Performance Improvement of Lead-Based Halide Perovskites through B-Site Ion-Doping Strategies.

Owing to their excellent properties, lead halide perovskites have attracted extensive attention in the photoelectric field. Presently, the certified power conversion efficiency of perovskite solar cells has reached 25.7%, the specific detectivity of perovskite photodetectors has exceeded 1014 Jones, and the external quantum efficiency of perovskite-based light-emitting diode has exceeded 26%. However, their practical applications are limited by the inherent instability induced by the perovskite structure due to moisture, heat, and light. Therefore, one of the widely used strategies to address the issue is to replace partial ions of the perovskites with ions of smaller radii to shorten the bond length between halides and metal cations, improving the bond energy and enhancing the perovskite stability. Particularly, the B-site cation in the perovskite structure can affect the size of eight cubic octahedrons and their gap. However, the X-site can only affect four such voids. This review comprehensively summarizes the recent progress in B-site ion-doping strategies for lead halide perovskites and provides some perspectives for further performance improvements.

Polypyrrole Serving as Multifunctional Surface Modifier for Photoanode Enables Efficient Photoelectrochemical Water Oxidation.

Conjugated polymer polypyrrole (PPy) with high electrical conductivity and excellent photothermal effect has been adopted as multifunctional surface modifier on ternary metal sulfide (CdIn2 S4 , CIS) photoanode for photoelectrochemical (PEC) water splitting for the first time. As a p-type conducting polymer, PPy forms p-n junction with n-type CIS to relieve the bulk carrier recombination. Besides, the incorporation of Ni ions into PPy matrix further enhances the surface charge carrier transfer at photoanode/electrolyte interfaces. Furthermore, the excellent photothermal effect of PPy produces heat under near-infrared (NIR) irradiation, which can elevate the temperature of CIS photoanode in situ and further enhance the PEC performance. As a result, the optimum CIS/Ni-PPy photoanode shows an obviously enhanced photocurrent density of 6.07 mA cm-2 at 1.23 V versus reversible hydrogen electrode under the irradiation of AM 1.5G combined with NIR light, which is the highest among all the CIS based photoanodes reported to date. The synergetic effect of Ni-PPy significantly suppresses the bulk recombination, decreases the carrier transfer resistance, and accelerates the surface water oxidation dynamics, resulting in high carrier injection efficiency over 80% in the measured potential range. The universality of the multifunctional surface modifier strategy has also been confirmed on metal oxide photoanode.

Embedding of Ti3 C2 Tx Nanocrystals in MAPbI3 Microwires for Improved Responsivity and Detectivity of Photodetector.

Organic-inorganic hybrid MAPbI3 microwires show unique optoelectronic properties for high performances of photodetectors (PDs). However, the defects-assisted nonradiative recombination is harmful for carrier transport, which limits the performances improvement of MAPbI3 microwires PDs. Traditional organic passivation agents effectively combine the surface defects of microwires and also reduce the mobility of overall film based on the perovskite microwires. Therefore, the improvement of internal carrier transport of microwires and the mobility of integrated film simultaneously is a particular challenge for fabrication of performances enhanced perovskite microwires PDs. Here, the Ti3 C2 Tx NCs are fabricated by nonfocus laser irradiation in liquid environment, and hybrids the high conductive NCs in the MAPbI3 microwires. The presence of Ti3 C2 Tx NCs renders defects passivation, enhancement of crystalline orientation, charge transport, and carrier extraction for MAPbI3 microwires, and boots the mobility of microwires based film, leading to about tenfolds enhancement of performances of PDs than that of the control. The maximum responsivity and the detectivity of the Ti3 C2 Tx NCs embedded MAPbI3 microwires PDs reach to 1.70 A W-1 and 7.0 × 1011 Jones in visible window, respectively. The findings suggest that the laser generated high conductive Ti3 C2 Tx NCs is an effective additive for perovskite microwires to fabricate performances enhanced optoelectronics.

Observing Defect Passivation of the Grain Boundary with 2-Aminoterephthalic Acid for Efficient and Stable Perovskite Solar Cells.

