TY  - JOUR
A1  - Koopman, Wouter-Willem Adriaan
A1  - Natali, Marco
A1  - Bettini, Cristian
A1  - Melucci, Manuela
A1  - Muccini, Michele
A1  - Toffanin, Stefano
T1  - Contact Resistance in Ambipolar Organic Field-Effect Transistors Measured by Confocal Photoluminescence Electro-Modulation Microscopy
JF  - ACS applied materials & interfaces
N2  - Although it is theoretically expected that all organic semiconductors support ambipolar charge transport, most organic transistors either transport holes or electrons effectively. Single-layer ambipolar organic field-effect transistors enable the investigation of different mechanisms in hole and electron transport in a single device since the device architecture provides a controllable planar pn-junction within the transistor channel. However, a direct comparison of the injection barriers and of the channel conductivities between electrons and holes within the same device cannot be measured by standard electrical characterization. This article introduces a novel approach for determining threshold gate voltages for the onset of the ambipolar regime from the position of the pn-junction observed by photoluminescence electromodulation (PLEM) microscopy. Indeed, the threshold gate voltage in the ambipolar bias regime considers a vanishing channel length, thus correlating the contact resistance. PLEM microscopy is a valuable tool to directly compare the contact and channel resistances for both carrier types in the same device. The reported results demonstrate that designing the metal/organic semiconductor interfaces by aligning the bulk metal Fermi levels to the highest occupied molecular orbital or lowest unoccupied molecular orbital levels of the organic semiconductors is a too simplistic approach for optimizing the charge injection process in organic field-effect devices.
KW  - electro-modulation microscopy
KW  - organic field-effect transistors
KW  - threshold voltages
KW  - contact resistance
KW  - photoluminescence
Y1  - 2018
U6  - https://doi.org/10.1021/acsami.8b05518
SN  - 1944-8244
VL  - 10
IS  - 41
SP  - 35411
EP  - 35419
PB  - American Chemical Society
CY  - Washington
ER  -