TY  - JOUR
A1  - Salzmann, Ingo
A1  - Heimel, Georg
A1  - Duhm, Steffen
A1  - Oehzelt, Martin
A1  - Pingel, Patrick
A1  - George, Benjamin M.
A1  - Schnegg, Alexander
A1  - Lips, Klaus
A1  - Blum, Ralf-Peter
A1  - Vollmer, Antje
A1  - Koch, Norbert
T1  - Intermolecular hybridization governs molecular electrical doping
JF  - Physical review letters
N2  - Current models for molecular electrical doping of organic semiconductors are found to be at odds with other well-established concepts in that field, like polaron formation. Addressing these inconsistencies for prototypical systems, we present experimental and theoretical evidence for intermolecular hybridization of organic semiconductor and dopant frontier molecular orbitals. Common doping-related observations are attributed to this phenomenon, and controlling the degree of hybridization emerges as a strategy for overcoming the present limitations in the yield of doping-induced charge carriers.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevLett.108.035502
SN  - 0031-9007
VL  - 108
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Ghani, Fatemeh
A1  - Opitz, Andreas
A1  - Pingel, Patrick
A1  - Heimel, Georg
A1  - Salzmann, Ingo
A1  - Frisch, Johannes
A1  - Neher, Dieter
A1  - Tsami, Argiri
A1  - Scherf, Ullrich
A1  - Koch, Norbert
T1  - Charge Transfer in and Conductivity of Molecularly Doped Thiophene-Based Copolymers
JF  - Journal of polymer science : B, Polymer physics
N2  - The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design.
KW  - charge transfer
KW  - conducting polymers
KW  - doping
KW  - thiophene
Y1  - 2015
U6  - https://doi.org/10.1002/polb.23631
SN  - 0887-6266
SN  - 1099-0488
VL  - 53
IS  - 1
SP  - 58
EP  - 63
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Lange, Ilja
A1  - Reiter, Sina
A1  - Paetzel, Michael
A1  - Zykov, Anton
A1  - Nefedov, Alexei
A1  - Hildebrandt, Jana
A1  - Hecht, Stefan
A1  - Kowarik, Stefan
A1  - Woell, Christof
A1  - Heimel, Georg
A1  - Neher, Dieter
T1  - Tuning the work function of polar zinc oxide surfaces using modified phosphonic acid self-assembled monolayers
JF  - Advanced functional materials
N2  - Zinc oxide (ZnO) is regarded as a promising alternative material for transparent conductive electrodes in optoelectronic devices. However, ZnO suffers from poor chemical stability. ZnO also has a moderate work function (WF), which results in substantial charge injection barriers into common (organic) semiconductors that constitute the active layer in a device. Controlling and tuning the ZnO WF is therefore necessary but challenging. Here, a variety of phosphonic acid based self-assembled monolayers (SAMs) deposited on ZnO surfaces are investigated. It is demonstrated that they allow the tuning the WF over a wide range of more than 1.5 eV, thus enabling the use of ZnO as both the hole-injecting and electron-injecting contact. The modified ZnO surfaces are characterized using a number of complementary techniques, demonstrating that the preparation protocol yields dense, well-defined molecular monolayers.
KW  - ZnO
KW  - self-assembled monolayers
KW  - phosphonic acid
KW  - surface modification
KW  - electrodes
Y1  - 2014
U6  - https://doi.org/10.1002/adfm.201401493
SN  - 1616-301X
SN  - 1616-3028
VL  - 24
IS  - 44
SP  - 7014
EP  - 7024
PB  - Wiley-VCH
CY  - Weinheim
ER  -