Defect Passivation on Lead-Free CsSnI3 Perovskite Nanowires Enables High-Performance Photodetectors with Ultra-High Stability

Simultaneous Regulation of Crystallization and Suppression of Oxidation in CsSnI3 Perovskite Enables Efficient and Stable Near-Infrared Light-Emitting Diodes

Tin-based halide perovskite light-emitting diodes (PeLEDs) emitting in the near-infrared region beyond 900 nm hold tremendous potential for applications in night vision, biomedicine, and communications. However, rapid crystallization and oxidation of Sn2+ in tin-based perovskites pose significant challenges for achieving stable PeLEDs with high performance. Here, we report an efficient all-inorganic CsSnI3-based PeLED by employing a multifunctional hesperetin additive to modulate the crystallization kinetics and inhibit the oxidation process of the perovskite films. Hesperetin possesses hydroxyl groups alongside oxygen atoms offering lone electron pairs, which form hydrogen bonds with I- and strongly coordinate with Sn2+, respectively, slowing down crystallization of CsSnI3 and resulting in high coverage density films. Importantly, the coordination of hesperetin with Sn2+ protects the perovskite films from Sn2+-to-Sn4+ oxidation. Finally, we demonstrate efficient and stable PeLEDs with a peak at 948 nm, an external quantum efficiency of 4.7%, and a half-lifetime of over 11 h.

Optimizing Lasing Performance of CsPbBr3 Microplates by Regulating Exciton Recombination Dynamics with Pressure

This study aims to achieve an ultralow lasing threshold in CsPbBr3 microplates (MPs), a crucial step toward developing electrically driven micro/nanolasers for optics integrated chips. We investigate the lasing behavior of CsPbBr3 MPs under varying pressures by using static-state photoluminescence (PL), time-resolved PL (TRPL), and first-principles theory calculations based on density functional theory (DFT). Our results reveal that the lasing threshold initially decreases and then increases, with a critical turning point at 0.44 GPa. Notably, we achieve an optimal lasing threshold of 20.87 μJ/cm2 after releasing pressure from 1.87 GPa, highlighting the potential of pressure modulation to optimize the lasing performance. At low pressure, pressure-induced phonon hardening enhances the barrier, preventing excitons decay from free states to trapping states. Conversely, at higher pressure, the increased density of surface defects, due to pressure-induced anisotropic contraction of lattice constants along the c-axis, leads to excitons decay from free states to trapping states. For CsPbBr3 MPs, it is evident that only free excitons contribute to lasing, while both free and trapped excitons contribute to luminescence. These findings offer a novel strategy to optimize the lasing performance of perovskite micro/nanolasers, significantly advancing their potential for practical applications in optoelectronic devices.

First-principles study of the surface energies and electronic structures of γ-CsSnI3 surfaces

All-inorganic perovskite CsSnI3 has attracted intense research interests due to its prominent optoelectronic properties, high thermal stability, and environmentally friendly character. The surface energies and electronic structures of black orthorhombic (γ) CsSnI3 surfaces are investigated by using first-principles methods. The anisotropic and termination-dependent surface energies of low-index surfaces (i.e., the (110), (001), (100) and (101) surfaces) are obtained, providing important data for CsSnI3, since these values are difficult to be measured in experiments. The CsI-terminated (110) and (001) surfaces are predicted to be the most stable and their surface energies are close, making the cube-shape of nanocrystals favorable at thermodynamic equilibrium, which is consistent with the experimental observations. Calculated surface electronic structures show that the quantum confinement effect is orientation dependent. The band gaps of the (100) and (101) surfaces are significantly larger than those of the (110) and (001) surfaces by using slabs with similar thickness. This distinction can be attributed to different 'electronic dimensionalities' of these surfaces. Our results provide physical insights into the thermodynamic stability and electronic properties of CsSnI3 surfaces.

