Efficient synthesis of dibenzopyran building block and its application in organic photovoltaics

• Dibenzopyran building block was efficiently synthesized.
• Branched alkoxy chains were introduced to benzothiadiazole.
• Two dibenzopyran based conjugated polymers were reported.
• DFT calculation was employed for understanding of the Uv–vis absorption behavior.

The efficient synthesis of the 3,8-dibromodibenzopyran building block was achieved by a series of high yielding reactions. By utilization of the final dibenzopyran, two donor-acceptor alternating conjugated polymers were synthesized and their photophysical and electrochemical properties were examined. In addition, the Uv–vis behavior of the polymers was also described by virtue of DFT calculations to further understand the origin of different absorption bands; efficient charge transfer was observed for the optical transitions from the ground states to excited states in natural transition orbitals. Photovoltaic properties were tested in polymer solar cells with dibenzopyran-based polymer:PC71BM as the active layer; this configuration demonstrated a power conversion efficiency of 2.88% with a high Voc of 0.92 V, a Jsc of 6.75 mA/cm2, and a comparable fill factor of 0.46.

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