Metal halide perovskite solar cells (PSCs), with their exceptional properties, show promise as photoelectric converters. However, defects in the perovskite layer, particularly at the grain boundaries (GBs), seriously restrict the performance and stability of PSCs. Now, a simple post-treatment procedure involves applying 2-aminoterephthalic acid to the perovskite to produce efficient and stable PSCs. By optimizing the post-treatment conditions, we created a device that achieved a remarkable power conversion efficiency (PCE) of 21.09 % and demonstrated improved stability. This improvement was attributed to the fact that the 2-aminoterephthalic acid acted as a cross-linking agent that inhibited the migration of ions and passivated the trap states at GBs. These findings provide a potential strategy for designing efficient and stable PSCs regarding the aspects of defect passivation and crystal growth.

Doping-Induced Amorphization, Vacancy, and Gradient Energy Band in SnS2 Nanosheet Arrays for Improved Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) water splitting is a promising strategy to convert solar energy into hydrogen fuel. However, the poor bulk charge-separation ability and slow surface oxygen evolution reaction (OER) dynamics of photoelectrodes impede the performance. We construct In- and Zn/In-doped SnS2 nanosheet arrays through a hydrothermal method. The doping induces the simultaneous formation of an amorphous layer, S vacancies, and a gradient energy band. This leads to elevated carrier concentrations, an increased number of surface-reaction sites, accelerated surface-OER kinetics, and an enhanced bulk-carrier separation efficiency with a decreased recombination rate. This efficient doping strategy allows to manipulate the morphology, crystallinity, and band structure of photoelectrodes for an improved PEC performance.

Boosting PEC performance of Si photoelectrodes by coupling bifunctional CuCo hybrid oxide cocatalysts.

Silicon (Si) is an attractive candidate for photoelectrochemical (PEC) water splitting because of its small band gap, fast carrier mobility and abundant reserves. However, the PEC performance has been severely limited by the sluggish kinetics of oxygen/hydrogen evolution reaction at the Si photoelectrode/electrolyte interface and poor stability in the aqueous environment. Herein, the bifunctional CuCo hybrid oxides (CuCo-HO) cocatalysts have been integrated with ultrathin TiO2 decorated n-type and p-type Si nanowires (NWs) to simultaneously improve the photoactivity and stability of Si photoelectrodes. The thickness of TiO2 layer, the concentration of CuCo-precursor and the hydrothermal reaction time have been investigated to optimize the PEC performance. The enhancement mechanism is studied and mainly ascribed to the increased light harvesting, small charge transfer resistance and high carrier density of Si NWs/TiO2/CuCo-HO photoelectrodes.

Simultaneous Manipulation of O-Doping and Metal Vacancy in Atomically Thin Zn10 In16 S34 Nanosheet Arrays toward Improved Photoelectrochemical Performance.

The facile hydrothermal synthesis of Zn10 In16 S34 atomically thin nanosheet arrays on fluorine-doped tin oxide glass (FTO) substrates is presented. Through controlling heat treatment in air, O-doping and Zn, S vacancies were simultaneously introduced in Zn10 In16 S34 nanosheets with adjusted phase, morphology, chemical compositions, and energy level distribution. The surface defect states are passivated by depositing ultrathin Al2 O3 film by atomic layer deposition technology. The performance of Zn10 In16 S34 photoanodes is largely improved, with 4.7 times higher current density and reduced onset potential. The experimental results and density functional theory calculations indicate that the enhancement is attributed to the fast photoexcited electron-hole pair separation, decreased surface transfer impedance, prolonged carrier lifetime, and reduced overpotential of oxygen evolution reaction.

Self-Powered, Flexible, and Solution-Processable Perovskite Photodetector Based on Low-Cost Carbon Cloth.

Flexible perovskite photodetectors are usually constructed on indium-tin-oxide-coated polymer substrates, which are expensive, fragile, and not resistant to high temperature. Herein, for the first time, a high-performance flexible perovskite photodetector is fabricated based on low-cost carbon cloth via a facile solution processable strategy. In this device, perovskite microcrystal and Spiro-OMeTAD (hole transporting material) blended film act as active materials for light detection, and carbon cloth serves as both a flexible substrate and a conductive electrode. The as-fabricated photodetector shows a broad spectrum response from ultraviolet to near-infrared light, high responsivity, fast response speed, long-term stability, and self-powered capability. Flexible devices show negligible degradation after several tens of bending cycles and at the extremely bending angle of 180°. This work promises a new technique to construct flexible, high-performance photodetectors with low cost and self-powered capability.

