Fig. 1. Different detectors^[23]. (a) Device structure of the PM-type photodetectors; (b) EQE spectrum of the photodetectors with PbS QDs under reverse bias from 0 to -7 V (inset: EQE under logarithmic coordinates); energy diagram of photodetectors under illumination (c) without and (d) with PbS QDs traps

Fig. 2. Photodetector doped with C₆₀ nanoparticles in the photosensitive layer^[25]. (a) Diagram of device structure; (b) energy level diagram of OPD

Fig. 3. Schematic images of interfacial barriers of PM-type OPD under reverse bias in dark and under illumination^[26]. (a) Without LiF interfacial layer; (b) with LiF interfacial layer

Fig. 4. Principle diagram^[29]. (a) Traditional OPDs under short-wavelength light illumination; (b) traditional OPDs under 650 nm light illumination; (c) PM-type OPD under short- wavelength light illumination; (d) PM-type OPD under 650 nm light illumination

Fig. 5. CIN narrowband photomultiplier^[31]. (a) Schematic structure diagram of the prepared OPD; (b) transmittance spectrum of Al films with different thickness; (c) EQE spectrum of the OPD with different thickness of Al electrode under bottom illumination condition at -20 V bias; (d) EQE spectrum of the corresponding OPD under top illumination condition at -20 V bias

Fig. 6. Capture hole^[47]. (a) Energy level diagram of OPD; (b) EQE spectrum of PM-type OPD under different reverse bias

Fig. 7. Schematic of UV light induced oxygen desorption from the surface of ZnO nanoparticles and the concomitant change in surface energy level structure and free electron density^[56]. (a) In the cases of pristine; (b) under UV light illumination and (c) after UV light treatment; (d) working mechanism of the OPD

Fig. 8. Working mechanism of the OPD^[58]. (a) In dark; (b) under illumination

Table 1. Major progress of PM-type OPDs