Improvement of efficiency and stability of polymer light-emitting devices by modifying indium tin oxide anode surface with ultrathin tetrahedral amorphous carbon film

Poly(p-phenylene vinylene)-based polymer light-emitting devices using different thicknesses of tetrahedral amorphous carbon ultrathin films between indium tin oxide and polyethylenedioxythiophene hole transporting layer have been fabricated. The device with a 0.5 nm tetrahedral amorphous carbon (ta-C) layer has the highest luminance and current efficiency compared to that of other devices. The current efficiency of a standard device without a ta-C layer is 1.1 cd/A at 5 V, however, the current efficiency of a device with a ta-C layer thickness of 0.5 nm is 2.7 cd/A; the current efficiency is improved about 2.5 times compared to the standard device. The improvement of the efficiency is due to blocking the hole injection from anode and balancing the hole and electron current. The lifetime of a device with a ta-C layer is significantly much longer than the standard device, and the device with a 0.5 nm ta-C layer has the longest lifetime.