TY  - JOUR
A1  - Scharsich, Christina
A1  - Lohwasser, Ruth H.
A1  - Sommer, Michael
A1  - Asawapirom, Udom
A1  - Scherf, Ullrich
A1  - Thelakkat, Mukundan
A1  - Neher, Dieter
A1  - Koehler, Anna
T1  - Control of aggregate formation in poly(3-hexylthiophene) by solvent, molecular weight, and synthetic method
JF  - Journal of polymer science : B, Polymer physics
N2  - Aggregate formation in poly(3-hexylthiophene) depends on molecular weight, solvent, and synthetic method. The interplay of these parameters thus largely controls device performance. In order to obtain a quantitative understanding on how these factors control the resulting electronic properties of P3HT, we measured absorption in solution and in thin films as well as the resulting field effect mobility in transistors. By a detailed analysis of the absorption spectra, we deduce the fraction of aggregates formed, the excitonic coupling within the aggregates, and the conjugation length within the aggregates, all as a function of solvent quality for molecular weights from 5 to 19 kDa. From this, we infer in which structure the aggregated chains pack. Although the 5 kDa samples form straight chains, the 11 and 19 kDa chains are kinked or folded, with conjugation lengths that increase as the solvent quality reduces. There is a maximum fraction of aggregated chains (about 55 +/- 5%) that can be obtained, even for poor solvent quality. We show that inducing aggregation in solution leads to control of aggregate properties in thin films. As expected, the field-effect mobility correlates with the propensity to aggregation. Correspondingly, we find that a well-defined synthetic approach, tailored to give a narrow molecular weight distribution, is needed to obtain high field effect mobilities of up to 0.01 cm2/Vs for low molecular weight samples (=11 kDa), while the influence of synthetic method is negligible for samples of higher molecular weight, if low molecular weight fractions are removed by extraction.
KW  - conformational analysis
KW  - conjugated polymers
KW  - crystallization
KW  - films
KW  - interaction parameter
KW  - molecular weight distribution
KW  - molar mass distribution
KW  - nucleation
KW  - photophysics
KW  - structure
KW  - UV-vis spectroscopy
Y1  - 2012
U6  - https://doi.org/10.1002/polb.23022
SN  - 0887-6266
VL  - 50
IS  - 6
SP  - 442
EP  - 453
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Salert, Beatrice Ch. D.
A1  - Krueger, Hartmut
A1  - Bagnich, Sergey A.
A1  - Unger, Thomas
A1  - Jaiser, Frank
A1  - Al-Sa'di, Mahmoud
A1  - Neher, Dieter
A1  - Hayer, Anna
A1  - Eberle, Thomas
T1  - New polymer matrix system for phosphorescent organic light-emitting diodes and the role of the small molecular co-host
JF  - Journal of polymer science : A, Polymer chemistry
N2  - A new matrix system for phosphorescent organic light-emitting diodes (OLEDs) based on an electron transporting component attached to an inert polymer backbone, an electronically neutral co-host, and a phosphorescent dye that serves as both emitter and hole conductor are presented. The inert co-host is used either as small molecules or covalently connected to the same chain as the electron-transporting host. The use of a small molecular inert co-host in the active layer is shown to be highly advantageous in comparison to a purely polymeric matrix bearing the same functionalities. Analysis of the dye phosphorescence decay in pure polymer, small molecular co-host film, and their blend lets to conclude that dye molecules distribute mostly in the small molecular co-host phase, where the co-host prevents agglomeration and self-quenching of the phosphorescence as well as energy transfer to the electron transporting units. In addition, the co-host accumulates at the anode interface where it acts as electron blocking layer and improves hole injection. This favorable phase separation between polymeric and small molecular components results in devices with efficiencies of about 47 cd/A at a luminance of 1000 cd/m(2). Investigation of OLED degradation demonstrates the presence of two time regimes: one fast component that leads to a strong decrease at short times followed by a slower decrease at longer times. Unlike the long time degradation, the efficiency loss that occurs at short times is reversible and can be recovered by annealing of the device at 180 degrees C. We also show that the long-time degradation must be related to a change of the optical and electrical bulk properties.
KW  - charge transport
KW  - conducting polymer
KW  - degradation
KW  - host-guest systems
KW  - light-emitting diodes
KW  - random copolymer
KW  - synthesis
KW  - UV-vis spectroscopy
Y1  - 2013
U6  - https://doi.org/10.1002/pola.26409
SN  - 0887-624X
VL  - 51
IS  - 3
SP  - 601
EP  - 613
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -