Highly Sensitive Tin-Lead Perovskite Photodetectors with Over 450 Days Stability Enabled by Synergistic Engineering for Pulse Oximetry System

Water-stable perovskite/metallic nanocomposites-based SERS aptasensor for detection of neuron-specific enolase

Perovskite/metallic heterojunction-based surface enhanced Raman scattering (SERS) substrates have been proven to be capable of providing Raman enhancement. However, the inherent water instability and poor dispersibility of perovskite/metallic nanocomposites-based SERS substrates pose significant challenges to their application in aqueous environments. Herein, polydopamine (PDA)-encapsulated cesium lead bromide (CsPbBr3) adsorbing gold nanoparticles (AuNPs), termed as CsPbBr3@PDA@AuNPs, is prepared as SERS substrate, which exhibits excellent water stability and SERS activity. Dopamine as organic ligand not only passivates surface defects during the growth of perovskite nanocrystals, but also forms porous PDA protective layer, effectively preventing degradation of perovskite in aqueous medium. Meanwhile, PDA with abundant functional groups and conjugated π structure will adsorb AuNPs and promote electron flow between CsPbBr3 and AuNPs, resulting in strong SERS activity. Based on the results, a SERS aptasensor has been fabricated by conjugation between CsPbBr3@PDA@AuNPs and double-stranded DNA (dsDNA), which is composed of neuron-specific enolase (NSE) aptamer and partial complementary signal-stranded DNA (ssDNA). The working strategy of as-fabricated SERS aptasensor is based on the conformational change (of ssDNA)-triggered Raman response for the detection of NSE. Upon the addition of NSE, the specific binding of NSE aptamers to NSE can convert rigid dsDNA into a flexible ssDNA, and the Cy5 signal molecule modified at the end of ssDNA will close to CsPbBr3@PDA@AuNPs SERS substrate, generating significant Raman signals with the lower limit of detection (1.02 pg/mL) of NSE. The SERS aptasensor has broad application prospect in the field of life/medicine science fields (e.g. early diagnosis and screening of disease).

Electrochemical Doping of Halide Perovskites with Silver Interstitial Ions: Mechanistic Insights and Enhanced Performance in Memristor Applications

Halide perovskites have garnered significant attention for their exceptional carrier mobility, balanced bipolar transport properties, and ion-electron mixing conductivity, making them highly promising for applications, such as solar cells, photodetectors, and memristors. Despite their potential, intrinsic ions and defects within these materials complicate effective doping, and interactions between metal electrodes and perovskite materials can trigger interfacial chemical reactions that compromise device stability and performance. This study examines the influence of Ag electrodes on perovskite devices, specifically investigating the n-doping effects of Agi+ interstitial ions in MAPbI3 perovskites through an integrated approach combining first-principles density functional theory (DFT) calculations and experimental analysis. Findings reveal that Agi+ interstitial ions, generated electrochemically at Ag electrodes, penetrate the MAPbI3 structure and migrate under an applied electric field, achieving stable n-doping under controlled bias conditions. Detailed characterization of the doping process was conducted using current density-time (J-t) measurements, electrochemical AC impedance (EIS), TOF-SIMS/XPS depth profiling, and temperature/illumination-dependent studies. Additionally, the memristive behavior of the device, including doping mechanisms and the formation of metallic conductive filaments, was demonstrated, offering insights into its potential applications in advanced electronics. These findings elucidate the physicochemical interactions at metal-perovskite interfaces under bias in diode devices.

