Multilayer polymer light-emitting diode and solar cell by blade coating

Multilayer polymer light-emitting diode (PLED) and solar cell are fabricated by blade coating. Multilayer of semiconducting polymers can be easily deposited by blade coating without layer mixing, as confirmed by the total thickness and cross section view in scanning electron microscope. The film thickness variation is only 3 % in 10 cm scale and the film roughness is about 0.3 nm in the micron scale. In addition blade coating has the advantages of low material waste and easy scaling up to the meter scale. For blue fluorescent emission, the current efficiency of 5 cd/A is achieved for a three layer structure with hole transport, emissive, and electron transport layers. Only soluble small molecules are used for all the three layers. For green emission phosphorescent emission of 45 cd/A is achieved for a combination of polymer and small molecules. The efficiency for deep red is 4 cd/A based on polymers and small molecules. In all devices efficient electron injection is realized by a blade coated electron transport layer combined with the relatively stable LiF/Al cathode, in contrary the unstable CsF/Al cathode conventionally used for high efficiency PLED. Patterned multi-color PLED is achieved by an epoxy mask during blade coating.