High-efficiency blue multilayer polymer light-emitting diode fabricated by a general liquid buffer method

A bright, highly efficient blue polymer light-emitting diode is fabricated by spin-coating with multilayer structure. By introducing a liquid buffer layer, the dissolution problem is overcome successfully. This general method can be applied to fabricate arbitrary polymer multilayer structure, in particular the addition of the carrier blocking layers to balance the electron and hole currents and improve the device efficiency. By adding an electron-blocking layer, the external quantum efficiency for blue emission can be increased to 5.5% (9.1 cd/A) which is even higher than the theoretical limit of 5%. The luminance reaches 26,530 cd/m2and the Commission Internationale de L’Eclairage (CIE) coordinates is (0.15, 0.23). Further more the lifetime is increased by three times relative to the single layer device.