Fully degradable, transparent, and flexible photodetectors using ZnO nanowires and PEDOT:PSS based nanofibres

Transparent light detection devices are attractive for emerging see-through applications such as augmented reality, smart windows and optical communications using light fidelity (Li-Fi). Herein, we present flexible and transparent photodetectors (PDs) using conductive poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS): Ag nanowires (NWs) based nanofibres and zinc oxide (ZnO) NWs on a transparent and degradable cellulose acetate (CA) substrate. The electrospun (PEDOT:PSS): Ag NW-based nanofibres exhibit a sheet resistance of 11 Ω/sq and optical transmittance of 79% (at 550 nm of wavelength). The PDs comprise of ZnO NWs, as photosensitive materials, bridging the electrode based on conductive nanofibres on CA substrate. The developed PDs exhibit high responsivity (1.10 ×106 A/W) and show excellent stability under dynamic exposure to ultraviolet (UV) light, and on both flat and curved surfaces. The eco-friendly PDs present here can degrade naturally at the end of life - thus offering an electronic waste-free solution for transparent electrodes and flexible optoelectronics applications.

Three Birds with One Stone: Triple Defect Passivation of Tris(2,2,2-trifluoroethyl) Phosphate Enables 25.69% Efficient Inverted Perovskite Solar Cells

Defect passivation is widely acknowledged as a crucial strategy for enhancing the efficiency and stability of perovskite solar cells (PSCs). However, it remains a formidable challenge to effectively address multiple defects simultaneously on both the top and bottom surfaces of perovskite films, as well as within the bulk, through a facile method. To tackle this dilemma, we have devised a triple passivation strategy, aiming to achieve a holistic passivation of defects at the aforementioned locations using a singular passivator. Specifically, a multifunctional molecule, tris(2,2,2-trifluoroethyl) phosphate (TTFP), is meticulously engineered as an additive in the antisolvent. This approach capitalizes a top-down gradient distribution of TTFP along the perovskite film, thereby enabling to mitigate the interfacial and bulk defects. Meanwhile, the unique molecular structure of TTFP facilitates simultaneous interactions with both cationic and anionic defects. Additionally, TTFP exerts a pronounced influence on the crystallization kinetics, thereby promoting the formation of highly crystalline perovskite films with substantially enlarged grain sizes. Consequently, the TTFP-based devices exhibit a champion power conversion efficiency (PCE) of 25.69%, accompanied by a notable improvement in stability. This work represents the successful implementation of comprehensive defect passivation, marking a significant instance in the advancement of efficient and stable PSCs technology.

Deep-Learning-Based Analysis of Electronic Skin Sensing Data

E-skin is an integrated electronic system that can mimic the perceptual ability of human skin. Traditional analysis methods struggle to handle complex e-skin data, which include time series and multiple patterns, especially when dealing with intricate signals and real-time responses. Recently, deep learning techniques, such as the convolutional neural network, recurrent neural network, and transformer methods, provide effective solutions that can automatically extract data features and recognize patterns, significantly improving the analysis of e-skin data. Deep learning is not only capable of handling multimodal data but can also provide real-time response and personalized predictions in dynamic environments. Nevertheless, problems such as insufficient data annotation and high demand for computational resources still limit the application of e-skin. Optimizing deep learning algorithms, improving computational efficiency, and exploring hardware-algorithm co-designing will be the key to future development. This review aims to present the deep learning techniques applied in e-skin and provide inspiration for subsequent researchers. We first summarize the sources and characteristics of e-skin data and review the deep learning models applicable to e-skin data and their applications in data analysis. Additionally, we discuss the use of deep learning in e-skin, particularly in health monitoring and human-machine interactions, and we explore the current challenges and future development directions.

Enhancing the Performance of Perovskite Environmental Sensors through the Synergistic Effect of the Natural Antioxidant

All-inorganic perovskite CsPbX3 is considered to be the next-generation optical material due to its excellent optical properties and potential applications in optoelectronics. However, the inherent ionic crystal property makes it susceptible to interaction with moisture and oxygen in the ambient atmosphere and hinders the development of stable perovskite devices. Herein, a natural and nontoxic molecule, ascorbic acid (AA), is introduced to improve the performance of perovskite nanocrystals. Experimental results reveal that the strong coordination between carbonyl groups and undercoordinated Pb2+, together with the hydrogen bonding interaction between hydroxyl groups and defects of halide ions in AA, suppress nonradiative recombination. In addition, with the synergistic effect of the C═O and -OH groups in AA, the perovskite crystal structure exhibits excellent stability due to hydrogen bonding. Finally, the demonstration of humidity sensing based on perovskites has been presented. It is shown that the humidity sensor exhibits good sensitivity in the range of 30%-80% relative humidity, with a detection limit of 3.9% and a response time of 46 s. This work provides a low-cost, nontoxic, and efficient modification approach and demonstrates an easy way to improve the performance and humidity stability of perovskite.