Exploring Nanoscale Perovskite Materials for Next-Generation Photodetectors: A Comprehensive Review and Future Directions

The rapid advancement of nanotechnology has sparked much interest in applying nanoscale perovskite materials for photodetection applications. These materials are promising candidates for next-generation photodetectors (PDs) due to their unique optoelectronic properties and flexible synthesis routes. This review explores the approaches used in the development and use of optoelectronic devices made of different nanoscale perovskite architectures, including quantum dots, nanosheets, nanorods, nanowires, and nanocrystals. Through a thorough analysis of recent literature, the review also addresses common issues like the mechanisms underlying the degradation of perovskite PDs and offers perspectives on potential solutions to improve stability and scalability that impede widespread implementation. In addition, it highlights that photodetection encompasses the detection of light fields in dimensions other than light intensity and suggests potential avenues for future research to overcome these obstacles and fully realize the potential of nanoscale perovskite materials in state-of-the-art photodetection systems. This review provides a comprehensive overview of nanoscale perovskite PDs and guides future research efforts towards improved performance and wider applicability, making it a valuable resource for researchers.

Enhanced amplified spontaneous emission performance through effective regulation of phase distribution in Ruddlesden-Popper perovskite films

Ruddlesden-Popper (RP) perovskites promise next-generation gain media for laser devices. However, most RP perovskite lasers are still suffering from inferior performance characteristics, such as inadequate energy transfer, unstable emission, and short lifetime. To address the above problems, high crystalline quality, compact, and smooth PEA2FA2Pb3Br10 films with uniform phase distribution were successfully prepared by ionic liquid (IL) methylammonium acetate (MAAc) in an air environment. Compared with the PEA2FA2Pb3Br10 film prepared by the traditional solvent dimethyl sulfoxide (DMSO), an enhanced amplified spontaneous emission (ASE) with a lower threshold of 58 µJ·cm-2 from the MAAc-treated film was obtained under nanosecond laser excitation. The transient absorption (TA) spectroscopy revealed that a uniform phase distribution and more efficient energy transfer processes were achieved in the PEA2FA2Pb3Br10-MAAc film, leading to an enhanced band-to-band spontaneous emission process. Furthermore, the films exhibited better stability, showing no signs of degradation under the 120 min pulsed laser pumping in air and stability of ASE spectra at even 95% humidity conditions. This study provides an important foundation for achieving high-performance optically pumped lasers based on the unique RP perovskites.

Metal-Organic Framework-Based Photodetectors

The unique and interesting physical and chemical properties of metal-organic framework (MOF) materials have recently attracted extensive attention in a new generation of photoelectric applications. In this review, we summarized and discussed the research progress on MOF-based photodetectors. The methods of preparing MOF-based photodetectors and various types of MOF single crystals and thin film as well as MOF composites are introduced in details. Additionally, the photodetectors applications for X-ray, ultraviolet and infrared light, biological detectors, and circularly polarized light photodetectors are discussed. Furthermore, summaries and challenges are provided for this important research field.

Synchronous Regulation Strategy of Pyrrolidinium Thiocyanate Enables Efficient Perovskite Solar Cells and Self-Powered Photodetectors

Developing inventive approaches to control crystallization and suppress trap defects in perovskite films is crucial for achieving efficient perovskite photovoltaics. Here, a synchronous regulation strategy is developed that involves the infusion of a zwitterionic ionic liquid additive, pyrrolidinium thiocyanate (PySCN), into the perovskite precursor to optimize the subsequent crystallization and defects. PySCN modification not only orchestrates the crystallization process but also deftly addresses trap defects in perovskite films. Within this, SCN- compensates for positively charged defects, while Py+ plays the role of passivating negatively charged defects. Based on the vacuum flash evaporation without anti-solvent, the air-processed perovskite solar cells (PSCs) with PySCN modification can achieve an extraordinary champion efficiency of 22.46% (0.1 cm2) and 21.15% (1.0 cm2) with exceptional stability surpassing 1200 h. Further, the self-powered photodetector goes above and beyond, showcasing an ultra-low dark current of 2.13 × 10-10 A·cm-2, a specific detection rate of 6.12 × 1013 Jones, and an expansive linear dynamic range reaching an astonishing 122.49 dB. PySCN modification not only signifies high efficiency but also ushers in a new era for crystallization regulation, promising a transformative impact on the optoelectronic performance of perovskite-based devices.

