Transition metal dichalcogenides for organic light emitting diodes and phototovoltaic cells
Recently, MoS2 and WS2 have attracted increasing attention because of their great potential as semiconductors of electronic devices such as field-effect transistors, organic photovoltaics, memory, logic, and energy storage devices. The oxidation state of the Mo and W atoms is +4 and that of the S atom is -2, meaning that MoS2 and WS2 are terminated with S atoms on the upper and lower side. The lone-pair electrons on the surfaces and the absence of dangling bonds in MoS2 and WS2 layers enhance the stability against reactions with other chemical species. Transition metal dichalcogenides (TMDs) were prepared by chemical vapor deposition method or sonication process. This seminar will show that TMDs could be used as charge transport layers in organic light emitting diodes (OLEDs) and photovoltaic cells (PVs).
First, TMDs were used in order to enhance the stability in air comparing to poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). TMD layers with a polycrystalline structure were synthesized by a chemical deposition method using uniformly spin-coated (NH4)MoS4 and (NH4)WS4 precursor solutions. OLEDs and OPV cells based on TMD showed two to six times longer stability in air compared with PEDOT:PSS based devices. Second, TMD layers were applied as the hole transport layer as well as the template for highly polarized OLEDs. The MoS2 nanosheets were patterned by rubbing/ion-beam treatment. The use of patterned MoS2 nanosheets not only tuned the polarization of the OLEDs but also dramatically improved the device performance as compared with that of devices using untreated MoS2.