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 (V_OC) as well as suppressed energy loss (E_Loss) 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 E_Loss 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 V_OC of 0.97 eV.