Transition metal dichalcogenides (TMDCs) represent a novel and sustainable material basis for ultrathin optoelectronic devices. Although various approaches toward light-emitting devices, e.g., based on exfoliated or chemical vapor deposited (CVD) TMDC monolayers, have been reported, they all suffer from limited scalability and reproducibility required for industrial fabrication. Here, we demonstrate a light-emitting device in a scalable approach by embedding metal−organic (MO-)CVD WS2 monolayers into a vertical p–i–n device architecture using organic and inorganic injection layers. Red electroluminescence is emitted from an active area of 6 mm2 starting already at a driving voltage of about 2.5 V.
Transition metal dichalcogenide (TMDC) monolayers with their direct band gap in the visible to near-infrared spectral range have emerged over the past years as highly promising semiconducting materials for optoelectronic applications. Progress in scalable fabrication methods for TMDCs like metal-organic chemical vapor deposition (MOCVD) and the ambition to exploit specific material properties, such as mechanical flexibility or high transparency, highlight the importance of suitable device concepts and processing techniques. In this work, we make use of the high transparency of TMDC monolayers to fabricate transparent light-emitting devices (LEDs). MOCVD-grown WS2 is embedded as the active material in a scalable vertical device architecture and combined with a silver nanowire (AgNW) network as a transparent top electrode. The AgNW network was deposited onto the device by a spin-coating process, providing contacts with a sheet resistance below 10 Ω sq-1 and a transmittance of nearly 80 %. As an electron transport layer (ETL) we employed a continuous 40 nm thick zinc oxide (ZnO) layer, which was grown by atmospheric pressure spatial atomic layer deposition (AP-SALD), a precise tool for scalable deposition of oxides with defined thickness. With this, LEDs with an average transmittance over 60 % in the visible spectral range, emissive areas of several mm2 and a turn-on voltage of around 3 V are obtained.
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