Structure Control during In Situ Printing of Donor-Acceptor Blend Films for Organic Solar Cells

Among the next generation solar cells, in particular organic photovoltaics are gaining impact as a promising alternative to conventional silicon-based solar cells. However, despite big achievements in terms of power conversion efficiencies in the last years, it remains an unresolved challenge to fabricate large-area organic solar cells without sacrificing efficiencies. The reason behind is that basic understanding is still very limited due to the complexity of the systems. Moreover, presently a substantial number of researchers use spin-coating for film deposition, which is not compatible with the needs of a large scale production. Thus, using up-scalable deposition methods such as printing are of immanent interest. [1] Large-area printing such as slot-die coating involves complex hydrodynamic processes and simply transferring optimized parameters from spin-coating studies has only limited success. Thus, in the present work, we use advanced scattering methods such as grazing incidence small and wide angle X-ray scattering (GISAXS and GIWAXS) in situ during printing of donor:acceptor blends to gain fundamental understanding about the underlying film formation processes. Different examples of polymer donors and small molecule acceptors are presented and the resulting morphologies are correlated with solar cell device performance. A special emphasis is put on the shift towards more environmentally friendly solvents, [2] which will be also a pre-requisite to promote a large-scale production of organic solar cells.<br/><br/>[1] Adv. Energy Mater. <b>13</b>, 2203496 (2023)<br/>[2] Adv. Mater. <b>32</b>, 2002302 (2020)