Study of Fracture and Tensile Properties of All-Polymer and Fullerene-Polymer Solar Cells Based on Same Polymer Donor

The mechanical properties of the polymer solar cells (PSCs) are important for their applications as flexible and wearable devices. In this work, we compare the mechanical properties including both fracture and tensile properties of all-polymer solar cells (all-PSCs) and PCBM-PSCs based on same polymer donor. First, we measured the fracture energy of two different PSCs using double cantilever beam (DCB) test. Surprisingly, the all-PSCs showed much higher fracture energy of 2.45 J m⁻² than that (0.29 J m⁻²) of PCBM-PSCs and the value of the all-PSCs was not dependent on the acceptor contents. Next, we examine the tensile properties of all-PSCs and PCBM-PSCs using pseudo free-standing test. Interestingly, 20-fold enhancement in elongation at break was observed in all-PSCs compared to that in PCBM-PSCs. This is because a large degree of plastic deformation occurred in all-PSCs due to polymer bridging in film during crack growth, in contrast to very weak interface between polymer and highly crystalline PCBM domains for the PCBM-PSCs. Therefore, our work suggests that replacing PCBM with polymer acceptor can be an effective strategy to obtain mechanically more robust PSCs.