Enhanced electron current in inverted organic light emitting diodes with an n-doped electron transport layer adopting high and low doping levels

Inverted organic light emitting diodes (IOLEDs) have been fabricated using Li2CO3 n-doped bathocuproine (BCP:Li2CO3) to boost electron injection and transport. It is found that the 8:1 BCP:Li2CO3 in mass ratio is more conductive than the 4:1 BCP:Li2CO3, mostly because the higherdoping level Li2CO3 scatters electrons more severely than the lower-doping level one. Nevertheless, the electron injection from cathode to 4:1 BCP:Li2CO3 is confirmed more efficient than that from cathode to 8:1 BCP:Li2CO3, since the higher doping level creates narrower depletion zone at the cathode interface and thereby makes electron tunneling more efficient, compared to the lower doping level. In addition, the transport barrier from 4:1 BCP:Li2CO3 to emissive layer is found smaller than that from 8:1 BCP:Li2CO3 to emissive layer. The IOLED using the cathode/10 nm 4:1 BCP:Li2CO3/10 nm8:1 BCP:Li2CO3/10 nm 4:1 BCP:Li2CO3 structure shows increased performance than its counterparts using the cathode/30 nm 4:1 BCP:Li2CO3 and cathode/30 nm 8:1 BCP:Li2CO3 structures, as a result that the former structure offers an optimized trade-off between reducing the injection loss, conduction loss, and electrical loss due to transport barrier from BCP:Li2CO3 to emissive layer, relative to the latter two. Weprovide a simple and effective method to improve the performance of organic electronic devices based on managing the doping levels of n-doped electron transport layers.