Frequency- and Power-Dependent Photoresponse of a Perovskite Photodetector Down to the Single-Photon Level

Spontaneous Cooling Enables High-Quality Perovskite Wafers for High-Sensitivity X-Ray Detectors with a Low-Detection Limit

Developing high-quality perovskite wafers is essential for integrating perovskite technology throughout the chip industry chain. In this article, a spontaneous cooling strategy with a hot-pressing technique is presented to develop high-purity, wafer-scale, pinhole-free perovskite wafers with a reflective surface. This method can be extended to a variety of perovskite wafers, including organic-inorganic, 2D, and lead-free perovskites. Besides, the size of the wafer with diameters of 10, 15, and 20 mm can be tailored by changing the mold. Furthermore, the mechanism of spontaneous cooling for improving the quality of perovskite wafers is revealed. Finally, the high-quality lead-free Cs3Cu2I5 perovskite wafers demonstrate excellent X-ray detection performances with a high sensitivity of 3433.6 µC Gyair -1 cm-2 and a low detection limit of 33.17 nGyair s-1. Moreover, the Cs3Cu2I5 wafers exhibit outstanding environmental and operational stability even without encapsulation. These research presents a spontaneous cooling strategy to achieve wafer-scale, high-quality perovskites with mirror-like surfaces for X-ray detection, paving the way for integrating perovskites into electronic and optoelectronic devices and promoting the practical application of perovskite X-ray detectors.

Surface Microstructure Engineering in MAPbBr3 Microsheets for Performance-Enhanced Photodetectors

Metal halide-perovskite-based photodetectors have recently emerged as a class of promising optoelectronic devices in various fields. Meanwhile, nano/microstructuring perovskite-based photodetectors are a facile integration with complementary metal-oxide semiconductors for miniaturized imaging systems. However, there are still challenges to be overcome in reducing the losses caused by light reflection on the surface of microstructural perovskites. In this work, surface microstructure engineering is employed in MAPbBr3 microsheets for reducing light reflection and improving light absorption, resulting in high-performance perovskite photodetectors. MAPbBr3 microsheets, which possess different surface morphologies of flat, upright hemisphere arrays and inverted hemisphere arrays (IHAs), are fabricated by a simple microstructure template-assisted space confinement process. The light absorption capacity of IHA MAPbBr3 is significantly higher than that of the other two structures. Hence, IHA photodetectors with excellent figures of merit, including low dark current, decent responsivity, and fast speed, are achieved. Furthermore, the noise of the IHA photodetectors is only ∼10-13 A/H z , which results in the superior sensitivity for weak light detection with a specific detectivity up to 1011 Jones. Our results demonstrate that surface engineering is a simple, low-cost, yet effective approach to improve the performance of nano-/micro-optoelectronic devices.

2D/3D Perovskite Photodetectors with High Response Frequency and Improved Stability Based on Thiophene-2-ethylamine and Dual Additives

Organic-inorganic lead halide perovskite materials have received great attention in recent years. However, the poor stability of these materials severely limits the commercial application of perovskite devices. Here, we used thiophene-2-ethylammonium iodide (TEAI) material as the organic spacer NH₄SCN and NH₄Cl as the dual additives to realize high-stability two-dimensional (2D)/three-dimensional (3D) perovskite thin films for perovskite photodetectors. Then, we investigated different effects of the dual additives on the orientation and crystallinity of the perovskite films. At room temperature, the optimized 2D/3D perovskite photodetectors exhibit good performance with high external quantum efficiency (EQE) (72%), large responsivity (0.36 A/W), high detectivity (2.46 × 10¹² Jones at the bias of 0 V), high response frequency (1.7 MHz), and improved stability (retains 90% photocurrent after 2000 h storage in RT and 10% RH conditions). Based on these devices, a dual-channel optical transport system and a light-intensity adder are achieved. The results of this study indicate that, with a simple process, the TEAI and dual-additives based 2D/3D perovskite photodetectors have promising applications in light-intensity adder and optical communication systems.

Emerging Single-Photon Detectors Based on Low-Dimensional Materials

Single-photon detectors (SPDs) that can sense individual photons are the most sensitive instruments for photodetection. Established SPDs such as conventional silicon or III-V compound semiconductor avalanche diodes and photomultiplier tubes have been used in a wide range of time-correlated photon-counting applications, including quantum information technologies, in vivo biomedical imaging, time-of-flight 3D scanners, and deep-space optical communications. However, further development of these fields requires more sophisticated detectors with high detection efficiency, fast response, and photon-number-resolving ability, etc. Thereby, significant efforts have been made to improve the performance of conventional SPDs and to develop new photon-counting technologies. In this review, the working mechanisms and key performance metrics of conventional SPDs are first summarized. Then emerging photon-counting detectors (in the visible to infrared range) based on 0D quantum dots, 1D quantum nanowires, and 2D layered materials are discussed. These low-dimensional materials exhibit many exotic properties due to the quantum confinement effect. And photodetectors built from these nD-materials (n = 0, 1, 2) can potentially be used for ultra-weak light detection. By reviewing the status and discussing the challenges faced by SPDs, this review aims to provide future perspectives on the research directions of emerging photon-counting technologies.