Quasi-Single-Crystal Tin Halide Perovskite Films with High Structural Integrity for Near-Infrared Imaging Array Enabling Hidden Object Recognition

Near-infrared (NIR) image sensors based on solution-processed thin film are gaining prominence in various applications, including security detection, remote sensing, medical imaging, and environmental monitoring, owing to superior penetration capabilities of NIR light. However, the reported perovskite image sensors suffer from limited resolution and performance due to poor structural integrity, bioincompatibility, and constrained response wavelength range from lead-based perovskite materials employed. In this study, we present non-toxic quasi-single-crystal (QSC) CH(NH2)2SnI3 (FASnI3) perovskite films, prepared via a simple spin-coating technique, that demonstrate high structural integrity and effective NIR response. Through a series of in situ characterizations, we reveal that the orderly growth mode of QSC-FASnI3 perovskite films enables a more oriented crystal growth with reduced trap and grain boundaries. Consequently, self-powered NIR photodetector based on QSC-FASnI3 films exhibited large detectivity over 1013 Jones in the NIR range (780-890 nm). Ultimately, due to the high structural integrity, the high-resolution 64×64 (4096) pixels NIR imaging array, exhibiting reduced photo and dark response non-uniformity value, was fabricated on the thin-film transistors (TFT) backplanes, enabling ultraweak NIR light (63 nW cm-2) real-time imaging, fingerprint imaging, and hidden object recognition. This work pioneers the application of lead-free perovskite for high-resolution NIR imaging arrays.

Capillary condensation-driven growth of perovskite nanowire arrays for multi-functional photodetector

Metal-halide perovskite nanowire array photodetectors based on the solution method are valuable in the field of polarized light detection because of their unique one-dimensional array structure and excellent photoelectric performance. However, the limited wettability of liquids poses challenges for achieving large-scale and high-quality perovskite nanowire arrays. To address this issue, we develop a facile method utilizing capillary condensation to grow high-quality centimeter-scale perovskite nanowire arrays. Based on these nanowires, the fabricated photodetector showcases specific detectivities of 1.95 × 1013 jones, surpassing commercially available silicon detectors in weak-light detection capabilities. The weak-light imaging capability of our nanowire photodetectors has been successfully demonstrated at intensities below 54 nW/cm2. Moreover, the nanowire arrays also display excellent polarization absorption characteristics, promising applications in polarized light detection. Notably, the perovskite nanowire arrays can be grown on flexible substrates by employing capillary condensation, which retains 83% of their properties after 2000 bending cycles. This research enhances the potential of perovskite nanowire arrays photodetector in practical applications.

Terminal Fluorination Modulates Crystallinity and Aggregation of Fully Non-Fused Ring Electron Acceptors for High-Performance and Durable Near-Infrared Organic Photodetectors

