Highly Efficient Inverted Organic Photovoltaics Containing Aliphatic Hyperbranched Polymers as Cathode Modified Layers

In this study, we found that interfacial layers (IFLs) based on wholly aliphatic hyperbranched poly­(amido acid)­s (HBPAs) with interior tertiary amido groups can increase the performance of organic photovoltaics (OPVs) substantially. The performance of constructed devices having the layered configuration glass/indium tin oxide (ITO)/ZnO (with or without IFL)/active layer/MoO3/Ag were enhanced when containing the studied aliphatic HBPAAs, the result of increases in the short circuit current. The presence of the IFL caused the ZnO layers to function more efficiently as electron-selective electrodes. The power conversion efficiencies of the devices incorporating PTB7/PC71BM (from 7.1 to 7.8%) and PffBT4T–2OD/PC71BM (from 7.8 to 8.7%) increased because of physisorption of the aliphatic HBPAAs, thereby changing the ZnO film’s surface energy and altering the active layer’s morphology. We processed these HBPA-based IFLs in air from solution, providing a simple method for the preparation of solution-processable inverted OPVs.