Enhancing phase separation with conformation-locked nonfullerene acceptor for over 14.4% efficiency solar cells
To fine-tune the morphology and miscibility in active layer of organic solar cells (OSCs), the molecular backbone design and sidechain control are complex and challenging for acceptor-donor-acceptor type nonfullerene acceptors. In this work, both fluorination on accepting ends and sidechain modification on central donating core were optimized for the design of fused-ring electron acceptors (FREAs). Sidechain-locked conformation finely modulates the molecular energy levels and improves the miscibility with weakened structure order. Fluorination effectively enhances the crystallinity to afford an enlarged phase separation and higher domain purity. Benefiting from their synergistic effects, the as-designed ITC6-4F when blended with PM7 polymer donor enables an impressive power conversion efficiency of 14.47% with a high VOC of 0.90 V and improved FF of 74.31%, which is much higher than that of the devices based on reference FREAs without fluorination (8.21%) or conformation lock (12.48%). Our results demonstrate that enhancing phase separation with conformation-locked nonfullerene acceptor could be an effective way for further improving the related performance of OSCs.