Revealing Ambipolar Charge Transport in BTBT‐Based D–A–D Molecules via Photo‐MIS‐CELIV Measurements

[1]Benzothieno[3,2-b][1]benzothiophene (BTBT) and its tetraoxide derivative [1]benzothieno[3,2-b]benzothiophene-tetraoxide (BTBTOx4) are among the most interesting planar building blocks for constructing p-type and n-type transporting materials for organic optoelectronic devices. Herein, we report a study of six recently synthetized small molecules, namely PTz2-BTBT, PTz2-BTBTOx4, MPA2-BTBT, MPA2-BTBTOx4, POCz2-BTBT, and POCz2-BTBTOx4, designed as donor–acceptor–donor (D–A–D) structures. These compounds combine BTBT and BTBTOx4 as electron-accepting fused-ring cores with phenothiazine, bis(4-methoxyphenyl)amine, and 3,6-bis(4-(octyloxy)phenyl)-9H-carbazole as electron-donating end groups. The differences in electrochemistry, electronic molecular structures, and charge carrier mobilities of the six compounds are systematically studied. BTBTOX4-based compounds exhibit an ambipolar character and can serve as effective electron- and hole-transport materials for organic-based devices, showing also higher conductivity compared to the BTBT counterpart. On the contrary, the BTBT-based compounds show mainly a hole transport behavior but higher mobility.