Intensity-dependent relaxation dynamics and the nature of the excited-state species in solid-state conducting polymers

Maniloff, Eric S.; Klimov, Victor I.; McBranch, D.

doi:10.1103/physrevb.56.1876

Cited by 86 publications

(81 citation statements)

References 29 publications

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“…44 The 625 nm SE data at the same excitation fluences are shown in Figure 7 (b) (same data as in Figure 6 (a) but scaled to the same value at time zero). The change in PA dynamics at early times with intensity is in agreement with the ideas of McBranch and co-workers that a portion of the PA results from the byproducts of E-EA [40][41][42] or of excitonic interactions with intrinsic defects. 44 What is also clear from the figure, however, is that the PA and SE dynamics do not agree with each other, even at low intensities.…”

Section: Role Of Film Morphology In Exciton-exciton Annihilationsupporting

confidence: 90%

“…These results are in accord with previous work on exciton-exciton (bimolecular) annihilation. 40,41,[43][44][45][48][49][50] The increasing SE decay rate with increasing excitation density also resembles that expected from amplified spontaneous emission. 69,71,73 The data presented here, however, used excitation fluences nearly 2 orders of magnitude lower than those previously reported for the observation of line narrowing in MEH-PPV films.…”

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 89%

“…[40][41][42] At low excitation intensities, these workers found identical SE and PA dynamics, suggesting that only a single, intrachain species is needed to explain the photophysics. At higher intensities, a new PA band appeared whose magnitude increased quadratically with intensity.…”

Section: Introductionmentioning

confidence: 94%

“…94 Equation 2 has no analytic solution and thus must be fit to the data numerically. While most workers have chosen either eq 2 or eq 3 to model their data, both McBranch and co-workers 41 and Dogariu et al 45 have considered both models in the analysis of their results. McBranch and co-workers found that eq 2 provided a much more satisfactory fit to the data than did eq 3.…”

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 99%

“…McBranch and co-workers found that eq 2 provided a much more satisfactory fit to the data than did eq 3. 41 Dogariu et al transformed their data in such a way as to allow the functional form of the timedependent coefficient in front of the quadratic term in the model to be determined without assuming the form of either eq 2 or eq 3. In agreement with McBranch and co-workers, they found that a 1/ t term like that in eq 2 provided the best fit to the experimental data.…”

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 99%

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Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

et al. 1999

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The presence of interchain species in the photophysics of conjugated polymer films has been the subject of a great deal of controversy. In this paper, we present strong evidence that interchain species do form in conjugated polymer films, and that the degree of interchain interactions can be controlled by varying the solvent and polymer concentration of the solution from which the films are cast. Thus, much of the controversy in the literature can be resolved by noting that the polymer samples in different studies had different side groups or were prepared in different ways and thus have different degrees of interchain interaction. The photoluminescence (PL) of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene), MEH-PPV, changes both its spectral shape and quantum yield when the films are prepared from different solutions or when the morphology is varied by annealing. Increasing the amount of interchain interactions enhances the red portion of the film's PL, a result assigned to a combination of changes in the vibronic structure of the PL of the exciton and increased numbers of weakly emissive interchain species. Photoluminescence excitation spectroscopy shows that excitation to the red edge of the absorption band preferentially enhances the red emission, suggesting that the interchain species are aggregates with a distinct ground state absorption. Scanning force microscopy shows topographic features that correlate with the degree of interchain interactions, verifying that the morphology of conjugated polymer films changes with polymer concentration, choice of solvent, and spin-casting speed. Even at low excitation intensities, photooxidative damage occurs quickly in MEH-PPV films excited in air, and the rate at which damage occurs is sensitive to the packing of the polymer chains. For samples under vacuum at low excitation intensity, a long-lived emissive tail, in combination with excitedstate absorption dynamics that do not match those of the emissive species, provide direct evidence for the production of interchain aggregates. Annealing an MEH-PPV film produces a photophysical signature similar to photooxidation, implying that defects in conjugated polymer films are intrinsic and depend on the details of how the chains are packed. At higher excitation intensities, we find that exciton-exciton annihilation occurs, and that the probability for annihilation can vary by an order of magnitude depending on the degree of interchain contact in the film. Finally, we show that changing the film morphology has a direct effect on the performance of MEH-PPV-based light-emitting diodes. Higher degrees of interchain interaction enhance the mobility of carriers at the expense of lower quantum efficiencies for electroluminescence. Taken together, the results reconcile much of the contradictory literature and provide a prescription for the optimization of conjugated polymer films for particular device applications.

