Plasmonic Aluminum Nanohole Arrays as Transparent Conducting Electrodes for Organic Ultraviolet Photodetectors with Bias-Dependent Photoresponse

Electrodes consisting of plasmonic Al nanohole arrays (Al-NHAs) were incorporated into organic ultraviolet (UV) photodetectors that exhibited bias-dependent photoresponse. Al-NHAs were designed by using three-dimensional finite-difference time-domain (3D-FDTD) simulations to produce strong UV absorbance in the active layer and enhanced internal electric field intensity. The nanosphere lithography fabricated Al-NHAs were incorporated into organic conventional devices, which produced two narrow response peaks under reverse bias and one broad response peak under forward bias, while ITO-based control devices can only produce two-peak photoresponse spectra. The bias-dependent photoresponse switching achieved by the Al-NHA-based devices is attributed to the plasmonic-enhanced internal electric field, which acts as a small forward bias and increases the driving force for hole diffusion. Conventional devices with planar Al electrodes and hole-only devices with both planar Al and an Al-NHA electrodes were also fabricated and evaluated to confirm the photoresponse mechanism. Plasmonic Al-NHA electrodes provide an approach for making ITO-free, flexible organic UV photodetectors with improved photoresponse and bias-dependent response tunability.