Abstract
Organic light-emitting diodes (OLEDs) have been established as versatile light sources that allow for easy integration in large-area surfaces and flexible substrates. In addition, the low fabrication cost of OLEDs renders them particularly attractive as general lighting sources. Current methods for the fabrication of white-light OLEDs rely on the combination of multiple organic emitters and/or the incorporation of multiple cavity modes in a thick active medium. These architectures introduce formidable challenges in both device design and performance improvements, namely, the decrease of efficiency with increasing brightness (efficiency roll-off) and short operational lifetime. Here we demonstrate, for the first time, white-light generation in an OLED consisting of a sub-100 nm thick blue single-emissive layer coupled to the photonic Bragg modes of a dielectric distributed Bragg reflector (DBR). We show that the Bragg modes, although primarily located inside the DBR stack, can significantly overlap with the emissive layer, thus efficiently enhancing emission and outcoupling of photons at selected wavelengths across the entire visible light spectrum. Moreover, we show that color temperature can be tuned by the DBR parameters, offering great versatility in the optimization of white-light emission spectra.
Highlights
Organic light-emitting diodes (OLEDs) have been established as versatile light sources that allow for easy integration in large-area surfaces and flexible substrates
OLEDs have been utilized in a plethora of optoelectronic applications,[2,3] and the effort for improving their efficiency constitutes one of the major trends in modern optoelectronics research.[4−6] Owing to their low fabrication cost, exceptional color rendering, and ease of deposition to large areas and flexible substrates, OLEDs have attracted a lot of attention as general illumination devices in which broadband and high-intensity white light is a key requirement.[7,8]
Achieving the desired color balance requires precise control over the thickness and composition of each layer which makes the fabrication of such white organic light-emitting diodes (WOLEDs) complicated, rendering them incompatible as inexpensive solid-state lighting sources.[11,12] (2) Single-emissive layer structures in which white light is achieved via nearmolecule energy transfer (Förster or Dexter) between a matrix material and multiple dopant emitters
Summary
Color ratio of red, green, and blue is primarily defined by the optical modes, the white-light spectrum is expected to be uninfluenced by variations in doping, carrier competition, and other molecular emission instabilities. Letter spectral region of the WOLED (Figure S5), but it could be attributed to the efficient outcoupling of emission from bimolecular excited states formed in the interface of TDAF and BPhen.[30,31] Note that the Bragg converter concept can be potentially utilized in other contexts, such as for harvesting energy from long-lived triplet states either through strong coupling[32−34] (Figure S4) or by typical photon upconversion or phosphorescence mechanisms.[35,36] In addition to the improved external quantum efficiency, the encapsulation of the OLED in the dielectric Bragg converter results in a more than 30-fold increase of on-shelf lifetime compared to nonencapsulated.
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