Transparent graphene electrodes based hybrid perovskites photodetectors with broad spectral response from UV-visible to near-infrared

A new class of transparent graphene electrode based organic-inorganic halide perovskite photodetectors with broad spectral response is developed. These ultrasensitive devices exhibit high ON/OFF current ratio, high linear dynamic range, broad spectral range, excellent detection for weak light and easy fabrication with low-cost. Their semi-transparent feature and distinct photodetecting function for both sides would provide new applications affecting our daily lives.

Low-energy room-temperature optical switching in mixed-dimensionality nanoscale perovskite heterojunctions

Long-lived photon-stimulated conductance changes in solid-state materials can enable optical memory and brain-inspired neuromorphic information processing. It remains challenging to realize optical switching with low-energy consumption, and new mechanisms and design principles giving rise to persistent photoconductivity (PPC) can help overcome an important technological hurdle. Here, we demonstrate versatile heterojunctions between metal-halide perovskite nanocrystals and semiconducting single-walled carbon nanotubes that enable room-temperature, long-lived (thousands of seconds), writable, and erasable PPC. Optical switching and basic neuromorphic functions can be stimulated at low operating voltages with femto- to pico-joule energies per spiking event, and detailed analysis demonstrates that PPC in this nanoscale interface arises from field-assisted control of ion migration within the nanocrystal array. Contactless optical measurements also suggest these systems as potential candidates for photonic synapses that are stimulated and read in the optical domain. The tunability of PPC shown here holds promise for neuromorphic computing and other technologies that use optical memory.

Narrowband Near-Infrared Perovskite/Polymer Hybrid Photodetectors

The distinct visible-blind narrowband near-infrared (NIR) photodetection behaviors in the perovskite/polymer hybrid photodetectors (PDs) have been investigated. The narrowband NIR response in the hybrid PDs is realized through the buildup of the space charges at the perovskite/polymer interface. The semiconducting perovskite layer acts as an internal NIR bandpass due to its high absorption to the visible light and high transparency to the NIR light. It also acts as an excellent hole-transporting layer, facilitating the efficient extraction of the holes generated in the low band gap NIR light-absorbing polymer blend layer. The hybrid PDs thus demonstrated have a -3 dB cutoff frequency of 300 kHz, providing an exciting option for a plethora of applications in bioimaging, environmental detection, and security monitoring.

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.

Role of the Metal-Semiconductor Interface in Halide Perovskite Devices for Radiation Photon Counting

Halide perovskites are promising optoelectronic semiconductors. For applications in solid-state detectors that operate in low photon flux counting mode, blocking interfaces are essential to minimize the dark current noise. Here, we investigate the interface between methylammonium lead tri-iodide (MAPbI₃) single crystals and commonly used high and low work function metals to achieve photon counting capabilities in a solid-state detector. Using scanning photocurrent microscopy, we observe a large Schottky barrier at the MAPbI₃/Pb interface, which efficiently blocks dark current. Moreover, the shape of the photocurrent profile indicates that the MAPbI₃ single-crystal surface has a deep fermi level close to that of Au. Rationalized by first-principle calculations, we attribute this observation to the defects due to excess iodine on the surface underpinning emergence of deep band-edge states. The photocurrent decay profile yields a charge carrier diffusion length of 10-25 μm. Using this knowledge, we demonstrate a single-crystal MAPbI₃ detector that can count single γ-ray photons by producing sharp electrical pulses with a fast rise time of <2 μs. Our study indicates that the interface plays a crucial role in solid-state detectors operating in photon counting mode.

Dual-Phase CsPbCl3-Cs4PbCl6 Perovskite Films for Self-Powered, Visible-Blind UV Photodetectors with Fast Response

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl₃-Cs₄PbCl₆ films. It is achieved by spin-coating of a certain dose of CH₃NH₃Cl/CsCl solution onto a CsI-PbBr₂-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl₃-Cs₄PbCl₆ film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl₃-Cs₄PbCl₆ film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W^-1, an exceptional specific detectivity (D*) maximum of 1.35 × 10¹² Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.