High dark current density (Jd) severely hinders further advancement of near-infrared organic photodetectors (NIR OPDs). Herein, we tackle this grand challenge by regulating molecular crystallinity and aggregation of fully non-fused ring electron acceptors (FNREAs). TBT-V-F, which features fluorinated terminals, notably demonstrates crystalline intensification and a higher prevalence predominance of J-aggregation compared to its chlorinated counterpart (TBT-V-Cl). The amalgamation of advantages confers TBT-V-F-based OPDs with lower nonradiative energy loss, improved charge transport, decreased energetic disorder, and reduced trap density. Consequently, the corresponding self-powered OPDs exhibit a 40-fold decrease in Jd, a remarkable increase in detectivity (D*sh), faster response time, and superior thermal stability compared to TBT-V-Cl-based OPDs. Further interfacial optimization results in an ultra-low Jd of 7.30×10-12 A cm-2 with D*sh over 1013 Jones in 320-920 nm wavelength and a climax of 2.2×1014 Jones at 800 nm for the TBT-V-F-based OPDs, representing one of the best results reported to date. This work paves a compelling material-based strategy to suppress Jd for highly sensitive NIR OPDs, while also illustrates the viability of FNREAs in construction of stable and affordable NIR OPDs for real-world applications.

High Performance Perovskite Photodiodes via Molecule-Assisted Interfacial and Bulk Modulations

Metal halide perovskites have attracted significant attention in photodetection due to their superior photophysical properties and improved stability. However, the performance of their photodiodes is predominantly limited by non-radiative recombination within the perovskite layer or at interfaces. Here, molecular engineering via phenylethylammonium chloride for interfacial modulation and methylenediammonium dichloride for bulk modulation is introduced into vertical perovskite photodiodes to boost the photodetection performance. The responsivity at 635 nm excitation increased from 0.09 to 0.33 A W-1 with interfacial modulation, compared to the original perovskite device, and is further improved to 0.40 A W-1 with the combined effects of interfacial and bulk modulations (i.e., synergistic bimolecular engineering). The optimized photodiodes demonstrated high detectivity of over 1011 Jones, a rapid response time of ≈1 µs, and a linear dynamic range of ≈100 dB. Furthermore, the photocurrent exhibited a U-shaped dependence on temperature ranging from 10 to 300 K, with linearity breaking under strong illumination at low temperatures. These results confirmed that molecular engineering is the promising strategy for achieving high-performance perovskite photodetectors.

Highly Sensitive Perovskite Photoplethysmography Sensor for Blood Glucose Sensing Using Machine Learning Techniques

Accurate non-invasive monitoring of blood glucose (BG) is a challenging issue in the therapy of diabetes. Here near-infrared (NIR) photoplethysmography (PPG) sensor based on a vapor-deposited mixed tin-lead hybrid perovskite photodetector is developed. The device shows a high detectivity of 5.32 × 1012 Jones and a large linear dynamic range (LDR) of 204 dB under NIR light, guaranteeing accurate extraction of eleven features from the PPG signal. By a combination of machine learning, accurate prediction of blood glucose level with mean absolute relative difference (MARD) as small as 2.48% is realized. The self-powered PPG sensor also works for real-time outdoor healthcare monitors using sunlight as a light source. The potential for early diabetes diagnoses by the perovskite PPG sensor is demonstrated.

Ultrafast Response and Broad Detection Range of a Ternary Cation Perovskite Single-Crystal Thin Film Photodetector for Imaging

FA-MA-Cs ternary cation perovskite exhibits excellent optoelectronic properties and high stabilities against humidity and light soaking and thus has aroused extensive attention in polycrystalline thin film solar cells. Compared with polycrystalline counterparts, FA-MA-Cs ternary cation perovskite single-crystal thin films (SCTFs) have lower defects, better carrier transport capacity, and stability because of lacking grain boundary defects. However, the immature growth technology of SCTFs restricts digging out its optoelectronic potential. Here, we proposed an improved space-confined method to grow large area FA0.9 MA0.05Cs0.05PbI2.7Br0.3 SCTFs using a tunable heating area to control the nucleation and growth process. Its area reaches 64 mm2 with a thickness of 26 μm. The SCTF exhibits high crystallinity, low defect density, long carrier lifetime, and high moisture resistance stability. Besides, a photosensitive chip based on a planar metal-semiconductor-metal photodetector demonstrates linear response to the three primary colors, with a photosensitive range that is 1.5 times that of protocol 3 wide color gamut. Under high-frequency light sources, the on/off ratio reaches 3.9 × 103, and the response time can be as low as 400 ns. Such ultrafast response speed and broad photosensitive range are successfully achieved for imaging applications.

