Optimization of Crystallinity and Hole Mobility of BDT-Based Polymer Donor for Highly Efficient Nonfullerene Organic Solar Cells
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In this work, we develop a series of BDT-8ttTPD-based polymer donors to produce optimal crystallinity and hole mobility in nonfullerene organic solar cells. To overcome the amorphous characteristics of BDT unit, we employ planar 8ttTPD unit as a counterpart and moreover replace the hydrogen atoms attached to the third positions of side thienyl groups with halogen atoms to yield PBDT-X (X= H, F, and Cl). Synergistic effects of incorporated 8ttTPD unit and the halogenated 2D side chain generate significantly enhanced charge transport and recombination properties of the OSCs, which is mainly attributed to optimized crystallinity and hole mobility of the polymer donors. As a result, the PBDT-Cl:Y6 OSCs achieve the highest power conversion efficiency (PCE) of 15.63% with simultaneous improvements of open-circuit voltage, short-circuit current density, and fill factor, outperforming the PCEs of PBDT-H:Y6 (11.84%) and PBDT-F:Y6 (14.86%).