A–D–A-type symmetric organic semiconductor for high performance self-powered photodiodes

Abstract In this study, an organic semiconductor material with a symmetric structure containing two diaminomaleonitrile units as electron acceptors and a central-thiophene skeleton as the electron donor was designed for photodiode applications based on acceptor–donor–acceptor architecture. The organic material, named ThPhAM6, was synthesized in excellent yield (98%) through a four-step process and thoroughly characterized using 1 H NMR, 13 C NMR, FTIR, and mass spectrometry techniques. The optical properties of ThPhAM6 thin films were investigated using UV-Vis absorption spectroscopy, while surface morphology analysis via scanning electron microscopy revealed nanostructured features favorable for efficient charge transport. To evaluate its device potential, the ThPhAM6 films were deposited on n-type silicon substrates to create organic–inorganic heterojunction photodiodes. The electrical and optoelectronic properties of the device were investigated under dark and illuminated conditions using a standardized white light source (1 sun, 100 mW cm −2 ) and ultraviolet illumination at 365 nm and 395 nm (23.5 mW cm −2 ). Under all illumination conditions, the device exhibited good rectifying behavior, a noticeable photovoltaic response, and self-powered operation without external bias. In particular, the highest performance was achieved under 395 nm UV illumination, where key metrics such as responsivity, specific detectivity, external quantum efficiency, noise equivalent power, and normalized photo-to-dark current ratio were determined. These results demonstrate that ThPhAM6 holds considerable promise for integration into next-generation UV photodetectors and energy harvesting technologies.