[논문]Polymer Dispersed Liquid Crystal for Enhanced Light Out-Coupling Efficiency of Organic Light Emitting Diodes

Gasonoo, Akpeko; Ahn, Hyeon-Sik; Lee, Jonghee; Kim, Min-Hoi; Lee, Jae-Hyun; Choi, Yoonseuk

doi:10.7471/ikeee.2020.24.1.140

Polymer Dispersed Liquid Crystal for Enhanced Light Out-Coupling Efficiency of Organic Light Emitting Diodes 원문보기

전기전자학회논문지 = Journal of IKEEE, v.24 no.1, 2020년, pp.140 - 146

Gasonoo, Akpeko (Department of Electronic Engineering, Hanbat National University) , Ahn, Hyeon-Sik (Department of Electronic Engineering, Hanbat National University) , Lee, Jonghee (Department of Creative Convergence Engineering, Hanbat National University) , Kim, Min-Hoi (Department of Creative Convergence Engineering, Hanbat National University) , Lee, Jae-Hyun (Department of Creative Convergence Engineering, Hanbat National University) , Choi, Yoonseuk (Department of Electronic Engineering, Hanbat National University)

Abstract ▼ AI-Helper

We investigated light extraction film based on polymer dispersed liquid crystal (PDLC) for application in organic light emitting diodes (OLEDs). At least 30 seconds of direct UV irradiation process for curing PDLC film on a bottom-emitting OLEDs was successfully achieved without damage on the intrinsic properties of the OLED. We demonstrated that high haze and transmittance can be tuned simultaneously by controlling the UV curing time. By adding PDLC as an external layer without any additional treatment, the light scattering and extraction is increased. Consequently, a PDLC scattering film with 89.8% and 59.9 of total transmittance and haze respectively, achieved about 16% of light intensity enhancement from integrating sphere measurement.

주제어

표/그림 (5)

그림 Fig. 1. Fabrication process of PDLC scattering film.
그림 Fig. 2. Optical microscopic images of PDLC scattering films on bare glass substrate cured at (a) 25 s (b) 30 s and (b) 40 s, respectively.
표 Table 1. Optical characteristics of PDLC scattering film.
그림 Fig. 4. The current density-voltage-luminance (J-V-L) characteristics of OLED devices with (red circle) and without (black square) scattering film.
그림 Fig. 5. EL spectrum of OLEDs with (red circle) and without (black square) the PDLC scattering film (cured at 30 s).

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제안 방법

First, optical analysis was done to elucidate the optical characteristics of the PDLC films. Figure 2 shows the optical microscopic images of PDLC films prepared with different curing times at room temperature with a 4 W ultraviolet (UV) source (350 μW/cm² at wavelength of 365 nm).
In this study, we adopt polymer dispersed liquid crystal (PDLC) film as a light scattering and extraction layer for enhancing the out-coupling efficiency of OLEDs. Thin PDLC films have been developed for a wide range of photonic applications in recent years [20-21].
In this study, we investigated PDLC films as light extraction layers and their application in enhancing the out-coupling efficiency of OLEDs. Uniform and transparent composite film was successively fabricated with UV curable prepolymer and nematic LC in a proportionate concentration.
Transmission measurements to determine the light extraction of the PDLC scattering film were conducted and analyzed using a UV-vis-NIR spectrophotometer (Perkinelmer Lambda 950) in the wavelength range of 380～800 nm. Table 1 shows the optical characteristics of PDLC scattering film for films cured at 30 s and 40 s respectively.

대상 데이터

Figure 2 shows the optical microscopic images of PDLC films prepared with different curing times at room temperature with a 4 W ultraviolet (UV) source (350 μW/cm² at wavelength of 365 nm). The images were taken by using the reflection mode of polarizing optical microscope (Olympus BX-43F). The mechanism of UV curing is to enable phase separation between the LC molecules and the NOA65 polymers.

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