Two-unit tandem organic light emitting diodes (OLEDs) employing two kinds of interconnecting structures, i.e.

In this study, inverted organic light emitting diodes (OLEDs) have been fabricated using the doped p–n heterojunction composed of poly(3,4-ethylenedioxythiophene) :poly(styrenesulfonate) (PEDOT:PSS) and lithium carbonate doped bathocuproine (Li2CO3:BCP) to provide the electron current. The field-induced charge-carrier separation at the doped organic/organic heterointerface was adopted to illuminate the process of generating electron current. Nevertheless, the performance of the inverted OLEDs remained nearly invariable when the PEDOT:PSS thickness ranged from 15 to 38 nm. This was understood mostly based on the temporary reduction of the PEDOT+ to the PEDOT0 due to the localized electron in the PSS− being repelled back to the highest occupied molecular orbital of the PEDOT+ by electrons accumulated at the cathode/PEDOT:PSS interface. The current research presents an insightful understanding of the electrical properties of an organic doped p–n junction that is reversely biased.