Structural Engineering of Nano-Grain Boundaries for Low-Voltage UV-Photodetectors with Gigantic Photo- to Dark-Current Ratios

Ultraporous networks of ZnO nanoparticles (UNN) have recently been proposed as a highly performing morphology for portable ultraviolet light photodetectors. Here, it is shown that structural engineering of the nano-particle grain boundaries can drastically enhance the performance of UNN photodetectors leading to gigantic photo to dark current ratios with operation voltages below 1 V. Ultraporous nanoparticle layers are fabricated by scalable low-temperature deposition of flame-made ZnO aerosols resulting in highly transparent layers with more than 95% visible light transmittance and 80% UV-light absorption. Optimal thermally induced necking of the ZnO nanoparticles increased the photo- to dark-current ratio, at a low light density of 86 mu W cm(-2), from 1.4 x 10(4) to 9.3 x 10(6), the highest so far reported. This is attributed to the optimal interplay of surface depletion and carrier conduction resulting in the formation of an open-neck grain boundary morphology. These findings provide a robust set of guiding principles for the design and fabrication of nanoparticle-based optoelectronic devices.