Efficiency exceeding 10% for inverted polymer solar cells with a ZnO/ionic liquid combined cathode interfacial layer

The interlayer inserted between the active layer and ITO has been demonstrated to be crucial for the performance of inverted polymer solar cells (i-PSCs). In this work, we find that ionic liquids (ILs) can significantly enhance the efficiency of i-PSCs. With the ZnO/IL interfacial layer, PTB7-Th : PC71BM i-PSCs can exhibit a champion power conversion efficiency (PCE) of 10.15%, which is among the highest PCEs reported thus far for single-junction bulk heterojunction solar cells through the solution process. The IL layer and ZnO/IL combination layer with low work function, good optical transmittance, improved electron extraction and reduced resistance at the cathode interface have been demonstrated to be excellent and general interfacial layers for i-PSCs.