Conjugated Polymers Based on Phenothiazine and Fluorene in Light-Emitting Diodes and Field Effect Transistors

Poly[10-(2‘-ethylhexyl)-phenothiazine-3,7-diyl] (PPTZ), poly[9,9-bis(2‘-ethylhexyl)fluorene-2,7-diyl] (PBEHF), and their random copolymers, poly(BEHF-co-PTZ), were synthesized through Ni(0)-mediated polymerization. Light-emitting devices were fabricated using these polymers in an ITO (indium tin oxide)/PEDOT:PSS/polymer/Ca/Al configuration. Each EL device constructed with a poly(BEHF-co-PTZ) copolymer exhibited significantly enhanced efficiency and brightness compared to devices constructed from the PPTZ and PBEHF homopolymers. The EL device constructed with poly(88BEHF-co-12PTZ) exhibited the highest power efficiency and brightness (4200 cd/m2 and 2.08 cd/A respectively). This enhanced efficiency of the copolymer devices results from their improved hole injection and more efficient charge carrier balance, which arise due to the HOMO levels (∼5.4 eV) of the poly(BEHF-co-PTZ) copolymers, which are lower than that of the PBEHF homopolymer (∼5.8 eV). An organic field effect transistor was also fabricated using PPTZ as a new p-type channel material and characterized. The measured field effect mobility of the transistor was 0.8 × 10-4 cm2/V·s and the on/off ratio of the device was ∼103.