Organic semiconductor heterojunctions as charge generation layers and their application in tandem organic light-emitting diodes for high power efficiency

Abstract

Organic light-emitting diodes (OLEDs) can convert injected charge into photons. The upper conversion limit of single-unit OLEDs is at most one photon per injected electron. Alternatively, tandem OLEDs that vertically stack several single-unit OLEDs via charge generation layers (CGLs) can convert one injected electron into multiple photons, thus achieving greater brightness and current efficiency with a lower current. However, since the driving voltage consumed by conventional tandem devices scales linearly with the number of electroluminescent units, the resulting power consumption would be the same for both the single-unit and tandem OLEDs to obtain the same luminescence; this means that the power efficiency cannot be greatly increased for such tandem devices. Recently we found that using buffer-modified intrinsic organic semiconductor heterojunctions (OHJs) as the CGLs significantly enhanced the power efficiency of the fabricated tandem OLEDs, which was previously suggested to be difficult for tandem devices. In this feature article, we review the recent advances of tandem OLEDs based on OHJs as the CGLs, including the design concept and basic requirements of the energy levels and mobility of involved organic semiconductors. Our results show that the use of OHJs as CGLs is a universal concept for the fabrication of tandem OLEDs with high power efficiency. We believe that the concept of OHJs opens new perspectives for the rational design of CGLs to realize tandem devices with unprecedented improvement in power efficiency. In particular, it has great potential for use in the fabrication of tandem white OLEDs (WOLEDs) for solid-state-lighting. Yonghua Chen Dr Yonghua Chen received his BE degree in chemistry from Inner Mongolia University in 2006 and then joined Dr Dongge Ma's group at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (CAS), where he obtained his Ph.D. in polymer chemistry and physics in 2011. Currently, he is doing his postdoctoral research at Wake Forest University. His research interests include tandem organic light-emitting diodes and field-induced polymer electroluminescent devices for flat panel displays and solidstate lighting.

Relation between Interfacial Band‐Bending and Electronic Properties in Organic Semiconductor Pentacene

“…[7] Moreover, heterojunction films with high conductivity were also used as connecting layer in tandem devices. [8,9] Furthermore, the organic/electrode contacts were found to be a fundamental element in semiconductor devices. [10] Their interfacial electronic structures can influence or determine the device performance and function, since charge www.advelectronicmat.de film was obtained to be 2.20 eV, so, the Fermi level of ITO is located at the position of a bitter lower than the middle of band gap of pentacene before contact.…”

Control over the photophysical properties of nanoparticles of regioregular poly(3-octylthiophene) using various poor solvents

“…The face-on orientation, promoting the charge transport along the film surface, is desirable for PSCs [13]. For OLED devices, the polymer film should contain minimal fraction of aggregates to achieve high electroluminescent intensity [5].…”

“…Regioregular poly(3-alkylthiophene) (rr-P3AT) is an important semicrystalline conjugated polymer which can be utilized in organic electronic technologies such as polymer solar cells (PSCs) [1][2][3], organic light-emitting diodes (OLEDs) [4,5], and organic field-effect transistors (OFETs) [6][7][8]. Their environmental stability and large extent of p-orbital overlapping in their crystalline structure, resulting in relatively high charge carrier mobility, make them suitable for these advanced technologies [9][10][11].…”

Interconnectors in Tandem Organic Light Emitting Diodes and Their Influence on Device Performance

“…via the interconnectors, with the entire device driven by a single power source [15]- [18]. When certain voltage is applied on the electrodes, each EL lights up individually under the same current that flow through the whole device (a simple schematic diagram is given in Fig.…”