Improved Intrapixel Thickness Uniformity of Slot-Coated PEDOT:PSS Films for OLEDs via Dilution and Predrying Treatments

Due to capillary force, solution coating of pristine poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) solution in the presence of banks exhibits poor intrapixel thickness uniformity, shrinking the emission area of organic light-emitting diodes (OLEDs) within pixels. To enhance i...

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Bibliographic Details
Published in:IEEE transactions on electron devices 2018-10, Vol.65 (10), p.4506-4512
Main Authors: Shin, Dong-Kyun, Lee, Jinyoung, Kim, Gieun, Park, Jongwoon
Format: Article
Language:English
Subjects:
4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS
Aqueous poly
Capillary flow
Coatings
Conduction heating
Conductive heat transfer
Convective flow
Deionization
Dilution
Diodes
Emission
Evaporation rate
Flow velocity
Heating systems
intrapixel thickness uniformity
Morphology
Organic light emitting diodes
organic light-emitting diode (OLED)
Pixels
predrying treatments
slot coating
Solvents
Spin coating
Surface morphology
Thickness measurement
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Summary:Due to capillary force, solution coating of pristine poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) solution in the presence of banks exhibits poor intrapixel thickness uniformity, shrinking the emission area of organic light-emitting diodes (OLEDs) within pixels. To enhance it, we have applied the predrying treatments (predrying under atmospheric pressure, by heat conduction, and under vacuum) to wet films. However, its impact is minimal because the evaporation rate of wet films is not well-matched to the capillary flow rate of solute during the predrying process. It is tackled by diluting the pristine PEDOT:PSS solution with deionized water such that the evaporation of wet films is retarded and in turn, the convective flow of solute occurs from the pixel edge to the center. With increasing dilution, a noticeable enhancement in its intrapixel thickness uniformity is observed without any sacrifice on the surface morphology. It is found that the predrying effect by heat conduction is more pronounced than that under vacuum. Furthermore, we have demonstrated that slot-die coating rather than spin coating is preferable in the coating of diluted PEDOT:PSS solutions. With the diluted solution and predrying by heat conduction, the thickness uniformity can be enhanced by a factor of 2 and the emission area of OLEDs within pixels is broadened to a great extent.
ISSN:0018-9383
1557-9646
DOI:10.1109/TED.2018.2866693