Fig. 1. The J–V characteristics of the devices in the dark or under illumination, and the schematic energy level diagram of the devices: (a) the device based on TiO₂ nanoparticles, (b) the device based on SnO₂ nanoparticles; the photoresponse of the devices: (c, e and g) the EQE, R, and D* of the TiO₂ device, respectively; (d, f and h) the EQE, R, and D* of the SnO₂ device, respectively.