Multi-scale mechanical properties of bulk-heterojunction films in polymer solar cells

The mechanical properties of bulk-heterojunction (BHJ) films play critical roles in the operational stability of flexible polymer solar cells (PSCs). In this study, the multi-scale mechanical properties of the BHJ films containing three representative electron acceptors are systematically evaluated. Interestingly, the tensile moduli of the films based on PC71BM, Y6, and PRi-C39 decrease sequentially, and their fracture strain and toughness show an increasing trend. Moreover, the nanoindentation moduli of the films based on these acceptors vary in accordance with the results of tensile characterizations. Creep analyses illustrate that the occurrence of creep deformation in the PC71BM, Y6, and PRi-C39-based films decrease sequentially. Contact angle tests demonstrate that the donor-acceptor interactions greatly affect the mechanical properties of these films. All results above demonstrate the effects of acceptor type on the multi-scale mechanical properties of the BHJ films, which are important for the development of reliable flexible PSCs.

Automated summary

This study systematically evaluates the multi-scale mechanical properties of bulk-heterojunction (BHJ) films containing three representative electron acceptors. It is found that the films based on PC71BM, Y6, and PRi-C39 show sequential decreases in tensile modulus and increases in fracture strain and toughness. The nanoindentation moduli of the films based on these acceptors also vary accordingly. Creep analyses reveal a sequential decrease in creep deformation occurrence for the PC71BM, Y6, and PRi-C39-based films. Contact angle tests demonstrate that donor-acceptor interactions greatly affect the mechanical properties of these films. These findings highlight the importance of acceptor type in the multi-scale mechanical properties of BHJ films for the development of reliable flexible polymer solar cells (PSCs).