Active refractive index control using a stably evaporable perfluororesin for high-outcoupling-efficiency organic light-emitting diodes

Abstract

The internal quantum efficiency of organic light-emitting diodes (OLEDs) has reached nearly 100%, and thus further improvement in the external quantum efficiency can be achieved only through outcoupling enhancement. However,...

Improved Light Extraction in Organic Light‐Emitting Diodes via Semiconductor Dilution

“…Ohmic contacts are facilitated by using MoO 3 (5 nm)/ 4,4′-Bis(N-carbazolyl)−1,1′biphenyl (CBP, 5 nm) buffer layers [31] that also serve to prevent changes in interface energy level alignment that can occur when fluorinated dilution materials directly contact the electrodes. [22,23] The J-V data are fit using the Mott-Gurney relation using a field-and temperature-dependent mobility given by the Murgatroid-Gill model [32,33] as described in Ref. [23] The results, which are summarized in Figure 2b, show that the zero-field mobility changes little with increasing F-POSS concentration up to 40 vol.%, but declines rapidly beyond that, with a tenfold de-crease at 60 vol.%.…”

“…Though F-POSS is not the first low index dilution material to be used in OLEDs, [21][22][23]28] it is significant because it is a small molecule that sublimes cleanly, can be purified by gradient sublimation, and does not phase segregate in blends. In short, F-POSS can be purified, processed, and used just like any other small molecule in vacuum deposited OLEDs, which is critical for adoption in industry.…”

“…As in Refs. [22,23], the electron trapping behavior of F-POSS is presumably associated with fluorination which, unfortunately, is also the key to its low refractive index. Non-fluorinated POSS derivatives exist with slightly higher refractive indices ≈1.5 that may offer a path for ETL dilution.…”

“…[14] This strategy has been pursued using organic semiconductors that have naturally low refractive index (n ≈ 1.6 compared with n > 1.7 for most OLED materials across the visible spectrum), [15][16][17][18][19] nanoporous organic semiconductors, [15,16] and low index electrical contacts made of materials such as poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS; n ≈ 1.5). [20] Alternatively, the refractive index of traditional organic semiconductors can be de-creased by co-evaporating them with low index materials such as LiF, [21] perfluorinated oligomers, [22] and polymers. [23] Although the addition of such insulators would normally be expected to degrade electrical transport, the notion of semiconductor dilution [24,25] and critical percolation threshold [25,26] for small molecule-insulator blends motivates the possibility of lowering index without sacrificing transport.…”

Design of a Structure for Optimized Optical Performance of a Full Colored Organic Light-Emitting Diode on a Parameter Space Map

“…Several researchers have used a numerical approach to perform the spectrum at visible wavelengths and calculate the full width at half-maximum (FWHM) and central wavelength in the RGB structure in each situation of changing layer thickness or optical constant index [ 15 , 16 , 17 , 18 , 19 ]. Therefore, the thickness can be optimized based on the required optical characteristics.…”