The effect of extended alkyl length on molecular orientation of nonfullerene acceptor: a case study in as-cast polymer solar cells

• The longer linear alkyl side chain decreased the absorption coefficient of molecule acceptors. • The shorter linear alkyl side chain is beneficial for the face-on molecular orientation. • Charge transfer and dynamics intimately correlate with bulk heterojunction interfacial. In this work, the effective electronic coupling on the indacenodithiophene (IDT)-based nonfullerene core was investigated by changing the length of the linear alkyl side chain. Extended linear alkyl side chain reduces the extinction coefficient in thin films and promotes the tendency of nonfullerene molecules to edge-on orientation. The theoretical calculation illustrates that the enhanced electronic coupling stem from short alkyl side chain could be beneficial for face-on orientation and charge transport. For the as-cast solar cells, the devices based on IDIC with the short alkyl side chain possessed the best efficiency. Our result manifests that the linear alkyl chain on the core of nonfullerene acceptor dominates molecular packing mode, light absorption, bulk heterojunction size, charge carrier transport and recombination dynamics.