Self-Powered MAPbI3 Heterojunction Photodetector with Gradient-Level Electron Transport Layers and Dual Pyro-Phototronic Effects

An electron transport layer (ETL) with a suitable gradient energy level can enhance electron transfer, suppress carrier recombination, and effectively improve the photoresponse of photodetectors (PDs). In this letter, a series of ITO/ZnO/CdS/MAPbI3/Spiro-OMeTAD heterojunction PDs were prepared by incorporating a ZnO layer at the CdS/ITO interface upon varying the thickness from 0 to 95 nm. The optimized band arrangement in the PD results in an excellent self-powering ability and improved photoresponse. Moreover, both the photovoltaic and pyroelectric responses strongly correlate with the thickness of the ZnO layer. The PD with an optimal ZnO thin film thickness of 50 nm achieves a huge responsivity (R) of 1.19 × 104 V/W and detectivity (D) of 2.22 × 109 Jones, primarily due to the strengthened pyro-phototronic effects enabled by the dual ETL layers. In addition, the enhanced pyroelectric effect broadens the spectral range of the PD to 360-1550 nm, largely surpassing the band gap of the heterojunction.

Recent Progress of Low-Toxicity Poor-Lead All-Inorganic Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have achieved an impressive certified efficiency of 25.7%, which is comparatively higher than that of commercial silicon solar cells (23.3%), showing great potential toward commercialization. However, the low stability and high toxicity due to the presence of volatile organic components and toxic metal lead in the perovskites pose significant challenges. To obtain robust and low-toxicity PSCs, substituting organic cations with pure inorganic cations, and partially or fully replacing the toxic Pb with environmentally benign metals, is one of the promising methods. To date, continuous efforts have been made toward the construction of highly performed low-toxicity inorganic PSCs with astonishing breakthroughs. This review article provides an overview of recent progress in inorganic PSCs in terms of lead-reduced and lead-free compositions. The physical properties of poor-lead all-inorganic perovskites are discussed to unveil the major challenges in this field. Then, it reports notable achievements for the experimental studies to date to figure out feasible methods for efficient and stable poor-lead all-inorganic PSCs. Finally, a discussion of the challenges and prospects for poor-lead all-inorganic PSCs in the future is presented.

Decade Milestone Advancement of Defect-Engineered g-C3N4 for Solar Catalytic Applications

Over the past decade, graphitic carbon nitride (g-C3N4) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C3N4 is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the "all-in-one" defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultra-active coordinated environment (M-Nx, M-C2N2, M-O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra (fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C3N4 "customization", motivating more profound thinking and flourishing research outputs on g-C3N4-based photocatalysis.

Waterproof and Flexible Perovskite Photodetector Enabled By P-type Organic Molecular Rubrene with High Moisture and Mechanical Stability

Metal halide perovskite films have gained significant attention because of their remarkable optoelectronic performances. However, their poor stability upon the severe environment appears to be one of the main facets that impedes their further commercial applications. Herein, a method to improve the stability of flexible photodetectors under water and humidity environment without encapsulation is reported. The devices are fabricated using the physical vapor deposition method (Pulse Laser Deposition & Thermal Evaporation) under high-vacuum conditions. An amorphous organic Rubrene film with low molecular polarity and high elastic modulus serves as both a protective layer and hole transport layer. After immersed in water for 6000 min, the photoluminescence intensity attenuation of films only decreased by a maximum of 10%. The demonstrator device, based on Rubrene/CsPbBr3 /ZnO heterojunction confirms that the strategy not only enhances device moisture and mechanical stability but also achieves high sensitivity in optoelectronic detection. In self-powered mode, it has a fast response time of 79.4 µs /207.6 µs and a responsivity 124 mA W-1 . Additionally, the absence of encapsulation simplifies the fabrication of complex electrodes, making it suitable for various applications. This study highlights the potential use of amorphous organic films in improving the stability of perovskite-based flexible devices.

Perovskite-based photodetector for real-time and quantitative monitoring of sports motion

Reliable monitoring the movement amplitude and dynamics during sports exercise is significant for improving training results and preventing training wound. Here, we present a printed perovskite-based photodetector for real-time and quantitative monitoring of sports motion. The ordered nucleation and growth of perovskite crystals are regulated by the 4-acetamidothiophenol (AMTP) at the interface, which promotes the size of perovskite crystals into the micrometer. Benefiting from the uniformity of the AMTP-regulated MAPbI3, the as-prepared photodetector gives great photocurrent response under indoor light or outdoor light. During the exercise, real-time monitoring sports motion is achieved through detecting the illumination changing of photodetectors attaching on the wrist and ankles. Moreover, twelve kinds of common sports can be quantitatively analyzed with the detection of illumination changing on the photodetector. Such photodetector provides an efficient measurement method of wearable electronics for sports monitoring.

