PEDOT:PSS-free organic solar cells fabricated on buffer and anode integrated Ta-doped In₂O₃ films

We developed poly(3,4-ethylene dioxylene thiophene):poly(styrene sulfonic acid) (PEDOT:PSS)-free organic solar cells (OSCs) using buffer and anode-integrated Ta-doped In₂O₃ (ITaO) films. By co-sputtering of Ta₂O₅ and In₂O₃ targets, we obtained buffer and anode-integrated ITaO electrodes with a sheet resistance of 17.11 /square, a transmittance of 93.45%, and a work function of 4.9 eV, all of which are comparable to conventional ITO anodes. Since ITaO electrodes have similar electrical and optical transmittance to those of ITO films, the conventional bulk heterojunction OSC with ITaO anode showed a power conversion efficiency (PCE) of 3.348% similar to the OSCs (3.541%) with an ITO anode. In addition, OSCs fabricated on an ITaO electrode successfully operated without an acidic PEDOT:PSS buffer layer and showed a PCE of 2.634%, which was much higher than the comparable OSC with an ITO anode. Therefore, co-sputtered ITaO films simultaneously acting as a buffer and an anode layer can be considered promising transparent electrodes for cost-efficient and reliable OSCs because they can eliminate the use of an acidic PEDOT:PSS buffer layer.