Transition metal dichalcogenides (TMDCs), which are MoS2 and WS2 in this experiment, were used as hole transport layers (HTL) in organic light-emitting diodes (OLEDs) and hole extraction layer (HEL) in organic photovoltaic (OPVs) cells in order to enhance the stability in air condition. TMDCs were synthesized by chemical vapor deposition method with spin-coated (NH4)2MS4 (M = Mo, W) precursor and small amounts of sulfur power. To modulate the low work function of synthesized TMDCs, the UV/ozone (UV/O3) surface treatment was performed. The properties of synthesize TMDCs were evaluated by transmission and field emission scanning electron microscopy, Raman spectroscopy, and synchrotron radiation photoemission spectroscopy. Green OLED and OPV devices were fabricated with raw and UV/O3 treated TMDC on indium-tin oxide electrode. The turn-on voltages of OLED with UV/O3 treated TMDCs were 4.4 V (MoS2) and 4.1 V (WS2), which decreased from 5.2 V (pristine MoS2) and 5.1 V (pristine WS2). The best luminance efficiency of OLED based on UV/O3 treated TMDCs was 11 cd/A, which was similar to the efficiency of OLED based on poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). The power conversion efficiencies of OPVs using UV/O3 treated TMDCs as HEL were equivalent to 95 % efficiency of PEDOT:PSS based ones. However, it should be noted that TMDC-HTL OLEDs and TMDC-HEL OPVs show better properties in view point of air stability. Even after the OLED devices were kept at air condition for 38 hours, the green OLED devices are still lighting, but the PEDOT:PSS one is not working. Furthermore, it is shown that the air stability of OPVs using TMDCs as HEL is longer about 2~3 times comparing with OPV based on PEDOT:PSS. These results suggest that the UV/O3 surface treated TMDCs could be a promising candidate in application to optoelectronic devices as a HTLs and HELs.

Extension of air stability in organic light-emitting diodes using MoS2 and WS2 synthesized by chemical vapor deposition

249th National Meeting (2015)

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