An experimental and theoretical study of the structural ordering of the PTB7 polymer at a mesoscopic scale

Our extensive study based on optoelectronic and electric measurements (which consisted of: UV–Vis absorption, photoluminescence, surface photovoltage measurement, charge extraction by linearly increasing voltage, and energy-resolved electrochemical impedance spectroscopy) revealed the fundamental role of the thickness of the formation of intra- and interchain interaction in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) films. We have shown that the final optoelectronic and electronic properties of PTB7 films are governed by the structural ordering development of the transition from nano-to submicroscale. The ordering of polymer chains and competition between the formation of J- and H-aggregates results in a non-trivial dependence of luminescence, exciton diffusion length, transport band gap, and defect concentration. According to a theoretical analysis, the driving forces responsible for the observed phenomena are associated with the thickness threshold dependence of the thin film drying mode which can proceed with or without the polymer skin formation on the surface of forming film. © 2019 Elsevier LtdMinistry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504]; Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF); national budget of the Czech Republic [CZ.1.05/2.1.00/19.0409]; Internal Grant Agency of TBU [IGA/CPS/2016/007, IGA/CPS/2017/008, IGA/CPS/2018/007]; Scientific Grant Agency VEGA [2/0081/18]; Slovak Research and Development Agency [APVV SK-CN-RD-18-0006]; [SVV 260 444/2018