Water/Alcohol Soluble Conjugated Polymer Interlayer Materials and Their Application in Solution Processed Multilayer Organic Optoelectronic Devices

Comparing with traditional inorganic semiconductor devices, the organic optoelectronic devices based on organic semiconductors, especially polymer semiconductors, exhibit several distinct advantages, such as low cost, light weight, solution processibility, flexibility and compatibility with roll-to-roll printing etc., and have drawn much attention from both academic and industrial fields. To fulfil solution processed high performance organic optoelectronic devices, one of the major challenges is to avoid interface erosion during solution processing as well as to improve the electron injection/extraction between printable high work function metals and active layers. Water/alcohol soluble conjugated polymers (WSCPs), which are composed of conjugated backbones and highly polar side chains, can be processed from water, alcohol and other polar solvents. The unique solubility of WSCPs provide them with good opportunities to fabricate multilayer organic optoelectronic devices without interface mixing by solution processing, and it is found that WSCPs exhibit promising interface modification capability for high work function metal and/or metal oxide electrodes, which can greatly enhance the performance of organic optoelectronic devices. In this feature article, we gave an overview of our design strategies and achievements on WSCPs, including neutral amine based WSCPs and their quaternized derivatives, WSCPs without mobile counterions, cross-linkable WSCPs, WSCPs towards large area module device, and their applications as interface modification layers in solution processed highly efficient multilayer organic optoelectronic devices. A brief induction and discussion on working mechanisms of WSCPs serving as cathode modification layers in polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs) were also provided. The excellent cathode modification capability of WSCPs can be ascribed to: (a) WSCPs decrease the work function of cathode to increase the build in potential of devices as well as increase the open voltage (V-oc); (b) WSCPs dope contacted PCBM at the interface to increase the conductivity and improve short-circuit current density (J(sc)); (c) WSCPs exhibit excellent electron-extraction and hole-blocking properties at the interface and increase the fill factor (FF).