Wavelength-Dependent Charge Carrier Dynamics for Single Pixel Color Sensing Using Graded Perovskite Structures

Self-Powered Wide-Narrow Bandgap-Laminated Perovskite Photodetector with Bipolar Photoresponse for Secure Optical Communication

Perovskite photodetectors with bipolar photoresponse characteristics are expected to be applied in the field of secure optical communication (SOC). However, how to realize the perovskite photodetector with bipolar response remains challenging. Herein, by introducing bismuth iodide (BiI3 ) into Sn-Pb mixed perovskite precursor solution, 2D perovskite FA3 Bi2 I9 is spontaneously formed at the bottom to realize a wide-narrow bandgap-laminated perovskite film. Wavelength-dependent bipolar response is realized based on the absorption difference of the photoactive region with different bandgap combined with the carrier competition of the homotypic transport layer adopted in the as-fabricated photodetector. Under the visible/near-infrared (NIR) light irradiation, the bottom/top of the film generates a higher carrier concentration, where electrons are easier to be separated and transported by the SnO2 /PC61 BM to the bottom/top electrodes, respectively, resulting in a negative and positive bipolar response. Finally, based on positive NIR signal as the effective signal and negative visible signal as the interference signal, the SOC system is realized, where the positive NIR signal is well hidden by the negative visible signal. This work provides a simple and feasible strategy for fabrication of laminated perovskite films to achieve bipolar response.

Self-Powered Wavelength-Dependent Dual-Polarity Response Photodetector Based on CdS@PEDOT:PSS@Au Sandwich-Structured Core-Shell Nanorod Arrays

Self-powered operation and multifunctionality have significantly oriented the development of photodetectors (PDs), which could be realized through nanoarchitecture construction and energy band structure design. Herein, a self-powered wavelength-dependent dual-polarity response PD based on (CdS@PEDOT:PSS@Au) sandwich-structured core-shell nanorod arrays (NRAs) is proposed. The synthesis approach of this three-layer heterostructure consists of a hydrothermal reaction, spin coating, and thermal evaporation. The n-CdS/p-PEDOT:PSS junction and the PEDOT:PSS/Au Schottky junction at the interfaces provide two photocurrent driving forces in opposite directions, and their contribution to the net photocurrent is controlled by the incident light wavelength due to the different light absorption ranges of the CdS core and the PEDOT:PSS shell. As a result, the polarity of the photocurrent switches from negative to positive as the wavelength increases. In addition, the response speed of negative photocurrents (∼10 ms) is faster than that of positive photocurrents (∼100 ms), which is consistent with the underlying mechanism of the dual-polarity response. Furthermore, color discrimination and imaging capabilities are demonstrated by deploying the PDs as sensing pixels and recognizing green and red patterns. The sandwich-structured core-shell NRA heterojunction system introduces a novel idea for dual-polarity response PDs.

Photosensitive Dielectric 2D Perovskite Based Photodetector for Dual Wavelength Demultiplexing

Stacked 2D perovskites provide more possibilities for next generation photodetector with more new features. Compared with its excellent optoelectronic properties, the good dielectric performance of metal halide perovskite rarely comes into notice. Here, a bifunctional perovskite based photovoltaic detector capable of two wavelength demultiplexing is demonstrated. In the Black Phosphorus/Perovskite/MoS₂ structured photodetector, the comprehensive utilization of the photosensitive and dielectric properties of 2D perovskite allows the device to work in different modes. The device shows normal continuous photoresponse under 405 nm, while it shows a transient spike response to visible light with longer wavelengths. The linear dynamic range, rise/decay time, and self-powered responsivity under 405 nm can reach 100, 38 µs/50 µs, and 17.7 mA W^-1 , respectively. It is demonstrated that the transient spike photocurrent with long wavelength exposure is related to the illumination intensity and can coexist with normal photoresponse. Two waveband-dependent signals can be identified and used to reflect more information simultaneously. This work provides a new strategy for multispectral detection and demultiplexing, which can be used to improve data transfer rates and encrypted communications. This work mode can inspire more multispectral photodetectors with different stacked 2D materials, especially to the optoelectronic application of the wide bandgap, high dielectric photosensitive materials.

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.

