Flexible Narrowband Ultraviolet Photodetectors with Photomultiplication Based on Wide Band Gap Conjugated Polymer and...

Lightweight and flexible ultraviolet (UV) photodetectors (PDs) have wide applications and have attracted more attention. PDs using organic and inorganic nanocomposites as active layers with a photodiode configuration could achieve photomultiplication and narrowband photoresponse via the control of microstructure and thickness of active layers. Here, we fabricated flexible UV PDs on indium tin oxide-coated poly(ethylene terephthalate) substrates with a nanocomposite active layer composed of ZnO nanoparticles blended with a wide band gap conjugated polymer, poly[(9,9-dioctylfluorenyl-2,7-diyl)- alt- co-(bithiophene)] (F8T2). As a result of the wavelength-dependent penetration depth of light in the active layer, the fabricated flexible UV PDs showed two narrow response peaks at 360 and 510 nm under reverse biases in the external quantum efficiency (EQE) spectra with full width at half maximum (FWHM) less than 20 nm. Both responses exhibited greater than 100% EQE, indicating a photomultiplication effect, whereas the UV response at 360 nm was 10 times stronger under -15 V bias. The fabricated flexible UV PDs were bent under both tensile and compressive stress to a curvature of 2.1 cm^-1, each with 50 repetitions. The peak specific detectivity ( D*) only decreased by about 5% in total, the FWHM was well retained below 20 nm and the response speed remained almost constant after two types of bending, demonstrating mechanical flexibility and photoresponse stability of the fabricated flexible UV PDs. The photodiode configuration with nanocomposite active layers offers a promising route to make flexible and conformable narrowband, photomultiplication-type photodetectors for modern applications.