NIR absorbing tetracyanoquinodimethane-functionalized carbazole derivatives for highly efficient solution-processable organic photodetectors

Four tetracyanoquinodimethane derivatives with the different number and differently substituted ethylcarbazole donor moieties and nitrile groups are designed and synthesized. Ionization energies of the compounds are in the range of 5.25–5.52 eV. The compounds demonstrate moderate thermal stability with 5% weight loss temperatures in the range from 228 to 289 °C. The compounds exhibit broad absorption spectra with the optical bandgap values estimated from onsets of the absorption spectra of the films of the compounds in the range of 1.23–1.42 eV. A series of organic photodetectors (OPD) is developed utilizing the synthesized compounds as dopants in the different organic matrices. In comparison to OPDs utilizing commercial compounds as host materials, the OPDs using the previously reported by our group compound, a derivative of thiazolo[5,4- d ]thiazole and carbazole, exhibited a higher ratio of 9.2 × 10³ of the photocurrent density under solar irradiation at the reverse bias of −4 V to the dark current density. When the colored glass filter cut off the spectral range shorter than 715 nm, the ratio is of 1.77 × 10². The results demonstrate the potential of the tetracyanoquinodimethane derivatives for the application in optoelectronic devices operating in the NIR region.