Perovskite is an excellent photosensitive material but it exhibits a shortcoming in providing photoconductive gain for layered photodetectors due to lacking of trap states. Here, the perovskite photodetectors are fabricated with controllable photoconductive gain by designing a trapped‐electron‐induced hole injection structure of [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM):2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ)/Bathocuproine/Au. The deep trap states provided by F4‐TCNQ can capture the photogenerated electrons from perovskite, which makes the hole injection barrier thin enough to be tunneled through, allowing the hole injection and forming a gain. Meanwhile, the gain is controllable by adjusting the electron trapping and hole transport capacities of PCBM:F4‐TCNQ dual‐functional layer, concomitantly realizing the transition of device from photovoltaic to photoconductive. Thus fabricated device achieves a higher external quantum efficiency of 6 × 104% at a lower bias of −1 V, and simultaneously maintains the rectifying behavior in dark, providing the detectivity of about 1 × 1015 Jones.

An FTO/TiO 2 /MoO 3 based UV detector has been fabricated through the synthesis of TiO 2 nanowires (NWs) on FTO using the hydrothermal method, the preparation of MoO 3 on TiO 2 NWs by the spin-coating method, after the hydrothermal synthesis, and the preparation of Ag electrodes on the FTO and MoO 3 . The detector exhibits an excellent performance of photo-todark current ratio of more than two orders of magnitude. This performance is produced because the dark current under 2.2 V bias has been significantly inhibited due to the electronic potential well formed by the energy band distribution while the photocurrent has increased in comparison with FTO/TiO 2 based detectors under the same conditions which also have a higher photo-todark current ratio without the MoO 3 content. Not only does this study take advantage of 1D NWs and 2D nanostructures, but it also provides a new way to inhibit the dark current of detectors.

Applications of ZnO in photodetectors are limited by the great quantity of extrinsic majority carriers due to structural defects and difficult exciton dissociation due to the large exciton binding energy; these generally lead to a higher dark current (Id) and lower light current (Il), severely degrading the responsivity and detectivity. C dots are incorporated into an annealing-free ZnO layer to innovatively construct a local built-in electric field (Ebi) using the difference in the work functions; this simultaneously overcomes the drawbacks of the pristine ZnO photosensitive layer. In dark, the extrinsic majority carrier of ZnO is depleted around the incorporated C dots due to the self-depleting effect; thus, the Id decreases. Under UV illumination, the photogenerated exciton driven by the local Ebi is easily dissociated into a free charge carrier, contributing to the improved Il. This study paves a universal way to effectively improve the detection characteristics of photoconductive devices by incorporating the local Ebi.

TiO 2 has been widely used in ultraviolet (UV) photodetectors, but due to the large number of structural defects and strong band-to-band recombination of the exciton in TiO 2 , the devices usually have large dark current (I d ) and low light current (I l ), which seriously reduces the sensitivity and responsivity (R) of the TiO 2 based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO 2 film to ameliorate these issues. Due to the difference of work function between TiO 2 nanoparticles and C QDs, the built-in electric field (E bi ) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO 2 film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the I d of the photodetector. Moreover, the E bi and depletion region will also contribute to the faster charge collection under UV illumination and recombination of the electron in dark, which is beneficial for the improved response/recovery speed of the device.

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A visible-blind ultraviolet (UV) photodetector (PD) based on TiO/polyvinyl carbazole doped with poly {[2,7-(9-(20-ethylhexyl)-9-hexyl-fluorene])-alt-[5,50-(40,70-di-2-thienyl-20,10,30-benzothid-iazole)]} (PFTBT) was successfully fabricated. The introduced PFTBT exhibits high absorbance in the UV region and high conductivity which increases the device absorbance and the efficiency of carrier mobility. Besides, PFTBT acts as traps which can increase the concentration of the majority carrier. Therefore, the doped device exhibits high responsivity and high specific detectivity with the value of 0.22 A W and 1.78 × 10 Jones which respectively has a 3.6 and 2.6 times greater enhancement than the device without doping. The response time is also improved from 27 ms to 22 ms. Owing to the different absorbances that the materials have, the PD has a narrow detection range from 320 nm to 340 nm which is helpful to the study of the specific wavelength. In other words, the research provides a potential way to fabricate practical high-performance UVPDs.

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