Characterization of donor and acceptor discotic liquid crystals to

apply in organic devices

Simone V Bernardino(2), Juliana Eccher(2), Marli Ferreira(2,3),Deise M. P. O. Santos(2,3),

Harald Bock(3), Ivan H. Bechtold(2), Marta E. R. Dotto(1)

(1,2)Physics Department - Universidade Federal de Santa Catarina, Florianópolis,

Brasil

+554837212867and martaelisa.rd@ufsc.brl

2Chemistry Department - Universidade Federal de Santa Catarina, Florianópolis,

Brasil 3Centre de Recherche Paul-Pascal, CNRS - University of Bordeaux, France.

1. Introduction – The field of electronic organic devices has grown enormously in recent years, where

great progress have been made in various fields of science and the challenges facing the use of these

devices are great. One of the organic materials that have attracted much attention from researchers are

liquid crystals. Among the promising organic materials, discotic liquid crystals (DLCs) stand out as self-

organized semiconductors, exhibiting high charge carrier mobility, long exciton diffusion length and wide

absorption range over the solar spectrum.

2. Experimental - In this work as active layers were used combinations of two DLCs perylene derivative

(one as electron donor and the other as electron acceptor) materials. The thin films were produced by

spin-coating and characterized by MOLP, DSC) and X-Ray diffraction to obtain information about

thermotropic behavior. The photophysical properties were analyzed by UV-Vis and fluorescence

spectroscopy and morphological characteristic and roughness of surface were investigated by AFM and,

also the electron mobility was obtained by time of flight (TOF) technique. Also electrical properties were

investigated in the diode structure.

3. Results and Discussion - In the optical and morphological analysis of the CLs after another thermal

treatment, in three different thicknesses, the compounds M1[1] and D2 [2] presented a distinct behavior,

however both presented an homogeneous, flat and smooth texture morphology. The mobility of the liquid

crystalline materials were studied in three structures: ITO/PEDOT:PSS/CL/Au, to determine the mobility

of holes; Al/CL/Al structure to determine electron mobility and ITO/PEDOT:PSS/CL/Al to determine the

effective mobility of the device. The mobility was measured from the application of a theoretical model to

the experimental curves of current density as a function of the applied potential.

4. Conclusions - By DSC, MOLP and XRD measurements showed that thermal stability of Colhex

mesophase until room temperature was preserved. The compounds presented absorbance and emission in

the UV-Vis through optical characterization.The Excited state lifetime measurements revealed that the

mixture of materials the emission of M1 is higher in solution than film related to energy transfer. The LCs

presented granular domains and low roughness ~ 10 nm through AFM characterization. Mobility values

showed best combination: M1 (any thickness) with D2 (20 nm) are good candidate to apply in OPVs.

5. References

[1] Ferreira, M., et al., Columnar Liquid‐Crystalline Dinaphthoperylenetetracarboxdiimides. Chemistry–

A European Journal, 2015. 21(11): p. 4391-4397.

[2] Pereira de Oliveira Santos, D.M., et al., Stabilization of the Columnar Mesophase of Perylenediimide

by Racemic Triple Tails. Chemistry–A European Journal, 2016. 22(22): p. 7389-7393.

M&Ns-19, Paris, 17-19 Pag 9M&Ns-19, Paris, 17-19 July 2019