Organic photodetectors (OPDs) have attracted wide attention from researchers on account of their characteristics such as easy to manufacture, low cost, lightweight, and flexible detectors. Many efforts have been made to improve the performance of OPDs. Scientists have made many efforts to improve the performance of organic photodetectors. Among them, narrow-band-gap organic photoelectric functional materials with wide spectral response exhibit application prospects in photoelectric detection. In this paper, a series of narrow-band-gap thienoisoindigo receptor small molecules were synthesized by using thienoisoindigo, and electron deficient terminal octyl cyanoacetate, 3-ethylrhodanine, and 2-(3-ethyl-4-oxothiazolidine-2-ylidene) malonitrile as receptor units, and 3-dodecylthiophene as donor unit, The photodetector with wide spectral response and high detection rate is fabricated using a Bulk Heterojunction (BHJ) structure.