Abstract
We investigated a low-temperature mask-free process for preparing random nanoscale rods (RNRs) as a scattering layer. The process involves spin coating and dry etching, which are already widely applied in industry. Our film exhibited 17–33% optical haze at 520 nm wavelength and 95% total transmittance in the visible range. Therefore, this film can be used as a scattering layer for improving viewing angle characteristics and decreasing substrate mode loss in organic light-emitting diodes (OLEDs). Specifically, we focussed on varying the height and density of the RNRs to control the optical characteristics. As a result, the OLEDs with RNRs revealed a variation in colour coordinates of Δ(x, y) = (0.007, 0.014) for a change in the viewing angle, which was superior to those without the RNRs that displayed a variation of Δ(x, y) = (0.020, 0.034) in CIE 1931. Moreover, the OLEDs with RNRs exhibited 31% enhanced external quantum efficiency compared to those of the OLEDs with the bare substrate. The flexibility of the polymer used for the RNRs and the plasma treatment suggests that the RNRs can be applied to flexible OLED displays and lighting systems.
Highlights
Organic light-emitting diodes (OLEDs) are being widely applied in displays for mobiles and televisions owing to their self-emitting characteristics, excellent colour gamut, high-speed operation, and applicability in flexible or stretchable devices[1]
To investigate the optical effect of random nanoscale rods (RNRs) on glass, the electrical field distribution was simulated by the finite-difference time domain (FDTD) method
The simulated structure consisted of an aluminium cathode, N,N’-bis(naphthalen-1-yl)-N,N’-bis(phenyl)-benzidine (NPB; refractive index n = 1.81), tris(8-hydroxy-quinolinato)aluminium (Alq[3]; n = 1.72), indium tin oxide (ITO) (n = 1.9), glass (n = 1.52), SU-8 polymer, and RNRs (n = 1.59)
Summary
To investigate the optical effect of RNRs on glass, the electrical field distribution was simulated by the finite-difference time domain (FDTD) method. Considering the total transmittance and haze, the treatment condition of RNRs 2 was expected to produce the optimal height and density of rods for enhanced light extraction of OLEDs. The electrical characteristics of the device with and without the RNRs were almost identical since they were placed, where they do not affect the devices (Fig. 4a). As a result of the maximum difference in the colour coordinates in CIE 1931 for viewing angles varying from 0° to 70°, the reference device exhibited a variation of Δ(x, y) = (0.020, 0.034), whereas the RNRs 2 device revealed a variation of Δ(x, y) = (0.007, 0.014) (Supplementary Information Fig. S5) This result proved that the RNRs played appropriate roles as scattering layers. We believe that this study will open a new and practical approach to improving the performance of high-resolution displays and flexible lightings
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