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Section: Role Of Film Morphology In Exciton-exciton Annihilationsupporting

confidence: 90%

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 94%

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 99%

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 99%

See 3 more Smart Citations

Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

et al. 1999

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Interaction Range for Photoexcitations in Luminescent Conjugated Polymers

Vacar¹,

Dogariu

Heeger

1998

Adv. Mater.

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on the structure in the c-direction has not been obtained yet. The diameter of a PW 11 O 39 7± anion is assumed to be 1.09 nm, which is the same as that of a PW 12 O 40 3± Keggin anion. [14] The unit cell has 5 PW 11 O 39 7± anions, 30 C 12 TMA + cations, and 5 Na + cations. The expected pore diameter and wall thickness calculated from this model are 2.76 and 1.09 nm, respectively.In summary, a hexagonally ordered mesostructured material constructed with lacunar heteropoly anions and surfactant cations, WP, was synthesized by hydrothermal reaction of Na 2 WO 4 ×2H 2 O with H 3 PO 4 and C 12 H 25 N(CH 3 ) 3 Br at 403 K for 6 h. The chemical formula of WP obtained was [CH 3 (CH 2 ) 11 N(CH 3 ) 3 ] 6 NaPW 11 O 39 ×5.7H 2 O and a hexagonal superstructural model of the WP was proposed. Although heteropoly acids with a large pore structure have been of interest in catalysts and proton conductors with high performance, at present, the hexagonal structure of WP collapsed upon calcination. [15] Experimental The solution of surfactant and phosphate was prepared by dissolving 6.17 g of C 12 H 25 N(CH 3 ) 3 Br and 10 mL of 1 M H 3 PO 4 in 20 mL of deionized water. Subsequently 6.60 g of Na 2 WO 4 ×2H 2 O was added to the solution with vigorous stirring. Immediately a white gel precipitated. The molar composition of the resulting mixture was 1.0 Na 2 WO 4 ×2H 2 O : 0.5 H 3 PO 4 : 1.0 C 12 H 25 N(CH 3 ) 3 Br : 83.3 H 2 O. After being stirred at room temperature for 1 h, the mixture (ca. pH 8.3) was placed in a 40 mL Teflon bottle mounted in an autoclave and hydrothermally treated at 403 K for 6 h. The white solid product obtained (denoted by WP) was filtered, washed with deionized water, and dried at 353 K for 6 h. (NH 4 ) 3 PW 12 O 40 ×3H 2 O (PW 12 ) was purchased from Wako Pure Chemical Co. and Na 7 PW 11 O 39 ×nH 2 O (PW 11 ) and Na 8 HPW 9 O 34 ×nH 2 O (PW 9 ) were prepared according to the literature [9,16].

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Key Tradeoffs Limiting the Performance of Organic Photovoltaics

Ramírez

Causa

Zhong

et al. 2018

Advanced Energy Materials

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perspective on the physics underlying the conventional and new systems and their performance limits.The discussion is focused on two key issues, which have for long hindered OPV performances, and their applicability to the new systems. The first is a charge generation-open-circuit voltage (V oc ) tradeoff, which has typically meant a driving force is required for charge transfer. Consequently, high-performance devices have exhibited either a high short-circuit current J sc or a high V oc . [1] The second is that the slow charge extraction and fast recombination mean the optimum device performance is obtained at active layer thicknesses inferior to those required for full absorption. This is manifested in a tradeoff between absorption and fill factor (FF). We first provide a modern outlook on the physics behind these tradeoffs. Both the fundamentals and their application to OPV systems are covered. We introduce the thermodynamics of photovoltaic conversion, which are currently the most powerful tool to describe the V oc of OPVs. We cover the various theories behind charge generation and, to widen the debate, their implications on devices and especially their V oc .This leads us to consider the recent small molecule systems and the exciting possibilities for experimental insights they offer. Some of these systems show record values for their emission yield and very low charge generation-V oc tradeoffs. Also, the role of nonradiative recombination due to molecular vibrations is receiving increasing attention. We examine the role of the tradeoffs in limiting NFA performance and suggest potential explanations for their improved performance as well as some promising avenues for research.

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Intensity-dependent relaxation dynamics and the nature of the excited-state species in solid-state conducting polymers

Cited by 86 publications

References 29 publications

Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

Interaction Range for Photoexcitations in Luminescent Conjugated Polymers

Key Tradeoffs Limiting the Performance of Organic Photovoltaics

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