Synthesis and characterization of new asymmetric thieno[3,4-b]pyrazine-based D−π−A−A type small molecular donors with near-infrared absorption and their photovoltaic applications

• Published in: Organic electronics Vol. 68; pp. 159 - 167
• Main Authors: Chou, Shu-Hua, Chen, Hsieh-Chih, Wang, Chun-Kai, Chung, Chin-Lung, Hung, Chieh-Ming, Hsu, Jung-Chun, Wong, Ken-Tsung
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2019
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2019.02.013

Two new asymmetric D−π−A1−A2 configured small molecules named PTP and TTP bearing thieno[3,4-b]pyrazine (TP) unit as the A1 group have been designed and synthesized for solution-processed bulk-heterojunction organic solar cells (OSCs). These new dipolar molecular donors not only exhibit strong near-IR absorption but pack into antiparallel dimers, in which PTP shows a coexistence of coplanar and cofacial antiparallel dimers configuration, while TTP reveals a coplanar centrosymmetric dimer structure. Solution-processed OSCs for PTP blended with pristine C70 achieves a promising power conversion efficiency (PCE) of 3.40% along with an open-circuit voltage (VOC) of 0.64 V, a short-circuit current density (JSC) of 9.83 mA cm−2 and a fill factor (FF) of 54.0%, which is the highest efficiency to date among the TP-based materials. Conversely, the optimized TTP:C70 solar cell delivers a VOC of 0.48 V, a JSC of 6.02 mA cm−2 and a FF of 43.3%, corresponding to a moderate PCE of 1.25%. [Display omitted] •New bipolar small molecule donors (PTP and TTP) configured with D−π−A1−A2 architecture, where thieno[3,4-b]pyrazine (TP) serves as the A1 group to link triarylamine (D−π) and dicyanovinylene (A2).•These new donors exhibit antiparallel dimeric pair crystal packing and strong near-IR absorption that are suitable for solution-processed bulk-heterojunction organic solar cells (OSCs).•With pristine C70 as acceptor, phenylene-bridged PTP donor achieved power conversion efficiency (PCE) of 3.40%, whereas the strong N-IR absorption donor TTP gave a PCE of 1.25%.•The superior performance of PTP-based OSC is in line with the higher hole mobility, better bicontinuous interpenetrating morphology and stronger (010) π–π stacking peak in the out-of-plane direction.