Multiwavelength Photodetectors Based on an Azobenzene Polymeric Ionic Liquid

Organic photodetectors (OPDs) are a promising class of light-detecting devices that can be created with simple fabrication techniques from a large variety of chemical building blocks. While molecular photoswitches are commonly used to modulate the properties of these devices through reversible isomerization or charge transfer, this responsive behavior is typically limited to a small range of wavelengths. Here, we report the characteristics of multiwavelength photodetectors using bilayers of a light-responsive azobenzene polymeric ionic liquid (PIL) in conjunction with the semiconducting polymer poly{(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophene-2,6-diyl)-alt-(2,3-difluoro-1,4-phenylene)} (PhF-2,3). Both ultraviolet (UV) and visible light induce a 102–103 increase in current at a constant voltage within 10 s, which decays immediately when the light is turned off. This light-mediated performance is fatigue-resistant across multiple ON/OFF cycles and can be modulated with wavelengths far into the visible region (660 and 700 nm). Frontier energy level calculations of the light-induced charge carrier density indicate that this light-responsive increase in current is due to photoexcitation and a subsequent charge-transfer process between the azobenzene polymeric ionic liquid and the semiconducting polymer. In summary, the device described in this report exhibits sensing capabilities for multiple wavelengths of light corresponding with the azobenzene absorption profile.