TY  - JOUR
A1  - Goel, Mahima
A1  - Siegert, Marie
A1  - Krauss, Gert
A1  - Mohanraj, John
A1  - Hochgesang, Adrian
A1  - Heinrich, David C.
A1  - Fried, Martina
A1  - Pflaum, Jens
A1  - Thelakkat, Mukundan
T1  - HOMO–HOMO Electron Transfer: An Elegant Strategy for p‐Type Doping of Polymer Semiconductors toward Thermoelectric Applications
JF  - Advanced Materials
N2  - Unlike the conventional p‐doping of organic semiconductors (OSCs) using acceptors, here, an efficient doping concept for diketopyrrolopyrrole‐based polymer PDPP[T]\(_{2}\)‐EDOT (OSC‐1) is presented using an oxidized p‐type semiconductor, Spiro‐OMeTAD(TFSI)\(_{2}\) (OSC‐2), exploiting electron transfer from HOMO\(_{OSC-1}\) to HOMO\(_{OSC-2}\). A shift of work function toward the HOMO\(_{OSC-1}\) upon doping is confirmed by ultraviolet photoelectron spectroscopy (UPS). Detailed X‐ray photoelectron spectroscopy (XPS) and UV–vis–NIR absorption studies confirm HOMO\(_{OSC-1}\) to HOMO\(_{OSC-2}\) electron transfer. The reduction products of Spiro‐OMeTAD(TFSI)\(_{2}\) to Spiro‐OMeTAD(TFSI) and Spiro‐OMeTAD is also confirmed and their relative amounts in doped samples is determined. Mott–Schottky analysis shows two orders of magnitude increase in free charge carrier density and one order of magnitude increase in the charge carrier mobility. The conductivity increases considerably by four orders of magnitude to a maximum of 10 S m\(^{-1}\) for a very low doping ratio of 8 mol%. The doped polymer films exhibit high thermal and ambient stability resulting in a maximum power factor of 0.07 µW m\(^{-1}\) K\(^{-2}\) at a Seebeck coefficient of 140 µV K\(^{-1}\) for a very low doping ratio of 4 mol%. Also, the concept of HOMO\(_{OSC-1}\) to HOMO\(_{OSC-2}\) electron transfer is a highly efficient, stable and generic way to p‐dope other conjugated polymers.
KW  - molecular doping
KW  - Mott–Schottky analysis
KW  - organic semiconductors
KW  - polymer thermoelectrics
KW  - ultraviolet photoelectron spectroscopy
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-217850
VL  - 32
IS  - 43
ER  - 
TY  - JOUR
A1  - He, Tao
A1  - Stolte, Matthias
A1  - Burschka, Christian
A1  - Hansen, Nis Hauke
A1  - Musiol, Thomas
A1  - Kälblein, Daniel
A1  - Pflaum, Jens
A1  - Tao, Xutang
A1  - Brill, Jochen
A1  - Würthner, Frank
T1  - Single-crystal field-effect transistors of new Cl\(_{2}\)-NDI polymorph processed by sublimation in air
JF  - Nature Communications
N2  - Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (\(\beta\)-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (\(\alpha\)-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\alpha\)-phase) and up to 3.5 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\beta\)-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on \(\beta\)-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\). The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.
KW  - thin-film transistors
KW  - carrier transport
KW  - \(\beta\)-phase
KW  - organic semiconductors
KW  - induced phase transition
KW  - charge transport
KW  - materials design
KW  - \(\alpha\)-phase
KW  - mobility
KW  - pentacene
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149255
VL  - 6
IS  - 5954
ER  - 
TY  - JOUR
A1  - Sung, Jooyoung
A1  - Kim, Pyosang
A1  - Fimmel, Benjamin
A1  - Würthner, Frank
A1  - Kim, Dongho
T1  - Direct observation of ultrafast coherent exciton dynamics in helical π-stacks of self-assembled perylene bisimides
JF  - Nature Communications
N2  - Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with pi-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π-π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.
KW  - systems
KW  - molecules
KW  - J-aggregate behavior
KW  - absorption
KW  - spectroscopy
KW  - photoluminescence
KW  - diffusion
KW  - fluorescence
KW  - excimer formation
KW  - organic semiconductors
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148157
VL  - 6
IS  - 8646
ER  -