Improvement in power conversion efficiency of all-polymer solar cells enabled by ultrafast channels for charge dynamics

Abstract Despite the rapid breakthrough of polymerized fused-ring small molecular acceptors, developing accessible and inexpensive polymer acceptors for high performance all-polymer solar cells (all-PSCs) and revealing the fundamental work mechanism of all-PSCs is highly desirable. In addition, the isomeric issue of polymerized fused-ring small molecular acceptors still needs to be concerned. In this work, we report an accessible and inexpensive polymer acceptor P2TF by polymerization of 2,2'-((2Z,2Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno [1,2-b:5,6-b']dith-iophene-2,7-diyl)bis (me-thanylylidene))bis (3-oxo-2,3-dihydro-1H-indene-2,1-diylide-ne)) dimalononitrile-based small molecular. Molecular electrostatic potentials and permanent dipole moments are evaluated by theoretical calculations, revealing that structural isomerization has a negligible impact on their optoelectronic properties. Femtosecond-resolved transient absorption, device charge dynamic measurements and space-charge limited current method are performed to systematically investigate charge dynamics in all-PSCs. The PM6:P2TF-based as-cast device exhibits poor power conversion efficiency of 4.51%, while the optimized device achieves a superior power conversion efficiency of 10.65%. The significantly improved performance of the optimized device originates from ultrafast channels of charge dynamics for ultrafast charge transfer, efficient charge transport and suppressed charge recombination, which is strongly related to the well-established morphology induced by optimal treatment. Furthermore, the PM6:P2TF also has excellent bending property, indicating its great potential for application in flexible all-PSCs.