Abstract:
The Platypus and Spatz neutron instruments are the time-of-flight neutron reflectometers at the CG3 and CG2B cold-neutron guide of the OPAL Reactor. The sample geometry of Platypus is a horizontal setup, which can further provide the free-liquid and polarization experiment. The sample setup on the Spatz reflectometer is vertical, and the FTIR spectroscopy can be performed while measuring the reflectivity. The reflectivity performance of both instruments can be achieved down to 10-7 with good counting statistics using a wavelength range of 2 to 20 Å. Neutron reflectivity has helped probe the vertical morphology of organic solar cells. PffBT4T-2OD and ITIC are utilized as donors and acceptors in a bulk heterojunction (BHJ) layer. The experiments aim to (1) Profile the vertical distribution of donor and acceptor phases in the blend film. Reveal the effect of donor-acceptor composition on the morphology change of the BHJ layer. (2) Understand the changes in vertical morphology through thermal annealing. The preferred molecular interaction, possibly initiated by the elevated temperature, generated a concentration gradient in the BHJ layer. These results will complement our other characterization techniques, such as AFM, GISAXS, and molecular dynamics simulation, assisting in developing efficient non-fullerene organic solar cells.