The advantage of dimethyl-2H-benzimidazole compared to the benzothiadiazole moiety of PCDTBT is to improve the solubility of the polymer while keeping the 1,2-quinoid form to lead coplanarity of the backbone. New random copolymers, to broaden the absorption range for the wider coverage of the solar spectrum, were synthesized by Stille coupling reactions to generate PCPPDTMBIs (or PCPPBBTMBIs). The solid films of PCPPDTMBIs show absorption bands with two maximum peaks at about 408-417 and 613-640 nm. The PCPPBBTMBIs show two maxima peaks at about 440-444 and 627-650 nm which are red-shifted about 5-30 nm as compared to PCPPDTMBIs caused by the introduction of bithiophene units. The device with PCPPBBTMBI7:PC 71BM blend demonstrated a V OC value of 0.64 V, a J SC value of 2.12 mA/cm 2, and a FF of 0.34, leading to the efficiency of 0.46%.
Bibliographical noteFunding Information:
This work was supported by Biomedical Treatment Technology Development Project (No. 2015M3A9D7067418) and Wearable Platform Materials Technology Center (WMC) funded by the National Research Foundation (NRF) of Korea Grant of the Korean Government (Ministry of Science, ICT and Future Planning) (No. 5662016R1A5A1009926). This research was also supported by Research and Business Development Program through the Korea Institute for Advancement of Technology(KIAT) funded by the Ministry of Trade, Industry and Energy(MOTIE) (grant number : N0002418), and Global Frontier Project (CISS-2011-0031870), funded by the Ministry of Science, ICT and Future Planning.
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