Two-step spin coating CsPbBr3 thin films and photodetectors in the atmosphere

Recently, inorganic halide perovskites, especially CsPbBr₃, have been attracting attention because of their high efficiency, wide color gamut, and narrow luminescent spectrum. To elevate the perovskite devices' performance, optimizations of crystalline quality, device structures, and fabrication process are essential. Currently, the state-of-the-art fabrication approach of CsPbBr₃ is spin-coating in an inert environment (nitrogen, argon, etc.), which requires temperature and humidity control. In this work, a CsPbBr₃-based visible photodetector (PD) is realized in a humid atmosphere, whose performances were comparable to those reported in an inert glovebox. The dependencies of responsivity and transient time on CsBr coating layer numbers and electrode period were also investigated. The best device performance was obtained with 4 layers of CsBr coating with a responsivity of 107.2 mA/W, detectivity of 4.29 × 10¹⁰ Jones, and quantum efficiency of 25.4%. The rise time of the 3-4-layer CsBr-coated PD was reduced by the higher crystalline quality and carrier mobility, while the decay time of the 1-layer CsBr-coated PD was faster since the dense defect induced non-radiative recombination centers. With the period T increasing, the responsivity decreased, while the transient times increased. We believe that our results could benefit the future optimization of perovskite materials and PDs.

Graphene oxide:Fe2O3 nanocomposites for photodetector applications: experimental and ab initio density functional theory study

In this report, a GO:Fe2O3 nanocomposite was synthesized using a one-step covalent attachment approach using a sol-gel technique. The optical absorbance, photoconductive, photo-capacitive, and electrical properties were obtained using spectroscopy, and current-voltage (I-V) measurements. An enhanced optical absorbance with corresponding band gap reduction is observed when Fe2O3 nanoparticles are incorporated in GO. A corresponding enhanced photoconductance in the order of ×101 was observed due to the impact of band gap narrowing. The enhanced photoconductivity and photo-capacitance can be attributed to energy and charge transfer between GO and Fe atoms, leading to the generation of photo-induced excitons. Density function theory calculations indicate increased charge transfer when GO is doped with Fe-O atoms, which is consistent with experimental data. The observed results could potentially enable the use of GO:Fe2O3 nanocomposites for photodetectors and other optoelectronic applications.

Perovskite-like Silver Halide Single-Crystal Microbelt Enables Ultrasensitive Flexible X-ray Detectors

Lead halide perovskite single crystals have attracted wide interest in the field of X-ray detection due to their excellent photophysical properties. However, their inherent toxicity and high thickness restrict their applications in flexible devices. In this paper, designing a micronanometer-scale X-ray detector based on all-inorganic lead-free CsAg2I3 (CAI) single crystal microbelts (MBs) has addressed the above issues. These CAI single crystal MBs can be synthesized on various substrates with high crystal quality and excellent stability. Based on their excellent characteristics of the CAI MBs, we fabricate single CAI MB devices with an Au/CAI/Au structure, which shows not only good ultraviolet photoresponse characteristics, but also excellent X-ray detection performance. The optimized CAI photodetectors exhibit a responsivity of 23.59 mA/W, a high detectivity of 1010 Jones, and a fast response speed. For X-ray detection performance, a sensitivity of up to 515.49 μC Gyair-1 cm-2 and a detection limit of as low as 14.65 μGyair s-1 are achieved with outstanding operation stability and excellent long-term stability. Furthermore, our devices also showed excellent applicability for X-ray imaging, which is promising for their use in X-ray detection and imaging. Finally, flexible X-ray detectors are fabricated by using thin CAI single-crystal MBs and demonstrate good flexibility under different bending radii and bending cycles. Our work shows the potential for developing highly sensitive flexible integrated micro/nano optoelectronic devices by using lead-free perovskite analogue single crystals.