Epitaxial Perovskite Single-Crystalline Heterojunctions for Filter-Free Ultra-Narrowband Detection with Tunable Spectral Responses

Narrowband photodetectors (NPDs) with the capability of detecting light within a selective wavelength range are in high demand for numerous emerging applications such as imaging systems, machine vision, and optical communication. Halide perovskite materials have been developed for eliminating the current complex filtering systems in NPDs due to their beneficial properties, while currently NPDs using perovskite materials are limited by hardly fully eliminated short wavelength response, low charge collection efficiency (CCE), complex fabrication process, and so forth. Herein, a series of perovskite single-crystalline heterojunctions (PSCHs) with a structure of Bi-MAPbX3/MAPbY3 are fabricated by liquid phase epitaxy for filter-free narrowband detection. By varying the halide component in the PSCH, the PSCH-based NPDs can realize continuously tunable spectral response range from blue to NIR regions and ultra-narrow full width at half-maximum (FWHM) of <20 nm. Specifically, the PSCH-based NPD with a high CCE under a large electric filed shows a high spectra rejection ratio of >1000, a fast response speed with rise/fall time of ∼160/∼225 μs, and long-term stability more than 3 months in ambient air. This work provides a simple strategy for designing low-cost and high-performance filter-free NPDs with a tunable spectral response.

Double-Layered Strategy for Broadband Photomultiplication-Type Organic Photodetectors and Achieving Narrowband Response in Violet, Red, and Near-Infrared Light

Broadband photomultiplication-type organic photodetectors (PM-OPDs) were prepared with PMBBDT:PY3Se-2V (1:1, wt/wt) as the absorbing layer (AL) and PC₇₁BM:P3HT (100:5, wt/wt) as the photomultiplication layer (PML) on the basis of the sandwich structure. The incident photons from ultraviolet light to the near-infrared region can be harvested by AL. The rather less P3HT in PML can produce plenty of isolated hole traps with P3HT surrounded by PC₇₁BM; the electron tunneling injection induced by trapped holes near the Ag electrode can lead to the photomultiplication (PM) phenomenon. The performance of PM-OPDs can be effectively improved by optimizing the AL thickness. The optimal PM-OPDs exhibit a broad spectral response from 300 to 1050 nm as well as an external quantum efficiency (EQE) of 5800% at 340 nm at 10 V bias, along with a specific detectivity (D*) of 3.78 × 10¹³ Jones. The spectral response of PM-OPDs is controlled by the trapped-hole distribution near the Ag electrode, primarily originating from the photogenerated holes in AL. To further optimize the spectral response of PM-OPDs, the optical filter layer (OFL) was used to manipulate light field distribution in AL. The violet, red, and near-infrared-light PM-OPDs were developed by employing different OFLs.

Self-Driven Perovskite Narrowband Photodetectors with Tunable Spectral Responses

Narrowband photodetectors with tunable spectral responses are highly desirable for applications in image sensing, machine vision, and optical communication. Herein, a filterless and self-driven perovskite narrowband photodetector (PNPD) based on the defect-assisted charge collection narrowing (CCN) mechanism is reported, which is enabled by a high-quality thick perovskite film. By adjusting the halide component of the perovskite layer, the bandgap is successfully modulated and the corresponding narrowband photodetectors show a wide spectral response range from the red to the near-infrared (NIR), all with full-widths at half maximum (FWHMs) below 30 nm. Specifically, the methylammonium lead iodide (MAPbI₃ ) narrowband photodetector exhibits a characteristic detection peak at 800 nm with a very low noise current of ≈0.02 pA Hz^-1/2 , a high specific detectivity up to 1.27 × 10¹² Jones, and a fast response speed with rise/fall time of 12.7/6.9 µs. Impressively, these values are among the highest of their kind reported previously, and allow demonstration of narrowband imaging. The excellent performance of self-driven PNPDs lights up their prospect in high-efficiency optoelectronic devices without external power sources.

Filter-Free Selective Light Monitoring by Organic Field-Effect Transistor Memories with a Tunable Blend Charge-Trapping Layer

Integration of selective photodetection and signal storage in a single device, such as organic field-effect transistor (OFET) memories, meets the demands for radiation monitoring and protection. A new strategy is developed to achieve filter-free and selective light monitoring by adopting a solution-processed blend charge-trapping layer in OFET memories, where the charge-trapping layer is composed of phenyl-C₆₁-butyric acid methyl ester (PCBM) dispersed in a polymer electret thin film. The OFET memory without PCBM shows response only to ultraviolet light, whereas the spectral response edges are extended to the visible and near-infrared regions in the corresponding devices with relatively low and high contents of PCBM in the charge-trapping layer, respectively. A set of OFET memories with different PCBM contents is used to qualitatively evaluate the light composition in an optical source. The tunable spectral response in the OFET memories is ascribed to the additional photoassisted charge-trapping paths depending on the blend ratio in the charge-trapping layer. This mechanism may inspire alternative approaches to organic-based optical sensing and monitoring in flexible and wearable electronics.

Bias-Modulated High Photoelectric Response of Graphene-Nanocrystallite Embedded Carbon Film Coated on n-Silicon

We propose that bias-modulated graphene-nanocrystallites (GNs) grown vertically can enhance the photoelectric property of carbon film coated on n-Si substrate. In this work, GN-embedded carbon (GNEC) films were deposited by the electron cyclotron resonance (ECR) sputtering technique. Under a reverse diode bias which lifts the Dirac point of GNs to a higher value, the GNEC film/n-Si device achieved a high photocurrent responsivity of 0.35 A/W. The bias-modulated position of the Dirac point resulted in a tunable ON/OFF ratio and a variable spectral response peak. Moreover, due to the standing structured GNs keeping the transport channels, a response time of 2.2 μs was achieved. This work sheds light on the bias-control wavelength-sensitive photodetector applications.