Side-Chain Engineering in ITIC Skeleton Enabling As-Cast Organic Solar Cells with Reduced Energy Loss and Improved Vertical Phase Distribution

Constructing binary organic solar cells (OSCs) with remarkable open-circuit voltage (VOC) as well as suppressed energy loss (ELoss) has been considered a promising strategy for breaking the efficiency bottleneck for OSCs. In this work, two novel chlorinated fused-ring electron acceptors were designed and synthesized through side-chain engineering, of which the rotation of end-capping groups on the indenedithiene [3,2-b] thiophene core was effectively restricted. Benefiting from the conformation lock, the IMC6–4Cl and IMC8–4Cl binary donor/acceptor (D/A) blend films realized more ordered molecular stacking and reduced Urbach energy, leading to lower ELoss of the devices. Moreover, the prolonged side chains in IMC8–4Cl inhibited excessive aggregation of the molecules and facilitated better miscibility with D18. Therefore, the D18:IMC8–4Cl blend films exhibited more rational D/A phase separation and reduced energy disorder. Eventually, the D18:IMC8–4Cl based devices achieved an exceptional power conversion efficiency of 13.99% and a decent VOC of 0.97 eV.