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

ABSTRACT [1]Benzothieno[3,2‐b][1]benzothiophene (BTBT) and its tetraoxide derivative [1]benzothieno[3,2‐b]benzothiophene‐tetraoxide (BTBTOx 4 ) 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 PTz 2 ‐BTBT , PTz 2 ‐BTBTOx 4 , MPA 2 ‐BTBT , MPA 2 ‐BTBTOx 4 , POCz 2 ‐BTBT , and POCz 2 ‐BTBTOx 4 , designed as donor–acceptor–donor (D–A–D) structures. These compounds combine BTBT and BTBTOx 4 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. BTBTOX 4 ‐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.