An n-Type All-Fused-Ring Molecule with Narrow Bandgap

All-fused-ring p-conjugated molecules have received considerable attention because of their unique electronic structures, low conformation disorder, and excellent optoelectronic properties. Most all-fused-ring molecules are p-type organic semiconductors and possess medium bandgaps. In this work, we design and synthesize an all-fused-ring molecule (FM1) with an n-type property and narrow bandgap, which is a 10-fused-ring system composed of one electron-deficient benzotriazole core, two electron-rich thienopyrrole bridging units, and two electron-deficient malononitrile-functionalized end-cappers. FM1 exhibits low-lying highest occupied molecular orbit/ lowest unoccupied molecular orbit energy levels of -5.77 eV/-3.89 eV, high electron mobility of 6.0 x 10(-4) cm(2) V-1 s(-1), an optical bandgap of 1.50 eV, and a maximum absorption wavelength of 769nm. Because of the all-fused-ring skeleton, FM1 shows superior photostability and chemical stability. We use FM1 as an electron acceptor and successfully construct organic solar cell (OSC) devices with a decent power conversion efficiency (PCE) of 10.8%. Most importantly, the intrinsic stability of FM1 leads to its excellent OSC device stability. After irradiation with simulated solar light for 16 h, while control of the OSC device of the state-of-the-art small molecule electron acceptor shows a 46% decrease of PCE, the FM1's unencapsulated OSC device exhibits only a 9% decrease of PCE.