A Single-Dot Perovskite Spectrometer

There are significant applications for miniature on-chip spectrometers in many fields. However, at present, on-chip spectrometers have to utilize an integrated strategy to achieve spectral analysis, which undoubtedly squanders the photosensitive area and adds pressure to the miniaturization of the spectrometer. Here, a unique spectrometer design that adopts a single detection point with in situ modulation realized by the photogain control at various bias voltages is demonstrated. With micrometer-level footprints, this single-dot spectrometer processes a resolution of about 5 nm and a response time down to about 197 µs. This is the first in situ perovskite modulation strategy that breaks the footprint-resolution restriction of spectrum analysis and demonstrates a new design direction for functional perovskite devices.

van der Waals Semiconductor Empowered Vertical Color Sensor

Biomimetic artificial vision is receiving significant attention nowadays, particularly for the development of neuromorphic electronic devices, artificial intelligence, and microrobotics. Nevertheless, color recognition, the most critical vision function, is missed in the current research due to the difficulty of downscaling of the prevailing color sensing devices. Conventional color sensors typically adopt a lateral color sensing channel layout and consume a large amount of physical space, whereas compact designs suffer from an unsatisfactory color detection accuracy. In this work, we report a van der Waals semiconductor-empowered vertical color sensing structure with the emphasis on compact device profile and precise color recognition capability. More attractive, we endow color sensor hardware with the function of chromatic aberration correction, which can simplify the design of an optical lens system and, in turn, further downscales the artificial vision systems. Also, the dimension of a multiple pixel prototype device in our study confirms the scalability and practical potentials of our developed device architecture toward the above applications.

Beyond Tristimulus Color Vision with Perovskite-Based Multispectral Sensors

In this study, optical multispectral sensors based on perovskite semiconductors have been proposed, simulated, and characterized. The perovskite material system combined with the 3D vertical integration of the sensor channels allow for realizing sensors with high sensitivities and a high spectral resolution. The sensors can be applied in several emerging areas, including biomedical imaging, surveillance, complex motion planning of autonomous robots or vehicles, artificial intelligence, and agricultural applications. The sensor elements can be vertically integrated on a readout electronic to realize sensor arrays and multispectral digital cameras. In this study, three- and six-channel vertically stacked perovskite sensors are optically designed, electromagnetically simulated, and colorimetrically characterized to evaluate the color reproduction. The proposed sensors allow for the implementation of snapshot cameras with high sensitivity. The proposed sensor is compared to other sensor technologies in terms of sensitivity and selectivity.

Enhancing the photodetection performance of MAPbI3 perovskite photodetectors by a dual functional interfacial layer for color imaging

The color imaging capacity of recently developed perovskite photodetectors (PDs) has not been fully explored. In this Letter, we fabricate a CH₃NH₃PbI₃ (MAPbI₃) PD as a color imaging sensor mainly due to its almost flat spectral response in a full visible light region. To enhance the photodetection performance, we introduce a dual functional interfacial TiO₂ layer by atomic layer deposition, reducing the dark current to 12 pA from 13 nA and improving the photocurrent to 1.87 µA from 20 nA, resulting in a ∼10⁵ fold enhancement of the ON/OFF ratio. Since we obtained satisfactory color images, we believe that the MAPbI₃ perovskite PD is an ideal photosensitive device for color imaging.

Perovskite Color Detectors: Approaching the Efficiency Limit

Color image sensing by a smartphone or digital camera employs sensor elements with an array of color filters for capturing basic blue, green, and red color information. However, the normalized optical efficiency of such color filter-based sensor elements is limited to only one-third. Optical detectors based on perovskites are described, which can overcome this limitation. An efficient color sensor design has been proposed in this study that uses a vertically stacked arrangement of perovskite diodes. As compared to the conventional color filter-based sensors, the proposed sensor structure can potentially reach normalized optical efficiency approaching 100%. In addition, the proposed sensor design does not exhibit color aliasing or color Moiré effects, which is one of the main limitations for the filter-based sensors. Furthermore, up to our knowledge, for the first time, it could be theoretically shown that both vertically arranged sensor and conventional color filter-based sensor provide almost comparable color errors. The optical properties of the perovskite materials are determined by optical measurements in combination with an energy shift model. The optics of the stacked perovskite sensors is investigated by threedimensional finite-difference timedomain simulations. Finally, colorimetric characterization was carried out to determine the color error of the sensors.