Enhanced Performance of a Self‐Powered Organic/Inorganic Photodetector by Pyro‐Phototronic and Piezo‐Phototronic Effects

Self‐powered photodetectors (PDs) have long been realized by utilizing photovoltaic effect and their performances can be effectively enhanced by introducing the piezo‐phototronic effect. Recently, a novel pyro‐phototronic effect is invented as an alternative approach for performance enhancement of self‐powered PDs. Here, a self‐powered organic/inorganic PD is demonstrated and the influences of externally applied strain on the pyro‐phototronic and the photovoltaic effects are thoroughly investigated. Under 325 nm 2.30 mW cm^‐2 UV illumination and at a ‐0.45% compressive strain, the PD's photocurrent is dramatically enhanced from ≈14.5 to ≈103 nA by combining the pyro‐phototronic and piezo‐phototronic effects together, showing a significant improvement of over 600%. Theoretical simulations have been carried out via the finite element method to propose the underlying working mechanism. Moreover, the pyro‐phototronic effect can be introduced by applying a ‐0.45% compressive strain to greatly enhance the PD's response to 442 nm illumination, including photocurrent, rise time, and fall time. This work provides in‐depth understandings about the pyro‐phototronic and the piezo‐phototronic effects on the performances of self‐powered PD to light sources with different wavelengths and indicates huge potential of these two effects in optoelectronic devices.     

Self‐Powered Si/CdS Flexible Photodetector with Broadband Response from 325 to 1550 nm Based on Pyro‐phototronic Effect: An Approach for Photosensing below Bandgap Energy

Cadmium sulfide (CdS) has received widespread attention as the building block of optoelectronic devices due to its extraordinary optoelectronic properties, low work function, and excellent thermal and chemical stability. Here, a self‐powered flexible photodetector (PD) based on p‐Si/n‐CdS nanowires heterostructure is fabricated. By introducing the pyro‐phototronic effect derived from wurtzite structured CdS, the self‐powered PD shows a broadband response range, even beyond the bandgap limitation, from UV (325 nm) to near infrared (1550 nm) under zero bias with fast response speed. The light‐induced pyroelectric potential is utilized to modulate the optoelectronic processes and thus improve the photoresponse performance. Lasers with different wavelengths have different effects on the self‐powered PDs and corresponding working mechanisms are carefully investigated. Upon 325 nm laser illumination, the rise time and fall time of the self‐powered PD are 245 and 277 µs, respectively, which are faster than those of most previously reported CdS‐based nanostructure PDs. Meanwhile, the photoresponsivity R and specific detectivity D* regarding to the relative peak‐to‐peak current are both enhanced by 67.8 times, compared with those only based on the photovoltaic effect‐induced photocurrent. The self‐powered flexible PD with fast speed, stable, and broadband response is expected to have extensive applications in various environments.     

Piezo‐Phototronic Effect on Selective Electron or Hole Transport through Depletion Region of Vis–NIR Broadband Photodiode

Silicon underpins nearly all microelectronics today and will continue to do so for some decades to come. However, for silicon photonics, the indirect band gap of silicon and lack of adjustability severely limit its use in applications such as broadband photodiodes. Here, a high‐performance p‐Si/n‐ZnO broadband photodiode working in a wide wavelength range from visible to near‐infrared light with high sensitivity, fast response, and good stability is reported. The absorption of near‐infrared wavelength light is significantly enhanced due to the nanostructured/textured top surface. The general performance of the broadband photodiodes can be further improved by the piezo‐phototronic effect. The enhancement of responsivity can reach a maximum of 78% to 442 nm illumination, the linearity and saturation limit to 1060 nm light are also significantly increased by applying external strains. The photodiode is illuminated with different wavelength lights to selectively choose the photogenerated charge carriers (either electrons or holes) passing through the depletion region, to investigate the piezo‐phototronic effect on electron or hole transport separately for the first time. This is essential for studying the basic principles in order to develop a full understanding about piezotronics and it also enables the development of the better performance of optoelectronics.     

Novel Transparent and Self‐Powered UV Photodetector Based on Crossed ZnO Nanofiber Array Homojunction

A novel self‐powered UV photodetector based on electrospun ZnO nanofiber arrays is introduced. Aligned pure ZnO nanofibers and Ag‐doped p‐type ZnO nanofibers are processed perpendicular to each other, and p–n junction arrays of ZnO nanofibers are fabricated as a result. Owing to the intrinsic intervals between nanofibers, the device is fully transparent on quartz substrate. Various characterization methods including TEM, XRD, and XPS are used to testify the existence form of Ag element in ZnO nanofibers, and a field effect transistor is constructed to judge their conductivity. It is discovered that the Ag doping process not only transforms ZnO to p‐type conductivity, making it possible to build this self‐powered photodetector, but also forms Ag nanoparticles in ZnO nanofibers and thus helps reduce the response time. Benefiting from the abovementioned dual effects, this UV detector is found to have an enhanced performance, with the on–off ratio up to 10⁴ at zero bias and a rather short rise/decay time of 3.90 s/4.71 s.     

Novel UV–Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction

A feasible strategy for hybrid photodetector by integrating an array of self‐ordered TiO₂ nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO₂ NTs and Se in combination with the surface trap states at TiO₂ help regulate the electron transport and facilitate the separation of photogenerated electron–hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W^?1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p‐type Se into TiO₂ NTs broadens the detection range to UV–visible (280–700 nm) with a large detectivity of over 10¹² Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈10⁷ A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 10⁴) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy‐efficient optoelectronic devices for practical applications.