ITO Electrode with a Tunable Work Function for Organic Photovoltaic Devices

Developing methods to tune the work function (WF) of indium tin oxide (ITO) is highly important for the development of high-performance organic photovoltaic (OPV) devices. Here, we achieve tuning of the WF of ITO by over 1 eV by performing O2 plasma treatment on the ITO modified by an organic interlayer material named polyethylenimine ethoxylated (PEIE). More specifically, we show that the WF of the PEIE-modified ITO is 4.02 eV, and it continuously increases with increasing plasma treatment duration, and we demonstrate that the tunability of the WF of ITO is maintained in the OPV devices based on the plasma-treated PEIE/ITO electrode. This allows us to realize OPV devices with the desired energy-level alignments at the ITO/active layer interface, high built-in electric field (Ebi), and good device performance, using the PEIE/ITO electrode acting as either the cathode or the anode. Finally, we show that the WFs of plasma-treated PEIE/ITO electrodes are highly stable. These results indicate that the plasma-treated PEIE/ITO with tunable WF is highly promising in the field of OPV.