Fig. 1. Schematic showing the concept of biodegradable and disposable UV photodetectors for smart textiles leaving no toxic residues.

Fig. 2. UV-visible spectroscopy studies. (a) Transmittance plot of chitosan with the optical image of the prepared chitosan film, and (b) absorbance plot of the ZnO NW with the inset showing the taucs plot with the calculated band gap. (c) Low and (d) high magnification SEM images of ZnO NWs.

Fig. 3. ZnO NWs based printed PD and electrical characterization results. (a) Schematic of the fabricated device. (b) Absolute current vs voltage plot. (c) Light illuminated temporal response characteristics at different bias voltages (1–5 V) under different UV illumination intensities. (d) Stepwise incremental response under different light intensities from 0.1 to 1.1 μW/cm². (e) Cyclic stability, and (f) linear dynamic response plot under different illumination intensities.

Fig. 4. (a) Responsivity. (b) Detectivity. (c) External quantum efficiency. (d) Response and recovery time. (e) Current on/off ratio. (f) Photoconductive gain of the photodetector at different bias voltages varying from 1 V to 5 V under different light intensities.

Fig. 5. Schematic representation of UV sensing under dark, explaining adsorption of oxygen from ambient air and formation of depletion layer and under illumination condition the electron-hole pair generation followed by the physical desorption and sensing mechanism explained with the help of energy band diagram for Ag/ZnO/Ag photodetector device.

Fig. 6. Temperature dependent performance stability data for ZnO NW printed PDs: (a) responsivity, (b) external quantum efficiency, (c) photoconductive gain, (d) detectivity, (e) on/off ratio, and (f) linear dynamic range of the device under different UV intensities.

Fig. 7. The temporal response characteristics of PD under different bending radii. (a) 40 mm, (b) 20 mm, (c) 10 mm and comparison of different performance parameters of the photodetector (d) responsivity, detectivity (e) gain, linear dynamic range (f) on/off ratio, EQE under different bending radius (note that 180° was considered as the device under flat condition).

Fig. 8. Biodegradability test of as fabricated device showing periodic degradability at different times in DI water. (a) 3 s showing absorption of water due to hydrophilic nature of chitosan. (b) Swelling of the chitosan after 60 s. (c) Physical disintegration after 5 min. (d) 80% of the device dissolved and (e) complete dissolution with only non-toxic screen-printed silver traces after 20 min. The outcome of dissolution tests repeated in PBS (pH=7.4) (f) after 10 s, (g) 10 min, (h) 30 min and (i) after an hour showing slight physical disruption of the device.