electrical response of a columnar liquid crystal applied in a diode structure
DESCRIPTION
Apresentação do trabalho que ganhou o Prêmio Bernhard Gross ao melhor oral do XIII Encontro da SBPMat.TRANSCRIPT
Electrical response of a columnar liquid crystal applied
in a diode structure Juliana Eccher1, Gregório C. Faria2, Harald Bock3, Heinz von Seggern4,
Wojciech Pisula5, Wojciech Zajaczkowski5, Ivan H. Bechtold1.
UNIVERSIDADE FEDERAL DE SANTA CATARINA
XIII Brazilian Materials Research Society Meeting
1Universidade Federal de Santa Catarina, Departamento de Física, SC, Brasil. 2Universidade de São Paulo, Instituto de Física de São Carlos, SP, Brasil. 3University of Bordeaux, Centre de Recherche Paul-Pascal, CNRS , France. 4 Technical University of Darmstadt, Department of Electronic Materials,
Germany. 5Max-Planck-Institut for Polymer Research, Mainz, Germany.
João Pessoa, September, 2014.
Laboratório de Optoeletrônica Orgânica
e Sistemas Anisotrópicos e-mail: [email protected]
Liquid Crystals (LCs)
molecular order + fluidity (charge transport) (easy processability)
anisometric organic molecules rod-shape disk-shape
Crystal
Smetic A
Smetic C
Nematic Isotropic
Liquid
Temperature
Liquid-crystalline mesophases
2
Discotic Liquid Crystals
Hexagonal columnar mesophase (Colh):
Synthesis: Dr. Harald Bock, CRPP, France. Colh at room temperature. n-type semiconductor. µ > 1 cm2/Vs.
Material:
benzo[ghi]perylene-diimidodiester
3
Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5,
11935-11943 (2013).
4
Orientation of the Columnar LCs
Edge-on Orientation (Planar Alignment)
Face-on Orientation (Homeotropic Alignment)
Transistor Diode
Advantage:
Modify the molecular orientation to control and improve the electro-optical properties of the devices (thermal annealing, surface treatments, electric and magnetic fields);
The mobility (µ) is highly dependent on the intracolunar alignment.
Results:
-60 -30 0 30 60 90 120 150 180
H = 9.1 kJ/mol
H = 8.8 kJ/mol
148.2 0C
Colh Iso
Iso
heating
Colh
He
at F
low
Temperature (oC)
cooling
153.4 0C
120 ºC
25 ºC
Polarizing optical microscopy
cooling: Iso 148.2ºC Colh
5
DSC (Differential Scanning Calorimetry)
Published in: J. Eccher et al. ACS Appl. Mater.
Interfaces, 5, 11935-11943 (2013).
6
Spin-coating thin film:
Thermal annealing:
device at 120 ºC
Polarizing optical microscopy:
Homeotropic alignment: face-on
(b
)
(c) (d)
(a) (b)
(e) (f)
face-on
3h
0h 0h
1h
3h
1h (c)
Published in: J. Eccher et al. ACS Appl.
Mater. Interfaces, 5, 11935-11943
(2013).
Charge Carrier Mobility from J-V Curves
7
: Poole-Frenkel coefficient Boundary condition: E (0) = 0
Published in: J. Eccher et al. ACS Appl. Mater.
Interfaces, 5, 11935-11943 (2013).
8
J-V and Luminance-Voltage Characteristics
spin-coating film
Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935-11943 (2013).
9
Charge Carrier Mobility from J-V Curves
Parameter Before During After
µ0 (cm2/Vs) 9.86 × 10-10 9.12 × 10-10 9.03 × 10-10
(cm/V) 1/2 0.44 × 10-2 1.98 × 10-2 2.11 × 10-2
µ at +15 V (cm2/Vs)
8.8 × 10-8 4.5 × 10-4 8.5 × 10-3
Mobility 5 orders of magnitude higher after alignment.
0 10 20 30 40 50 6010
-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
Applied Voltage (V)
After
During
Before
Mo
bili
ty (
cm
2/V
s)
Published in: J. Eccher et al. ACS
Appl. Mater. Interfaces, 5, 11935-
11943 (2013).
CONCLUSIONS
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Spin-coating film: The annealing process resulted in the homeotropic alignment. A gain of 4 orders of magnitude in current and 5 orders of magnitude in charge carrier mobility was surprisingly obtained. The electroluminescence was also improved dramatically.
Evaporated film: Homeotropic alignment was not observed. A high rectification degree was obtained even before annealing, indicating that the molecular packing in the evaporated film is more ordered and compact than in the spin-coated film before annealing.
10th Ibero-American Workshop on
Complex Fluids
FLORIANÓPOLIS - SANTA CATARINA - BRAZIL
25-29 October 2015
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Chairman:
Prof. Ivan H. Bechtold
Prof. Hugo Gallardo
Website:
http://10ibero.paginas.ufsc.br/
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Thanks for attention!!!
Financial Supports:
Acknowledgments: