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16 October 2007 Optical characteristics of the OLED with microlens array film attachment
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We investigated the luminance enhancement, spectral shift and image blur of the OLED with the microlens array film (MAF) attachment experimentally and theoretically. Higher density, larger curvature, and smaller diameter of the microlenses extracted more light from the substrate mode. The maximum improvements of the luminance at the normal direction and the total power were 42.5% (80%) and 45% (85%) from our experimental (simulation) results, respectively. The differences between the theoretical and experimental results may come from the non-Lambertian radiation of OLED and the imperfection of the microlens array film. From observing the planar OLED, the peak wavelength is blue-shifted and the full width at the half maximum (FWHM) decreased with respect to increasing viewing angles due to the microcavity effect. When the MAF was attached, the spectral peak had a further blue shift (5 to 10 nm at different viewing angles) compared to that of the planar OLED and it came from the light extraction of the MAF from the substrate mode. We also quantitatively investigated the "blur width" of the OLED with MAF attachment. Higher image blur was observed as accompanied with higher extraction efficiency which showed a tradeoff between the image quality and extraction efficiency. It means that the MAF attachment is more suitable for OLED lighting application, rather than display application. To reduce the image blur and keep the high extraction efficiency at the same time, we re-designed the arrangement of the microlens arrays on the film. In our optimized case, we found that the blur width can be reduced from 79 μm to 9 μm, while the extraction efficiency is kept nearly the same. It shows a possibility to use the microlens array film on real OLED display for improving the extraction efficiency without image quality degradation.
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Hoang-Yan Lin, Jiun-Haw Lee, Mao-Kuo Wei, Kuan-Yu Chen, Sheng-Chih Hsu, Yu-Hsuan Ho, and Chung-Yu Lin "Optical characteristics of the OLED with microlens array film attachment", Proc. SPIE 6655, Organic Light Emitting Materials and Devices XI, 66551H (16 October 2007);

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