Design, synthesis, and structural characterization of the first dithienocyclopentacarbazole-based n-type organic semiconductor and its application in non-fullerene polymer solar cells

Ladder-type dithienocyclopentacarbazole (DTCC) cores, which possess highly extended p-conjugated backbones and versatile modular structures for derivatization, were widely used to develop high-performance p-type polymeric semiconductors. However, an n-type DTCC-based organic semiconductor has not been reported to date. In this study, the first DTCC-based n-type organic semiconductor (DTCC-IC) with a well-defined A-D-A backbone was designed, synthesized, and characterized, in which a DTCC derivative substituted by four p-octyloxyphenyl groups was used as the electron-donating core and two strongly electron-withdrawing 3-(dicyanomethylene) indan-1-one moieties were used as the terminal acceptors. It was found that DTCC-IC has strong light-capturing ability in the range of 500-720 nm and exhibits an impressively high molar absorption coefficient of 2.24 x 10(5) M-1 cm(-1) at 669 nm owing to effective intramolecular charge transfer and a strong D-A effect. Cyclic voltammetry measurements indicated that the HOMO and LUMO energy levels of DTCC-IC are x 5.50 and -3.87 eV, respectively. More importantly, a high electron mobility of 2.17-10(-3) cm(2) V-1 s(-1) was determined by the space-charge-limited current method; this electron mobility can be comparable to that of fullerene derivative acceptors (mu(e)-10(-3) cm(2) V-1 s(-1)). To investigate its application potential in non-fullerene solar cells, we fabricated organic solar cells (OSCs) by blending a DTCC-IC acceptor with a PTB7-Th donor under various conditions. The results suggest that the optimized device exhibits a maximum power conversion efficiency (PCE) of up to 6% and a rational high V-OC of 0.95 V. These findings demonstrate that the ladder-type DTCC core is a promising building block for the development of high-mobility n-type organic semiconductors for OSCs.