Nanofiber Space-Confined Fabrication of High-Performance Perovskite Films for Flexible Conversion of Fluorescence Quantum Yields in LED Applications

Perovskite is an advanced optoelectronic semiconductor material that has garnered significant attention in recent years. However, its drawback lies in its environmental instability, limiting its practical applications. To tackle this issue, this research delved into the idea of creating a space-confined structure and used electrospinning to produce a film of perovskite nanocomposite fibers. By effectively encapsulating perovskite nanocrystals into a polymer matrix, the perovskite could be shielded from water and oxygen in the environment, thereby reducing the likelihood of perovskite decomposition and enhancing the stability of its structure and properties. This study examined the influence of material composition and the spinning process on the nanofiber structure to create good spatial confinement. This strategy resulted in a high photoluminescence quantum yield of over 80% and a long-term environmental stability of as long as 1000 h over 90% of the original PLQY. By harnessing the flexibility of the composite fibers, this study demonstrated the potential applications and performance of this nanocomposite film in flexible quantum fluorescence conversion for LED applications.

Triiodide Formation Governs Oxidation Mechanism of Tin-Lead Perovskite Solar Cells via A-Site Choice

Mixed tin-lead (Sn-Pb) halide perovskites stand out as promising materials for next-generation photovoltaics and near-infrared optoelectronics. However, their sensitivity to oxidative degradation remains a major hurdle toward their widespread deployment. A holistic understanding of their oxidation processes considering all their constituent ions is therefore essential to stabilize these materials. Herein, we reveal that A-site cation choice plays an inconspicuous yet crucial role in determining Sn-Pb perovskite stability toward oxidation. Comparing typical A-site compositions, we show that thin films and solar cells containing cesium are more resistant to oxidative stress relative to their methylammonium analogs. We identify degradation in these compositions to be closely linked to the presence of triiodide, a harmful species evolving from native I2 oxidants. We find that hydrogen bonding between methylammonium and I2 promotes triiodide formation, while the strong polarizing character of cesium limits this process by capturing I2. Inspired from these findings, we design two strategies to boost stability of sensitive methylammonium-based Sn-Pb perovskite films and devices against oxidation. Specifically, we modulate the polarizing character of surface A-sites in perovskite via CsI and RbI coatings, and we incorporate Na2S2O3 as an I2 scavenging additive. These crucial mechanistic insights will pave the way for the design of highly efficient and stable Sn-Pb perovskite optoelectronics.

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.

Cyano-Coordinated Tin Halide Perovskites for Wearable Health Monitoring and Weak Light Imaging

Low-toxicity tin halide perovskites with excellent optoelectronic properties are promising candidates for photodetection. However, tin halide perovskite photodetectors have suffered from high dark current owing to uncontrollable Sn2+ oxidation. Here, 2-cyanoethan-1-aminium iodide (CNI) is introduced in CH(NH2)2SnI3 (FASnI3) perovskite films to inhibit Sn2+ oxidation by the strong coordination interaction between the cyano group (C≡N) and Sn2+. Consequently, FASnI3-CNI films exhibit reduced nonradiative recombination and lower trap density. The self-powered photodetector based on FASnI3-CNI exhibits low dark current (1.04 × 10-9 A cm-2), high detectivity (2.2 × 1013 Jones at 785 nm), fast response speed (2.62 µs), and good stability. Mechanism studies show the increase in the activation energy required for thermal emission and generated carriers, leading to a lower dark current in the FASnI3-CNI photodetector. In addition, flexible photodetectors based on FASnI3-CNI, exhibiting high detectivity and fast response speed, are employed in wearable electronics to monitor the human heart rate under weak light and zero bias conditions. Finally, the FASnI3-CNI perovskite photodetectors are integrated with a 32 × 32 thin-film transistor backplane, capable of ultraweak light (170 nW cm-2) real-time imaging with high contrast, and zero power consumption, demonstrating the great potential for image sensor applications.

