Investigating underlying mechanism in spectral narrowing phenomenon induced by microcavity in organic light emitting diodes

Abstract

This paper reports our experimental studies on the underlying mechanism responsible for electroluminescence spectral narrowing phenomenon in the cavity-based organic light-emitting diodes. It is found that the microcavity generates an emerging phenomenon: a magneto-photoluminescence signal in Poly(9,9-dioctylfluorene-alt-benzothiadiazole) polymer under photoexcitation, which is completely absent when microcavity is not used. This provides an evidence that microcavity leads to the formation of spatially extended states, functioning as the intermediate states prior to the formation of Frenkel excitons in organic materials. This is confirmed by the magneto-electroluminescence solely observed from the cavity-based light-emitting diodes under electrical injection. Furthermore, the narrowed electroluminescence output shows a linear polarization, concurrently occurred with magneto-electroluminescence. This indicates that the spatially extended sates become aligned towards forming coherent light-emitting excitons within the microcavity through optical resonance. Clearly, the spatially extended states present the necessary condition to realize electroluminescence spectral narrowing phenomenon towards lasing actions in cavity-based organic light-emitting diodes.

Two‐Photon Up‐Conversion Photoluminescence Realized through Spatially Extended Gap States in Quasi‐2D Perovskite Films

“…After scratching, the PL from small-n-value nanoplates becomes dominant. [32,33,35] Therefore, magneto-PL can be used as an in situ method to elucidate the characteristics of light-emitting states involved in gap states-induced twophoton up-conversion PL in quasi-2D perovskites. Clearly, by using mechanical scratching method, the similar PL spectra provide a solid evidence to confirm that the different-n-value nanoplates are uniformly arranged between the bottom and top surfaces in our quasi-2D perovskite films prepared with antisolvent processing.…”

Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes

“…Distributed Bragg reflectors (DBRs) can significantly enhance the cavity resonance to achieve directional emission and even lasing (Figure S1a, Supporting Information). [ 16–20 ] The layered structure of DBRs is compatible with thin‐film LED fabrication, but the emission direction is sensitive to the cavity length and its emission spectrum is highly angle dependent (Figure S2, Supporting Information). Alternatively, thin‐film LED pixels can be made into line or point sources with microlens arrays to collimate the emitted light (Figure S1b, Supporting Information).…”

Microcavity‐Enhanced Blue Organic Light‐Emitting Diode for High‐Quality Monochromatic Light Source with Nonquarterwave Structural Design

“…The key reasons are the following: 1) the wide spectrum of organic materials makes the angular dispersion of MOLEDs very serious, which would affect the beam quality; ) the lack of a reasonable resonator structure to control the spontaneous emission characteristics of OLEDs effectively. At present, metal cavities or metal‐dielectric cavities are mostcommonly used in MOLEDs, and all‐dielectric MOLEDs have also been reported, but the overall performance is poor owing to the extra optical loss in the resonator is difficult to control. It is worth noting that constructing a reasonable microcavity is not easy to achieve by adopting the existing structural parameters.…”