Wide bandgap conjugated polymers based on bithiophene and benzotriazole for bulk heterojunction solar cells: Thiophene versus thieno[3,2-b]thiophene as π-conjugated spacers

ABSTRACT

Two wide bandgap (WBG) conjugated polymers, P2T-DTTTAZ and P2T-DTTAZ, with donor-π-acceptor (D-π-A) structures was designed and synthesized, utilizing thieno[3,2-b]thiophene (TT) and/or thiophene (T) units as π-bridge in conjugated polymer backbone. And, the wider optical band gap (E_g) of approximately 1.98 eV for P2T-DTTTAZ and 2.09 eV for P2T-DTTAZ were observed. Obviously, replacing T unit with larger conjugated plane TT unit as π-bridges, P2T-DTTTAZ resulted in the red shifted absorption and the reduced band gap, compared with these of P2T-DTTAZ. The polymer solar cells (PSCs) with an inverted device structure based on P2T-DTTTAZ or P2T-DTTAZ as donor and [6,6] phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) as acceptor were assembled and the photovoltaic properties were also investigated. The power conversion efficiencies (PCEs) of 1.57% for P2T-DTTTAZ and 1.25% for P2T-DTTAZ were obtained.

KEYWORDS:

• Wide bandgap
• thiophene
• thieno[3,2-b]thiophene
• conjugated polymer
• photovoltaic propertites

Acknowledgements

The authors are deeply grateful to National Natural Science Foundation of China (No: 61404067, 51463011, 51602139); the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-13-0840), the foundation of A Hundred Youth Talents Training (152022) and Excellent Scientific Research Platform Supporting Program of Lanzhou jiaotong University for financial supports.