Suppression of Persistent Photoconductivity of Rubrene Crystals using Gate-Tunable Rubrene/Bi₂ Se₃ Diodes with Photoinduced Negative Differential Resistance

Organic single-crystalline semiconductors show great potential in high-performance photodetectors. However, they suffer from persistent photoconductivity (PPC) due to the charge trapping, which has severely hindered high-speed imaging applications. Here, a universal strategy of solving the PPC by integrating with topological insulator Bi₂ Se₃ is provided. The rubrene/Bi₂ Se₃ heterojunctions are selected as an example for general demonstration due to the reproducibly high mobility and broad optoelectronic applications of rubrene crystals. By virtue of high carrier concentration on Bi₂ Se₃ surface and the strong built-in electrical field, the photoresponse of the heterotransistor is significantly reduced for more than two orders (from over 10 s to 54 ms), meanwhile the photoresponsivity can reach 124 A W^-1 . To the best of knowledge, this operating speed is among the fastest responses in organic-inorganic heterojunctions. The heterotransistor also shows unique negative differential resistance under positive gate bias, which can be explained by photoinduced de-trapping of electron trap states in the bulk rubrene crystals. Besides, the rubrene/Bi₂ Se₃ heterojunction behaves as a gate-tunable backward-like diode due to the inhomogenous carrier distribution in the thick rubrene crystal and inversion of relative Fermi level positions. The findings demonstrate versatile functionalities of the rubrene/Bi₂ Se₃ heterojunctions for various emerging optoelectronic applications.