The bulk-heterojunction morphology of organic solar cells is well recognized to be critical to the device performance and has received extensive research efforts in developing viable morphology tuning strategies. In this work, we present a morphology tuning approach for the molecular packing orientation, that is, through the ternary mixing of a donor polymer FTAZ with two distinctly oriented non-fullerene acceptors, IDIC and INIC3. By changing the incorporation concentration of INIC3, the originally bimodal oriented IDIC gradually reoriented to the dominant edge-on orientation. Remarkably, because of the strong backbone order induced from the end group π–π stacking of IDIC, ternary devices with strong edge-on order and appropriate phase separation domain sizes still exhibited good electron mobility in the out-of-plane direction. It suggests that the backbone order could bridge in-plane and out-of-plane electron transfer in the ternary devices, facilitating charge collection and suppressing bimolecular recombination.
Manuscript by Xiao et al. was accepted by ACS Appl. Energy Mater. 2020. https://pubs.acs.org/doi/full/10.1021/acsaem.0c01858