3.3.4.1. Light-emitting diodes (LEDs)
rod–coil copolymers containing both electron and hole transporting functionalities can exhibit balanced charge injection and transport through the LED device under an applied voltage bias. For example, a bipolar rod–coil block copolymer (PPV-b-OX) with a PPV rod-shaped block as the hole transporting and emitting material and poly(vinyloxadizaole) coil-shaped electron transporting block, displayed phase separated lamelle regimes oriented both parallel to and perpendicular from the electrodes [119]. As shown in Fig. 30, The LEDs using block copolymers exhibited higher efficiencies and brightness than those using either pure PPV or a blend of the two analogous homopolymers. The improved performance with microphase separation mainly resulted from the maximum effective interfacial area between the electron and hole transporting domains, which facilitated exciton formation. Well-defined polyfluorene-based rod–coil block copolymers containing flexible hole transport carbazole segments were shown to improve the hole injection, while enhancing the blue emission features [63]. The controllable nanoscale morphology of conjugated rod–coil block copolymers affected the charge transport ability and tuned the efficiency of LEDs devices.