The document discusses the electrical response of columnar liquid crystals used in diode structures, highlighting their unique molecular order and charge transport properties. It reports significant findings, including a four orders of magnitude increase in current and five in charge carrier mobility due to thermal annealing, which achieved homeotropic alignment. The results indicate that molecular orientation can be effectively manipulated to enhance the electro-optical properties of devices.

1. 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: juh_19@yahoo.com.br

2. 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

3. 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. 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.

5. 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
Heat Flow
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. 6
 Spin-coating thin film:
 Thermal annealing: device at 120 ºC
 Polarizing optical microscopy:
 Homeotropic alignment:
face-on
(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).

7. 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. 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. 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 60
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
Applied Voltage (V)
After
During
Before
Mobility (cm
2
/Vs)
Published in: J. Eccher et al. ACS
Appl. Mater. Interfaces, 5, 11935-
11943 (2013).

10. CONCLUSIONS
10
 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.

11. 10th Ibero-American Workshop on Complex Fluids FLORIANÓPOLIS - SANTA CATARINA - BRAZIL 25-29 October 2015
11
Chairman:
Prof. Ivan H. Bechtold
Prof. Hugo Gallardo Website: http://10ibero.paginas.ufsc.br/

12. 12 Thanks for attention!!!
Financial Supports:
Acknowledgments: