combination with, for instance, kinetic Monte Carlo (KMC) simulations, the concept of a transport level, effective-medium theory [6][7][8][9][10][11] , or percolation theory. [12][13][14][15][16][17][18] In the hopping regime, charge transport is governed by the thermally activated hopping of charge carriers within the manifold of localized states.…”

Section: Introductionmentioning

confidence: 99%

Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

2013

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We compare the merits of a hopping model and a mobility edge model in the description of the effect of charge-carrier concentration on the electrical conductivity, carrier mobility, and Fermi energy of organic semiconductors. We consider the case of a composite electronic density of states (DOS) that consists of a superposition of a Gaussian DOS and an exponential DOS. Using kinetic Monte Carlo simulations, we apply the two models in order to interpret the recent experimental data reported for n-doped C 60 films. While both models are capable of reproducing the experimental data very well and yield qualitatively similar characteristic parameters for the density of states, some discrepancies are found at the quantitative level.

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Diffusion and relaxation of energy in disordered organic and inorganic materials

Cited by 272 publications

References 27 publications

Role of Structural Order and Excess Energy on Ultrafast Free Charge Generation in Hybrid Polythiophene/Si Photovoltaics Probed in Real Time by Near-Infrared Broadband Transient Absorption

Role of Structural Order and Excess Energy on Ultrafast Free Charge Generation in Hybrid Polythiophene/Si Photovoltaics Probed in Real Time by Near-Infrared Broadband Transient Absorption

Temperature dependence of the exciton dynamics inDCM2:Alq3

Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

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