The effect of intermolecular interaction on excited states in p − DTS(FBTTH2)2

Reichenberger, Markus; Love, John A.; Rudnick, Alexander; Bagnich, S. A.; Panzer, Fabian; Stradomska, Anna; Bazan, Guillermo C.; Nguyen, Thuc‐Quyen; Köhler, Anna

doi:10.1063/1.4941700

Cited by 15 publications

(36 citation statements)

References 37 publications

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“…In the third time range, which is between 5.0 s and about 60 s, no further changes are observed. Based on earlier work, we associate the resulting thin film spectrum with a superposition of absorption from remaining disordered chains and aggregated chains . Evidently, there seems to be a critical concentration that facilitates aggregate formation as the solvent evaporates, consistent with calculations made for the poly( p ‐phenylene derivative) MEH‐PPV …”

Section: Resultssupporting

confidence: 78%

Controlling aggregate formation in conjugated polymers by spin‐coating below the critical temperature of the disorder–order transition

Reichenberger

Kroh

Matrone

et al. 2017

J Polym Sci B Polym Phys

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Aggregates -that is short-ranged ordered moieties in the solid-state of p-conjugated polymers -play an important role in the photophysics and performance of various optoelectronic devices. We have previously shown that many polymers change from a disordered to a more ordered conformation when cooling a solution below a characteristic critical temperature T c . Using in situ time-resolved absorption spectroscopy on the prototypical semiconducting polymers P3HT, PFO, PCPDTBT, and PCE11 (PffBT4T-2OD), we show that spincoating at a temperature below T c can enhance the formation of aggregates with strong intra-chain coupling. An analysis of their time-resolved spectra indicates that the formation of nuclei in the initial stages of film formation for substrates held below T c seems responsible for this. We observe that the growth rate of the aggregates is thermally activated with an energy of 310 meV, which is much more than that of the solvent viscosity (100 meV). From this we conclude that the rate controlling step is the planarization of a chain that is associated with its attachment to a nucleation center. The success of our approach for the rather dynamic deposition method of spin-coating holds promise for other solution-based deposition methods.So far, however, only limited approaches have been reported to induce aggregate formation in a controlled fashion, including slow solidification in marginal solvents, 26-29 control of entanglements and sonication, 30-34 and blending 35 -many using poly(3-hexyl thiophene) (P3HT) as model system and many relying on relatively time-consuming methodologies. Approaches to control the formation of aggregates during the solution deposition should ideally be based on considering thermodynamics of the solution as well as by taking the kinetics of film formation into account. 9 In particular with respect to the latter, several methods have been reported, such as varying the boiling point of the solvent, 9,21,36 varying Additional Supporting Information may be found in the online version of this article.

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Section: Resultssupporting

confidence: 78%

Controlling aggregate formation in conjugated polymers by spin‐coating below the critical temperature of the disorder–order transition

Reichenberger

Kroh

Matrone

et al. 2017

J Polym Sci B Polym Phys

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“…As there are multiple possibilities for both the conformation of the individual monomers and the actual stacking geometry, we cannot definitively select a single structure as being predominantly present in the experiment. However, the improved agreement for the dimer and trimer as compared to the monomer coupled with the prior work, 73 suggests such aggregates are present in our sample. Furthermore, the dimers and trimer maintain the spin density patterns shown in the monomers: no spin density on the silicon or germanium, no spin density on the alkyl substituents on the thiophenes or metals, but spin density on the fluorine atoms.…”

Section: Resultssupporting

confidence: 52%

Charge Separation and Triplet Exciton Formation Pathways in Small-Molecule Solar Cells as Studied by Time-Resolved EPR Spectroscopy

et al. 2017

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Organic solar cells are a promising renewable energy technology, offering the advantages of mechanical flexibility and solution processability. An understanding of the electronic excited states and charge separation pathways in these systems is crucial if efficiencies are to be further improved. Here we use light induced electron paramagnetic resonance (LEPR) spectroscopy and density functional theory calculations (DFT) to study the electronic excited states, charge transfer (CT) dynamics and triplet exciton formation pathways in blends of the small molecule donors (DTS(FBTTh2)2, DTS(F2BTTh2)2, DTS(PTTh2)2, DTG(FBTTh2)2 and DTG(F2BTTh2)2) with the fullerene derivative PC61BM. Using high frequency EPR the g-tensor of the positive polaron on the donor molecules was determined. The experimental results are compared with DFT calculations which reveal that the spin density of the polaron is distributed over a dimer or trimer. Time-resolved EPR (TR-EPR) spectra attributed to singlet CT states were identified and the polarization patterns revealed similar charge separation dynamics in the four fluorobenzothiadiazole donors, while charge separation in the DTS(PTTh2)2 blend is slower. Using TR-EPR we also investigated the triplet exciton formation pathways in the blend. The polarization patterns reveal that the excitons originate from both intersystem crossing (ISC) and back electron transfer (BET) processes. The DTS(PTTh2)2 blend was found to contain substantially more triplet excitons formed by BET than the fluorobenzothiadiazole blends. The higher BET triplet exciton population in the DTS(PTTh2)2 blend is in accordance with the slower charge separation dynamics observed in this blend.

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“…In summary, the cooling induced order–disorder transition of P3HT proceeds in three steps: (1) planarization of random chains; (2) collapse of planarized chains into disordered aggregate; (3) planarization of aggregate. Moreover, the general cooling induced order–disorder transition has been demonstrated in a wide range of organic semiconductors, including PCPDTBT, DTS(FBTTH 2 ) 2 , at varying transition temperatures [58, 64, 65] . With further decreased temperature, the partial side chain crystallization happens after the interchain stacking, which can be evidenced with small‐angle and wide‐angle X‐ray scattering characterizations [36, 66] .…”

Section: Temperature Induced Aggregation In Solutionmentioning

confidence: 95%

Temperature Induced Aggregation of Organic Semiconductors

Yan

et al. 2020

Chemistry A European J

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One important feature of organic semiconductors is their solution processability, which allows researchers to tune their aggregation states in solution and solid states and to control the processing conditions to reach desirable electronic and optoelectronic properties. Temperature is one of the most important processing parameters of organic semiconductors and has been studied extensively particularly for those conjugated small‐ and macro‐ molecules with strong temperature‐dependent aggregation properties. This minireview summarizes the temperature‐induced aggregation behaviors of organic semiconductors in solution, during solution casting and upon thermal annealing post‐treatment of solid‐state thin films. The influences of different aggregation states on the optoelectronic properties, in particular the photovoltaic properties, are discussed. The conclusions in this work will provide a rational guide to precisely control the aggregation states of organic semiconductors to fabricate high‐performance optoelectronic devices.

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The effect of intermolecular interaction on excited states in p − DTS(FBTTH2)2

Cited by 15 publications

References 37 publications

Controlling aggregate formation in conjugated polymers by spin‐coating below the critical temperature of the disorder–order transition

Controlling aggregate formation in conjugated polymers by spin‐coating below the critical temperature of the disorder–order transition

Charge Separation and Triplet Exciton Formation Pathways in Small-Molecule Solar Cells as Studied by Time-Resolved EPR Spectroscopy

Temperature Induced Aggregation of Organic Semiconductors

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