Abstract
Morphology control in laboratory and industry setting remains as a major challenge for organic solar cells (OSCs) due to the difference in film-drying kinetics between spin coating and the printing process. A two-step sequential deposition method is developed to control the active layer morphology. A conjugated polymer that self-assembles into a well-defined fibril structure is used as the first layer, and then a non-fullerene acceptor is introduced into the fibril mesh as the second layer to form an optimal morphology. A benefit of the combined fibril network morphology and non-fullerene acceptor properties was that a high efficiency of 16.5% (certified as 16.1%) was achieved. The preformed fibril network layer and the sequentially deposited non-fullerene acceptor form a robust morphology that is insensitive to the polymer batches, solving a notorious issue in OSCs. Such progress demonstrates that the utilization of polymer fibril networks in a sequential deposition process is a promising approach towards the fabrication of high-efficiency OSCs.
Highlights
Morphology control in laboratory and industry setting remains as a major challenge for organic solar cells (OSCs) due to the difference in film-drying kinetics between spin coating and the printing process
Varied PT2 polymers are synthesized with different molecular weight and polydispersity values, and fibril network strategy (FNS)-sequential deposition (SD) processing leads to highly uniform device performance, solving the notorious batchto-batch variation problem in OSCs
Chloroform (CF) is chosen as the casting solvent for Y6 to swell the PT2 layer and assist Y6 molecules to diffuse into the fibril mesh. 1,8-diiodooctane (DIO) solvent additive and thermal annealing treatment were employed to further optimize the active layer morphology
Summary
Morphology control in laboratory and industry setting remains as a major challenge for organic solar cells (OSCs) due to the difference in film-drying kinetics between spin coating and the printing process. Controlling the BHJ morphology under different film-forming processes (the lab-scale spin coating versus industrial printing) remains challenging for the commercialization of OSCs. The two-step sequential deposition (SD) method provides an avenue to control the active layer morphology, in which the donor and the acceptor are deposited sequentially[31,32,33,34,35]. The swelling induced diffusion of second layer materials into the first one is highly manageable by choosing proper solvent and drying speed[35] Such a thin film fabrication, in couple with the proper first layer construction, can be highly useful in morphology control. Varied PT2 polymers are synthesized with different molecular weight and polydispersity values, and FNS-SD processing leads to highly uniform device performance, solving the notorious batchto-batch variation problem in OSCs
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