Enhancing functionalities of organic ultraviolet-visible phototransistors incorporating spiropyran-merocyanine photochromic materials

Abstract

In this study, the multimode photoresponse (PR) features of low-voltage-driven pentacene-based organic phototransistors (OPTs) are reported by utilizing poly(4-vinylphenol) (PVP)-based gate dielectrics containing spiropyran-merocyanine (SP-MC) photochromic materials. In general, pentacene-based OPTs respond to visible light but cannot sense ultraviolet (UV) light. Incorporating SP-MC molecules provides pentacene-based OPTs with the functions of not only sensing UV light but also exhibiting different response modes to UV and visible light and thus can be used to distinguish UV and visible light sources. When the as-prepared OPTs are exposed to UV light, they can simulate the characteristics of typical paired-pulse facilitation and long-term potentiation properties as observed in photonic synaptic devices. The corresponding UV photovoltaic effects in the as-prepared OPTs are investigated in joint experimental measurements and theoretical calculations. We found large amounts of MC molecules in the prepared PVP:SP blend-based dielectrics in the dark, showing that pentacene-based OPTs have unique PR features in contrast to gate dielectrics that contained only SP. MC is an isoform of SP that is typically triggered by irradiation with UV light. Theoretical calculation results indicate that the MC form has large dipole moment features during photoexcitation and several charge transfer states exist, leading to easy separation of photogenerated charges. By contrast, SP does not have the above characteristics. Accordingly, a unique PR mechanism between UV and visible light of the present OPTs is drawn. Several distinct PR types of the as-prepared pentacene-based OPTs expand the functionality of the devices, enhancing their potential for further diverse applications.