Thermal Evaporation versus Spin-Coating: Electrical Performance in Columnar Liquid Crystal OLEDs

Abstract

The electrical responses of a columnar liquid crystal (a diimidodiester derivative of benzo[ghi]perylene) deposited either by spin-coating or by thermal evaporation into a typical OLED device are compared. For the spin-coated film, homeotropic alignment was induced by thermal annealing, which enhanced the charge carrier mobility significantly. For the evaporated films, homeotropic alignment could not be obtained by annealing. However, a degree of rectification higher than 3 orders of magnitude was achieved, even without annealing, with an electrical response similar to the response of the aligned spin-coated film. A trap-limited space-charge-limited current model was used to extract the charge carrier mobility directly from the current-voltage curves. Grazing incidence wide-angle X-ray scattering confirmed the homeotropic alignment of the annealed spin-coated film, whereas the columns are mostly oriented parallel to the surface in the evaporated case. In a field-effect transistor with bottom-gate bottom-contact geometry, the evaporated film exhibited a typical behavior of an n-type transistor. The degree of intermolecular order is thereby strongly dependent on the deposition method where vacuum deposition leads to a higher order. This higher order, however, impedes reorientation by annealing of the evaporated film but leads to improved charge transport between the electrodes even without homeotropic alignment of columnar liquid crystal.

Pontos quânticos ambientalmente amigáveis: destaque para o óxido de zinco

“…104,105 A grande vantagem é que os cristais líquidos aliam a organização molecular dos sistemas cristalinos, necessária ao trânsito das cargas, à fluidez de um líquido, facilitando o processamento do material. Além disso, outra característica importante dos cristais líquidos é a resposta a estímulos externos, sendo possível modificar seu empacotamento e organização molecular, e com isso otimizar e controlar as suas propriedades condutoras.…”

Supramolecular complexes based on liquid‐crystalline polysiloxanes and copper phthalocyanine

“…Liquid crystals (LCs) are a fascinating class of soft materials due to their combined properties of fluidity and long‐range order. These materials possess orientational order without or with only low‐dimensional positional order . The combination of order and mobility in LCs is essential for achieving complex self‐organized structures or for yielding well‐organized materials that are able to respond to external stimuli .…”

“…These materials possess orientational order without or with only low-dimensional positional order. 1 The combination of order and mobility in LCs is essential for achieving complex self-organized structures or for yielding well-organized materials that are able to respond to external stimuli. 2 Liquid-crystalline polymers usually integrate good mechanical properties with viscoelastic behavior of the general macromolecule.…”

Electroluminescent and Optoelectronic Properties of OLEDs with Bay‐Extended, Distorted Perylene Esters as Emitter Materials

“…[36,37] Mainly compounds with differents ide chains, [38] heteroa toms [39] and functional groups [40] have been studied, but derivatives with extended arene cores have also garnered some attention. [41][42][43] Recently,p erylened erivatives containing helicene fragments in their cores have been of special interest owing to their peculiar properties, among otherss howing liquid crystalline behavior with minimal side chains due to distortions in the arene core. [44,45] The electronic and spectroscopic properties of extendedp erylened erivativesw ith distorted cores are also noteworthy.…”