Fast Organic Vapor Phase Deposition of Thin Films in Light-Emitting Diodes

Abstract

Fast deposition of thin films is essential for achieving low-cost, high-throughput phosphorescent organic light-emitting diode (PHOLED) production. In this work, we demonstrate rapid and uniform growth of semiconductor thin films by organic vapor phase deposition (OVPD). A green PHOLED comprising an emission layer (EML) grown at 50 Å/s with bis­[2-(2-pyridinyl-N)­phenyl-C]­(acetyl­acetonato)­iridium­(III) (Ir­(ppy)2(acac)) doped into 4,4′-bis­(N-carbazolyl)-1,1′-biphenyl (CBP) exhibits a maximum external quantum efficiency of 20 ± 1%. The morphology, charge transport properties, and radiative efficiency under optical and electrical excitation of the PHOLED EML are investigated as functions of the deposition rate via both experimental and theoretical approaches. The EML shows no evidence for gas phase nucleation of the organic molecules at deposition rates as high as 50 Å/s. However, the roll-off in quantum efficiency at high current progressively increases with deposition rate due to enhanced triplet-polaron annihilation. The roll-off results from accumulation of stress within the PHOLED EML that generates a high density of defect states. The defects, in turn, act as recombination sites for triplets and hole polarons, leading to enhanced triplet-polaron annihilation at high current. We introduce a void nucleation model to describe the film morphology evolution that is observed using electron microscopy.

Printable Organic Electronic Materials for Precisely Positioned Cell Attachment

“…Because of its relatively low vaporization enthalpy, 39 CBP is readily printable using OVJP, as shown by the printed pattern decorated with cells in Figure 4a. Sample rotation during deposition produces the apparent bowtie pattern whose A notable feature of this pattern is that the neck of the bowtie is approximately 10 μm wide.…”

Cost Estimates of Roll-to-Roll Production of Organic Light Emitting Devices for Lighting

“…Estimates of the current cost of illumination for WOLED lighting vary from $50 to $300/klm based on different assumptions of commercial product margin and panel efficacies. , The adoption of WOLED lighting ultimately hinges on whether it is cost competitive with other types of solid state lighting appliances and whether volume production is feasible. High speed fabrication of organic semiconductors on flexible substrates that are compatible or integrated with roll-to-roll (R2R) processing has been demonstrated, − yet a detailed cost analysis of manufacturing large area WOLED panels at high volume using R2R methods, to our knowledge, remains to be explored. , Furthermore, the cost of drivers adapted to WOLED lighting and miscellaneous costs such as taxes, administrative, and marketing need to be considered to estimate the true production costs of this lighting technology.…”

Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition

“…Organic thin films are an effective material for device applications, such as organic light emitting diodes (OLEDs) and organic photovoltaics [ 1 , 2 , 3 , 4 , 5 , 6 ]. Developing methods for the deposition of organic thin film has been an important research topic in the material sciences fields for a long time [ 4 , 5 , 6 , 7 , 8 ]. One of many urgent issues regarding organic thin film is to achieve high quality—in terms of surface smoothness—that is largely hindered by the uncontrolled nucleation of target molecules or the formation of irregular aggregates [ 7 , 9 , 10 , 11 , 12 ].…”

“…Developing methods for the deposition of organic thin film has been an important research topic in the material sciences fields for a long time [ 4 , 5 , 6 , 7 , 8 ]. One of many urgent issues regarding organic thin film is to achieve high quality—in terms of surface smoothness—that is largely hindered by the uncontrolled nucleation of target molecules or the formation of irregular aggregates [ 7 , 9 , 10 , 11 , 12 ]. Therefore, inhibiting abrupt nucleation and suppressing aggregates during film formation are two reasonable pathways for the formation of highly smooth films.…”

“…The most conventional and standard method for the preparation of organic film is to deposit organic vapors under a high-vacuum environment (referred to as the ‘high-vacuum method’) [ 7 , 10 , 16 , 17 , 18 , 19 ]. A low-vacuum method, represented by physical vapor deposition (PVD) is an alternative [ 20 , 21 , 22 , 23 ].…”