Influence of Acceptor Type and Polymer Molecular Weight on the Mechanical Properties of Polymer Solar Cells

Non-fullerene acceptors (NFAs), that are small-molecule acceptors (SMA) and polymer acceptors (PAs), have been extensively explored, which has yielded significant enhancements in the photovoltaic performance of polymer solar cells (PSCs). The mechanical robustness of the PSCs is of vital and equal importance to ensure the long-term stability and enable their use as power-generators in flexible and stretchable electronics. Here, we report a comparative study of the mechanical properties of SMA-based, PA-based, and fullerene-based PSCs. We chose ITIC (SMA), P(NDI2OD-T2) (PA), and PCBM (fullerene) as three representative acceptor materials and blended them with the same polymer donor PTB7-Th. To understand the difference between the mechanical properties of SMA-based and PA-based PSCs, we control the number-average molecular weight (Mn) of P(NDI2OD-T2) from 15 to 163 kg mol-1 in all-PSCs. The all-PSCs based high Mn PA exhibit significantly higher cohesion energy (4.03 J m-2) than SMA-PSCs (1.19 J m-2) and PC...