Molecular aggregation and crystallinity control enables improved performance of all-polymer solar cells

Abstract

Manipulating the molecular aggregation and crystallization behavior of polymer acceptors (PAs) is one of the most important challenges for all-polymer solar cells (all-PSCs). In this work, we combine the advantages of a random ternary copolymerization strategy and fused perylene diimide dimer (FPDI) to synthesize a series of random copolymers (PNDI-FPDIX) for tuning and optimizing the self-aggregation of a prototypical PA (N2200). Specifically, FPDI with a quasi-two-dimensional structure was used as the guest acceptor unit to modify N2200 by substituting a certain amount of naphthalene diimide (NDI) acceptor unit, which not only regulates the optoelectronic properties but also alters the film morphology of the resultant random copolymers. The prepared PTzBi:PNDI-FPDI10 blend with 10% of the NDI monomers replaced by FPDI resulted in an excellent power conversion efficiency of 8.21% with an open-circuit voltage of 0.84 V, a short circuit current density of 14.81 mA cm⁻², and a fill factor of 66.03%. This work demonstrates that the aggregation behavior of PAs and thus efficiency of all-PSCs can be controlled by rationally selecting the guest component to construct random copolymers.