Interface terminal group regulated organic phototransistors with tunable persistent and switchable photoconductivity

Abstract

With both light detection and intrinsic amplification functions, organic phototransistors have demonstrated promising applications, including photodetection and photomemory. To achieve excellent photoresponse and superior photogain, a common and effective strategy is to modulate the trapping effect with the purpose of reducing recombination or prolonging the lifetime of the photogenerated charge carriers. However, introducing trapping sites delicately is challenging and might sacrifice the response rate together with a typical persistent photoconductivity. Here, we demonstrate a facile strategy for achieving high photo-responsive organic phototransistors with both persistent and switchable photoconductivity features via interface terminal group regulation. By varying the terminate groups of self-assembled monolayer (SAMs) from the strong electron withdrawing group — F, neutral −CH₃ to electron donating −NH₂ on the dielectric surface, we realize both minority carrier trapping and majority carrier trapping in the organic phototransistor based on the C8-BTBT active layer. The electron withdrawing effect of F significantly enhances the minority carrier trapping process and yields a high photoresponsivity with a long-lasting persistent photoconductivity. In contrast, the electron donating group −NH₂ with a distinct majority carrier trapping ability causes switchable photoconductivity so that the photocurrent can rise pronouncedly and fully decay along with light on/off. Attractively, both cases can deliver high performance with photoresponsivities higher than 10⁴ A W⁻¹ together with a photosensitivity in the level of 10⁷ and a detectivity of approximately 10¹⁵–10¹⁶ Jones. Such a tunable, excellent photoresponse property enables the convenient exploration of organic phototransistors to satisfy different application requirements.