News from Nanotechjapan


Brush Printing Creates Polarized Green Fluorescence ---OLED's Fabricated from an Oriented Polymer Film---

 Hiroshima University announced on September 28, 2020, that a research group led by Professor Ken-ichi Saitow at Natural Science Center for Basic Research and Development (N-BARD), and Graduate School of Advanced Science and Engineering at the university succeeded in preparing a uniaxially ori-ented film of green light-emitting conductive polymer by brush-printing. This work was supported by Funding Program for Next Generation World-Leading Researchers (NEXT Program) of Cabinet Office (CAO) and details were published in ACS Applied Materials and Interfaces*.

 Most of the organic optoelectronic devices are operated with the molecules orienting in a fixed direc-tion. Rotation of oriented liquid crystal molecules controls polarized light transmission. Deposition with followed rubbing treatment of alignment film is an important process for the device fabrication.  Here, the research group proposed brush printing, similar to drawing a picture by a brush soaked with color-ing liquid to make an oriented film.

 A solution of a green light-emitting conductive polymer, poly (9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) was used to paint some patterns on the glass substrate by a brush and dried. Several samples of different brushing speed and thickness were prepared for characterization by optical microscopy and spectroscopy. The fluorescence polarization ratio of the oriented F8BT films was as high as 11.3, and the average orientation factor reached 0.74 ± 0.06. Green fluorescence at ~550nm was excited by blue light at ~480nm. 3D mapping (fluorescence, Raman spectra and thickness) revealed that polarized green fluorescence originates from polymer chains uniaxially oriented along the brush direction. The high ori-entation was available for a film thickness < 100nm at optimum brushing speed. This brush-printing method can be applied to the fabrication of optoelectronic devices. Polarized green electroluminescence was preliminarily demonstrated by the OLED assembled from an oriented F8BT film.

*Toshiki Sakata, Daisuke Kajiya, and Ken-ichi Saitow, "Brush Printing Creates Polarized Green Fluo-rescence: 3D Orientation Mapping and Stochastic Analysis of Conductive Polymer Films", ACS Applied Materials and Interfaces 2020, DOI: 10.1021/acsami.0c08061; Publication Date: September 28, 2020