Improving the light extraction efficiency of polymeric light emitting diodes using two-dimensional photonic crystals

Enhanced light outcoupling of polymer light-emitting diodes with a solution-processed, -flattening photonic-crystal underlayer

“…In addition to these index-matching approaches, photonic structures like the microlens array have been introduced to the backside of the substrate [6][7][8]. The corrugated structure in the substrate or anode, and the photonic-crystal (PC) structures have also been employed with various fabrication methods involving etching, imprinting, nanosphere-based lithography, or buckling [9][10][11][12][13][14][15][16][17][18].…”

“…Although many variations in the structure have been studied according to their locations, morphologies, and planarization layers, most of the previous studies that dealt with the PC structure fabricated on the substrate adopted an additional planarization process using chemical vapor deposition, chemical mechanical polishing (CMP), or a coating solution-based planarization material to obtain relatively flat substrate surfaces for the following anode fabrication [11,12,17,18]. In the case of the OLEDs without an additional planarization layer, the corrugated form factor typically propagates through each layer of the OLED structure, leading to the enhancement of the light extraction due to the multiple diffractions between the adjacent layers [13][14][15].…”

“…In particular, the thickness variation of the organic layers deposited on the corrugated anode surfaces may cause non-uniformity of the optoelectric characteristics and may induce device instability. The thickness variation especially becomes more problematic for the solution-processed organic layers [11,17,18]. If the flat anode surface without any additional planarization step is obtained through a simple process, it will be a key enabling technology for easily introducing the PC structure into OLEDs, and for fully utilizing its benefit for areal lighting applications.…”

Calculation of the emission power distribution of microstructured OLEDs using the reciprocity theorem

“…Most commonly they have been used to improve the OLED external quantum efficiency, by out-coupling the light trapped in substrate modes, waveguide modes and surface plasmon polaritons [1][2][3][4][5][6][7][8][9][10][11]. To use such devices in displays or lighting applications, such microstructured OLEDs must be designed to provide good angular colour stability.…”

“…Apart from such forward methods, Zhang et al investigated the modes in the microstructured OLEDs in a reverse way by sending an EM plane wave into the OLED at normal incidence and investigating how efficiently it can be coupled into a waveguide [26]. This reported modelling focused on the improvement in light out-coupling efficiencies, however, they did not address the calculation of spatial amplitude of the emission pattern from microstructured OLEDs in the far field, and the need to address such calculations is increasing in the OLED community [1][2][3][4][5][6][7][8][9][10][11][12][13].…”