Performance Enhancement of Tin-Based Perovskite Photodetectors through Bifunctional Cesium Fluoride Engineering

Tin halide perovskites are rising as promising candidates for next-generation optoelectronic materials due to their good optoelectronic properties and relatively low toxicity. However, the high defect density and the easy oxidation of Sn2+ have limited their optoelectronic performance. Herein, we report the treatment of the FASnI3 (formamidinium tin, FA) perovskite film by a bifunctional cesium fluoride (CsF) additive, which improves the film quality and significantly enhances the photoelectric performance. The responsivity of the perovskite-based photodetector (PD) with an optimal CsF concentration of 15% is over 60 times larger than that of the PD without CsF. It indicates that both the Cs substitution and the fluoride anion additive from CsF inhibit the oxidation of Sn2+, optimize the crystal growth, and passivate the defects, demonstrating the dual roles of the CsF additive in improving the photoelectric performance. This work offers valuable insights into the additive selection for developing high-quality tin-based perovskite films and devices.

Compact angle-resolved metasurface spectrometer

Light scattered or radiated from a material carries valuable information on the said material. Such information can be uncovered by measuring the light field at different angles and frequencies. However, this technique typically requires a large optical apparatus, hampering the widespread use of angle-resolved spectroscopy beyond the lab. Here we demonstrate compact angle-resolved spectral imaging by combining a tunable metasurface-based spectrometer array and a metalens. With this approach, even with a miniaturized spectrometer footprint of only 4 × 4 μm2, we demonstrate a wavelength accuracy of 0.17 nm, spectral resolution of 0.4 nm and a linear dynamic range of 149 dB. Moreover, our spectrometer has a detection limit of 1.2 fJ, and can be patterned to an array for spectral imaging. Placing such a spectrometer array directly at the back focal plane of a metalens, we achieve an angular resolution of 4.88 × 10-3 rad. Our angle-resolved spectrometers empowered by metalenses can be employed towards enhancing advanced optical imaging and spectral analysis applications.

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.

Polarization-Sensitive Detector Based on MoTe2/WTe2 Heterojunction for Broadband Optoelectronic Imaging

Polarization-sensitive detectors have significant applications in modern communication and information processing. In this study. We present a polarization-sensitive detector based on a MoTe2/WTe2 heterojunction, where WTe2 forms a favorable bandgap structure with MoTe2 after forming the heterojunction. This enhances the carrier separation efficiency and photoelectric response. We successfully achieved wide spectral detection ranging from visible to near-infrared light. Specifically, under zero bias, our photodetector exhibits a responsivity (R) of 0.6 A/W and a detectivity (D*) of 3.6 × 1013 Jones for 635 nm laser illumination. Moreover, the photoswitching ratio can approach approximately 6.3 × 105. Importantly, the polarization sensitivity can reach 3.5 (5.2) at 635 (1310) nm polarized light at zero bias. This study both unveils potential for utilizing MoTe2/WTe2 heterojunctions as polarization-sensitive detectors and provides novel insights for developing high-performance optoelectronic devices.

Metal-Free Perovskites for X-Ray Detection

Metal-free perovskites are a promising class of materials for X-ray detection due to their unique structural, optical, and electrical properties. Here, we first delve into the stoichiometry and geometric argument of metal-free perovskites. Followed, the alternative A/B/X ions and hydrogen-bonding are clearly introduced to further optimize the materials' stability and properties. Finally, we provide a comprehensive overview of their potential applications for flexible X-ray images and prospects for metal-free perovskite development. In conclusion, metal-free perovskite is a promising material for X-ray detection. Its stoichiometric and geometric parameters, ion, and hydrogen bond selection, and application prospects are worthy of further study.

