Highly Sensitive Ultraviolet and Visible Wavelength Sensor Composed of Two Identical Perovskite Nanofilm Photodetectors

Filter-Less Color-Selective Photodetector Derived from Integration of Parallel Perovskite Photoelectric Response Units

Color-selective photodetectors (PDs) play an indispensable role in spectral recognition, image sensing, and other fields. Nevertheless, complex filters and delicate optical paths in such devices significantly increase their complexity and size, which subsequently impede their integration in smart optoelectronic chips for universal applications. This work demonstrates the successful fabrication of filter-less color-selective perovskite PDs by integrating three perovskite units with different photoresponse on a single chip. The variation in photoresponse is attributed to different quantities of SnO2 nanoparticles, synthesized through controlled ultrasonic treatment on the surface of the electron transportation layer SnS2, which selectively absorb short-wavelength light, thus increasing the relative transmittance of long-wavelength light and enhancing the photoresponse of the units to long wavelengths. By integrating any two units and deriving the formula for the wavelength to the responsivity ratio, a wavelength sensor is developed which can accurately identify incident light in the range of 400-700 nm with a minimum error <3 nm. Furthermore, the device integrating three units with different photoresponse can identify red, green and blue in polychromatic light to achieve color imaging with a relative error <6%. This work provides valuable insights into wavelength identification and color imaging of perovskite PDs.

Vertically Stacked Transparent Organic Photodetectors for Light Intensity-Independent Wavelength Recognition

Wavelength recognition is one of the important functions of photodetectors. However, wavelength recognition of the reported photodetectors generally depends on light intensity, which limits the practical applications. Here, a light intensity-independent wavelength recognition scheme based on vertically stacked transparent photodetectors is reported. By analyzing light intensity attenuation behavior in the multiple stacked photodetectors, the wavelength of incident light can be accurately determined. Due to the high transparency of the detectors, the multiple stacked detectors allow incident light to pass through. Meanwhile, since the attenuation coefficients at different wavelengths are attributed to the detector's absorption characteristics, the intensity of incident light and its wavelength can be determined by analyzing the attenuation coefficients measured through each stacked detector. Consistent wavelength values obtained at different light intensities verify the light intensity-independence of the multistacked detector system.

Flexible Stacked Perovskite Photodetectors for High-Efficiency Multicolor Fluorescence Detection

A flexible, multicolor detector based on stacked perovskite layers with graded band gaps was presented. Different perovskite layers generate a series of photocurrents corresponding to light intensities at different wavelengths. Experimentally, the flexible detector demonstrated acceptable long-term stability and temperature stability in the bending state. To demonstrate the advantages of the flexible multicolor detector in biological applications, a tubular-shaped multicolor fluorescence detector that embraces the sample cell was constructed. As a result, the detection limits of three kinds of CdTe quantum dots (QDs) with central wavelengths of 545, 625, and 730 nm were 0.52, 0.85, and 0.43 nM, respectively, which was significantly improved by more than 10 times compared to those of planar detectors. Additionally, the detector was able to detect three kinds of QDs simultaneously in a mixed solution, and the relative deviation was smaller than 10% compared to the preset concentration. These results demonstrate that the flexible stacked perovskite detector and the tubular-shaped detection configuration hold promise for the simultaneous fluorescent detection of multiple biomolecules.

A Simple-Structured Perovskite Wavelength Sensor for Full-Color Imaging Application

In this study, simple-structured wavelength sensors were developed by depositing two back-to-back Au/MAPbI₃/Au photodetectors on an MAPbI₃ single crystal. This sensor could quantitatively distinguish wavelengths. Further device analysis showed that both photodetectors possess entirely disparate optoelectronic properties. Consequently, the as-developed wavelength sensor could accurately distinguish incident-light wavelengths ranging from 265 to 860 nm with a resolution of less than 1.5 nm based on the relation between the photocurrent ratios of both photodetectors and the incident light wavelengths. Notably, a high resolution and wide detection range are among the optimum reported values for such sensors and enable full-color imaging. Furthermore, technology computer-aided design (TCAD) simulations showed that a mechanism involved in distinguishing wavelengths is attributed to the wavelength-dependent photon generation rate in MAPbI₃ single crystals. The high-performance MAPbI₃ wavelength sensor can potentially drive the research progress of perovskites in wavelength recognition and full-color imaging.

Spray-Coating Thick Films of All-Inorganic Halide Perovskites for Filterless Narrowband Photodetectors

A significant challenge facing perovskite narrowband photodetectors is making high-quality and thick enough films. Here, we report a facile one-step spray-coating approach to deposit cesium lead halide perovskite thick films for filterless narrowband photodetectors, which exhibited a specific detectivity of 2.43 × 10¹⁰ Jones at 655 nm with an fwhm of 25 nm. We demonstrated that both substrate temperature and deposition time during the spray-coating process are key factors that govern the thickness and morphology of perovskite films. The photodetection behavior was dependent on the film thickness, and the narrowband photoresponse was recorded at a 3.9 μm thickness. We discovered that the internal electric field also plays a critical role in determining the narrowband photoresponse behavior. A distinct photoresponse behavior was observed when respectively applying a reverse bias and a forward bias, which is ascribed to the trade-off between the charge-trapping effect and charge extraction under the internal built-in electric field in different biased conditions. Through changing the halogen composition of perovskites from CsPbCl₂Br to CsPbI₂Br, the peak position of the narrowband spectral photoresponse was observed to shift from 460 to 660 nm. This study not only offers a controllable spray-coating approach to develop thick perovskite films but also provides an important guidance for the rational design of filterless narrowband photodetectors for practical applications in industrial control, visual imaging, and biological sensing.

Achieving dual-color imaging by dual-band perovskite photodetectors coupled with algorithms

Dual-color or multispectral imaging based on conventional optical imaging techniques is suffering from the bottleneck of complex manufacturing and time consumption caused by multiple imaging. Herein, we develop a dual-color computational imaging system combining a vertically stacked dual-channel dual-band perovskite photodetectors (PDs) and the advanced Fourier imaging algorithm. Significantly, our imaging system bypasses the complex fabrication process of high-density dual-band PD arrays and is enabled to capture two high-resolution spectral images at the same time. Based on the experiments and simulations, we confirm that the spectral overlap of dual-band PDs will cause detrimental effect for color identification, and optimizing the bandwidth spectrum is beneficial for achieving much better spectral imaging. Moreover, we have further improved the imaging quality by increasing the sampling rate and suppressing current fluctuations. We suggest that these results provide important interesting insights for the development of advanced imaging systems, including IR imaging, THz imaging, multispectral/hyperspectral imaging, etc.