Film morphology evolution during solvent vapor annealing of highly efficient small molecule donor/acceptor blends
Sebastian Engmann, Hyun W. Ro, Andrew Herzing, Chad R. Snyder, Lee J. Richter, Paul Geraghty, David Jones
Solution-processable small molecule photovoltaics based on the novel molecular donor, benzodithiophene terthiophene rhodamine (BTR), recently have shown maximum power conversion efficiencies above 8% for active layer thicknesses up to 400 nm, using post process solvent vapor annealing (SVA) with tetrahydrofuran (THF). Here we report a in-situ study on the morphology evolution during SVA using the moderate solvent THF and the good solvent chloroform (CF). The combination of real-time grazing incidence X-ray diffraction (GIXD) and grazing incidence small angle X-ray scattering (GISAXS) allows us to draw a complete picture on the evolution of crystallinity and phase purity during post-process annealing. We find that the relative crystallinity is only modestly affected by SVA and solvent choice, when compared to the as-cast films. The characteristic domain sizes within the film, on the other hand, varies significantly and is controlled by the solvent quality as well as exposure time. Using THF, films with high phase purity and desirable characteristic length scales of about 30 nm can be achieved, while the use of CF rapidly leads to excessive film coarsening and less preferable domain sizes on the order of 60 nm, too large for optimized charge separation.
, Ro, H.
, Herzing, A.
, Snyder, C.
, Richter, L.
, Geraghty, P.
and Jones, D.
Film morphology evolution during solvent vapor annealing of highly efficient small molecule donor/acceptor blends, Journal of Materials Chemistry A, [online], https://doi.org/10.1039/C6TA05056E, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=920967
(Accessed November 28, 2023)