In a new review article (Recent advances in light outcoupling from white organic light-emitting diodes) in the Journal of Photonics for Energy, my colleague Malte C. Gather (University of St. Andrews) and I summarize the recent efforts on the development of concepts for light outcoupling in white organic light-emitting diodes (OLEDs). Especially with respect to the complementary inorganic LED technology, it is extremely important to unlock higher external quantum efficiencies in OLEDs to stay competitive. Here, improving the outcoupling efficiency by far offers the largest margin (standard structures are at 20-30% of the internal efficiency maximum). The current status reveals that a universal solution with satisfying enhancement still waits to be found.
Published in the April 2014 issue of Nature Photonics, the group of Chihaya Adachi report on highly efficient blue OLEDs based on the novel thermally activated delayed fluorescence (TADF) concept (Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence). This is yet another important and equally impressive milestone in the OLED field, which puts these novel emitters on par with phosphorescence emitting molecules (at least with respect to their efficiency).
Along with the paper mentioned above, I express my thoughts about this development in a Nature Photonics News & Views feature. Read it here: Phosphorescence meets its match. I expect to see white TADF OLEDs coming in 2014.
Singlet exciton fission – a process found in special organic semiconductors – splits a high energy singlet state, which is created upon photon absorption, into two, low-energy triplet states of equal energy. Incorporating such organic materials in a photovoltaic cell paves the way to more carriers produced per incident photon flux.
Based on the singlet fission archetype material pentacene, in an exciton confining architecture around a heterojunction with the fullerence acceptor C60, we (Congreve et al., Science 340, 334 (2013)) have demonstrated an external quantum efficiency of an organic solar cell exceeding 100%, breaking the barrier of one electron per photon in the visible spectrum.