摘要
Most polymer donors developed so far for high-performance non-fullerene OSCs are designed in planar molecular geometries containing BDT units. In this work, two donor-acceptor (D-A) conjugated polymers with wide band-gap, namely, PY3 and PY4, were designed and synthesized by introducing halogen atoms (F, Cl) into the donor units of polymers. We dismissed the pi-bridge and fused it to the A unit (BTz), presenting a different electron-deficient unit labeled as fused-DTBTz, forming a D-A structure with halogenated BDT units. PY3 with fluorine has a deeper HOMO level and a slight bathochromic-shift compared with PY4 with a chlorine atom, and shows good thermal stability among the two polymers. The reasonable halogenated D-unit in D-A polymers is beneficial for effectively promoting the intermolecular packing and crystalline properties, and thus enhancing the charge separation and transfer as reported previously. The best-performing PY3:IT-4Cl-based device afforded a high PCE of 11.20% with a V-OC of 0.798 V, a J(SC) of 19.09 mA cm(-2), and an FF of 73.5%, and the OSCs based on PY4:IT-4F delivered a PCE of 12.51%, with a noticeably elevated V-OC of 0.874 V, a J(SC) of 20.26 mA cm(-2), and an FF of 70.7%. The results showed that chlorinated polymers have a more suitable energy level to match the acceptors than their fluorinated counterparts, thus effectively improving the FF and J(SC) of photovoltaic devices. Therefore, there is much room for enhancement in photovoltaic properties with rational halogenation of the D moiety of D-A polymers.
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单位中国科学院青岛生物能源与过程研究所; 中国海洋大学