Multi-channel interface dipole of hyperbranched polymers with quasi-immovable hydrion to modification of cathode interface for high-efficiency polymer solar cells

The single-junction polymer solar cells (PSCs) with high power conversion efficiency (PCE) are demonstrated by first incorporating two hyperbranched polymers (carboxylic acid functionalized hyperbranched poly(ether ketone) (CHBPEK) and sulfonic acid functionalized hyperbranched poly(ether sulfone) (SHBPES)) with carboxylic and sulfonic acid groups to modify the cathode interface. The effect of cathode modification by CHBPEK or SHBPES for conventional PSCs based on different active-layer materials is systematically investigated. Compared with traditional LiF/Al, Ca/Al, and PFN/Al devices, significant improvement in short circuit current and fill factors are achieved by employing CHBPEK or SHBPES. In particular, the device with SHBPES as cathode interlayer can be achieved with a highest PCE of 9.12%, which are among the high performance reported for single-junction PSCs modified with hyperbranched interlayers. Importantly, the influence of the hyperbranched polymer interlayer modification on the cathode interface is also discussed and found to be the formation of the stable multi-channel interface dipole based on quasi-immovable counterions in these polymers. The results supply a feasible means to obtain the improved J(SC) and FF for high efficiency PSCs. Copyright (c) 2016 John Wiley & Sons, Ltd.