Synergistic Surface Defect Passivation of Ionic Liquids for Efficient and Stable MAPbI3-Based Inverted Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells are fabricated using polycrystalline perovskite thin films, which possess high densities of point and surface defects. The surface defects of perovskite thin films are the key factors that affect the device performance. Therefore, the reduction of harmful defects is the primary task for improving device performance. Therefore, in this study, high-quality perovskite thin films are prepared using an ionic liquid, dithiocarbamate diethylamine (DADA), to passivate the interface. The electron-rich sulfur atom in the DADA molecule chelates with the uncoordinated lead ion in the perovskite films, and the diethylammonium cation forms a hydrogen bond with the free iodine ion, which further improves the passivation. The synergistic passivation and improved morphology of the perovskite thin films substantially reduce the number of charged defects on the film surface and prolong the carrier lifetime. In addition, the DADA surface treatment increases the work function of the perovskite film, which is beneficial for carrier transport. Under standard solar-lighting conditions, the power conversion efficiency (PCE) of the device increases from 19.13 to 21.36%, and the fill factor is as high as 83.17%. Owing to both the hydrophobicity of DADA molecules and the passivation of ion defects, the PCE of the device remains above 80%, even for the device stored for 500 h in air at a relative humidity of 65%, and the device stability is substantially improved.

Self-Driven Photo-Polarized Water Molecule-Triggered Graphene-Based Photodetector

Flowing water can be used as an energy source for generators, providing a major part of the energy for daily life. However, water is rarely used for information or electronic devices. Herein, we present the feasibility of a polarized liquid-triggered photodetector in which polarized water is sandwiched between graphene and a semiconductor. Due to the polarization and depolarization processes of water molecules driven by photogenerated carriers, a photo-sensitive current can be repeatedly produced, resulting in a high-performance photodetector. The response wavelength of the photodetector can be fine-tuned as a result of the free choice of semiconductors as there is no requirement of lattice match between graphene and the semiconductors. Under zero voltage bias, the responsivity and specific detectivity of Gr/NaCl (0.5 M)W/N-GaN reach values of 130.7 mA/W and 2.3 × 10⁹ Jones under 350 nm illumination, respectively. Meanwhile, using a polar liquid photodetector can successfully read the photoplethysmography signals to produce accurate oxygen blood saturation and heart rate. Compared with the commercial pulse oximetry sensor, the average errors of oxygen saturation and heart rate in the designed photoplethysmography sensor are ~1.9% and ~2.1%, respectively. This study reveals that water can be used as a high-performance photodetector in informative industries.

Hydrophobic-Hydrophilic Block Copolymer Mediated Tuning of Halide Perovskite Photosensitive Device Stability and Efficiency

The polymer additive strategy provides a facile and cost-effective way for passivating defects and trap sites at the grain boundaries and interfaces and acting as a barrier against the external degradation factors in perovskite-based devices. However, limited literature exists discussing the integration of hydrophobic and hydrophilic polymer additives in the form of a copolymer within the perovskite films. The inherent difference in the chemical structure of these polymers and their interaction with perovskite components and the environment leads to critical differences in the respective polymer-perovskite films. The current work utilizes both homopolymer and copolymer strategies to understand the effect of polystyrene (PS) and polyethylene glycol (PEG), two common commodity polymers, over the physicochemical and electro-optical properties of the as-fabricated devices and the distribution of polymer chains across the depth of perovskite films. The hydrophobic PS integrated perovskite devices PS-MAPbI₃, 36 PS-b-1.4-PEG-MAPbI₃, and 21.5 PS-b-20-PEG-MAPbI₃ outperform hydrophilic PEG-MAPbI₃ and pristine MAPbI₃ devices and exhibit higher photocurrent, lower dark currents, and greater stability. A critical difference is also observed in the stability of devices, where rapid decay of performance is observed in the pristine MAPbI₃ films. The deterioration in performance is highly limited for hydrophobic polymer-MAPbI₃ films as they maintain 80% of their initial performance.