Atomically-thin LED scales across large areas
Their paper “Scalable Large-Area p−i−n Light-Emitting Diodes Based on WS2 Monolayers Grown via MOCVD” published in the ACS Photonics journal describes a vertical p−i−n device architecture using organic and inorganic injection layers on the anode and the cathode side, respectively, sandwiching WS2 monolayers as the active region.
They report red electroluminescence (at 619.5 ± 0.9nm) from an active area of 6mm2 starting already at a driving voltage of about 2.5V. The novelty is the scalability of their process, using an industrially relevant and reproducible deposition approach in a commercial horizontal multi-wafer AIXTRON MOCVD reactor. Deposited on a 2-inch sapphire wafer, the 0.7nm thick WS2 monolayers could be used to manufacture large area vertically-emitting devices, reaching a luminance of almost 1cd/m2 at 7V.
The paper also reports that operating the LED in pulsed electroluminescent mode reduces heat dissipation, enhancing the device efficiency by a factor of almost 4.
Glass coated with indium tin oxide (ITO) is used as the anode material, with poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS) as a hole injection layer, and poly[N,N′-bis(butylphenyl)-N,N-bis(phenyl)benzidine] (poly-TPD) as organic hole transport layer. On the cathode side, a ZnO quantum dot (ZnO-QD) layer serves as the electron injection layer on an aluminium cathode.
Universität Duisburg-Essen – www.uni-due.de
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