Transient Current Response for ZnO Nanorod-Based Doubly Transparent UV Sensor Fabricated on Flexible Substrate

We present the transient current response for a ZnO nanorod-based doubly transparent UV sensor. ZnO nanorods (ZNRs) are sandwiched between indium tin oxide (ITO) electrodes to make the device doubly transparent on a flexible polyethylene terephthalate (PET) substrate. The average ZNR length and diameter are 1.7 μm and 62 nm, respectively, and the ITO is perfectly sputtered upon ZNR surface. All the ZNRs are c-axis oriented perpendicular to the substrate with a typical hexagonal wurtzite ZnO structure. Photoluminescence spectra show a typical high-intensity peak near 375 nm and a broad peak in the visible region. UV sensing is confirmed by testing ZNR current–voltage characteristics and transient current response under UV on–off conditions for straight and inflexed ZNRs. The sensor shows a 2.3 times increase in current intensity under UV illumination at 4 V. The transient current shows a typical sinusoidal wave-like response with three prominent regions under constant voltage supply. The recovery time is almost five-times of the response time, which confirms the five-times faster boundary hole trapping in the sensor than their release on the flexible substrate. Also, the current intensity decreases for an unilluminated flexed device and increases for an UV-illuminated flexed device because of strain-induced ZNR piezotronic effects under flexible deformation.