Conjugated zwitterionic polyelectrolyte-based interface modification materials for high performance polymer optoelectronic devices

A series of new water/alcohol-soluble conjugated polymers (WSCPs) poly[(9,9-bis((N-(4-sulfonate-1-butyl)-N,N-dimethylammonium)propyl)-2,7-fluorene)-alt-N-phenyl-4,4'-diphenylamine)] (PFNSO-TPA), poly[(9,9-bis((N-(4-sulfonate-1-butyl)-N,N-dimethylammonium)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFNSO) and poly[(9,9-bis((N-(4-sulfonate-1-butyl)-N, N-dimethylammonium) propyl)-2,7-fluorene)-alt-4,7-(2,1,3-benzothiadiazole)] (PFNSO-BT), comprising identical sulfobetaine zwitterionic groups on their side chains but different conjugated main chain structures, were designed and developed as interface modification materials to improve electron collection in bulk-heterojunction polymer solar cells (PSCs), and to improve electron injection/transporting in polymer light-emitting diodes (PLEDs). The resulting WSCPs possess integrated advantages of excellent alcohol processability, interface modification functions and mobile ion free nature. The relationships between the WSCPs main chain structures and properties (including optical/electrical properties and interface modification functions in resulting devices) were investigated systematically. In PSCs, it was found that the WSCPs interface modification properties led to varying differences, but all of them can boost the photovoltaic performances of PSCs; encouragingly, a high power conversion efficiency (PCE) of 8.74% could be achieved. In PLEDs, the interface modification functions of the WSCPs strongly depend upon their conjugated main chain structures. The WSCPs should possess suitable energy levels to match well with the light-emitting layer (EML), even though the electron injection from metal cathode was efficient. Our results show promising potentials of WSCPs as interface modification layers in organic/polymer optoelectronic devices, and provide new insights for the development of new interface modification materials in the future.