Two-Terminal Perovskite Optoelectronic Synapse for Rapid Trained Neuromorphic Computation with High Accuracy.

Emerging neural morphological vision sensors inspired by biological systems that integrate image perception, memory, and information computing are expected to transform the landscape of machine vision and artificial intelligence. However, stable and reconfigurable light-induced synaptic behavior always relies on independent gateport modulation. Despite its potential, the limitations of uncontrollable defects and ionic characteristics have led to simpler, smaller, and more integration-friendly two-terminal devices being used as sidelines. In this work, the synergy between ion migration barriers and readout voltage is proven to be the key to realizing stable, reconfigurable, and precisely controllable postsynaptic current in two-terminal devices. Following the same mechanism, optical and electrical signal synchronous triggering is proposed to serve as a preprocessing method to achieve a recognition accuracy of 96.5%. Impressively, the gradual ion accumulation during the training process induces photocurrent evolution, serving as a reference for the dynamic learning rate and boosting accuracy to 97.8% in just 10 epochs. The PSC modulation potential under short optical pulse of 20 ns is also revealed. This optoelectronic device with perception, memory, and computation capabilities can promote the development of new devices for future photonic neural morphological circuits and artificial vision.

Pyroelectric-Accelerated Perovskite Photodetector for Picosecond Light Detection and Ranging.

Light detection and ranging (LiDAR) is indispensable in applications such as unmanned aerial vehicles, autonomous driving, and biomimetic robots. However, the precision and available distance of LiDAR are constrained by the speed and sensitivity of the photodetector, necessitating the use of expensive and energy-consuming avalanche diodes. To address these challenges, in this study, a pyroelectricity-based acceleration strategy with 2D-(graded 3D) perovskite heterojunction is proposed to achieve a record high speed (27.7 ns with an active area of 9 mm2, and 176 ps with an active area of 0.2 mm2) and high responsivity (0.65 A W-1) at zero bias. This success is attributed to the unique mechanism where the electrons from the pyroelectric effect at the Cl-rich 2D/3D interface directly recombine with excess holes during light-dark transitions, breaking speed limitations related to carrier mobility and capacitive effect. Furthermore, the introduced pyroelectric effect significantly enhances the photoresponse, resulting in a self-powered external quantum efficiency exceeding 100%. The study also demonstrates precise position detection at the centimeter level. In conclusion, this research presents a pioneering approach for developing high-speed photodiodes with exceptional sensitivity, mitigating energy and cost concerns in LiDAR applications.

Frequency-selective perovskite photodetector for anti-interference optical communications.

Free-space coupling, essential for various communication applications, often faces significant signal loss and interference from ambient light. Traditional methods rely on integrating complex optical and electronic systems, leading to bulkier and costlier communication equipment. Here, we show an asymmetric 2D-3D-2D perovskite structure device to achieve a frequency-selective photoresponse in a single device. By combining two electromotive forces of equal magnitude in the opposite directions, the device output is attenuated to zero under constant light illumination. Because these reverse photodiodes have different response speeds, the device only responds near a certain frequency, which can be tuned by manipulating the 2D perovskite components. The target device achieves an ultrafast response of 19.7/18.3 ns in the frequency-selective photoresponse range 0.8-9.7 MHz. This anti-interference photodetector can accurately transmit character and video data under strong light interference with a source intensity of up to 454 mW cm-2.

Ethylamine Iodide Additive Enables Solid-to-Solid Transformed Highly Oriented Perovskite for Excellent Photodetectors.

Perovskite has been widely applied in the optoelectronic field due to its strong light absorption and high carrier mobility. Maintaining high crystallization is critical to fabricate high-performance perovskite devices, where many methods have been reported, such as the use of additives in precursor solutions. However, there are few reports for the working mechanism of these additives. Herein, a new method to obtain highly crystalline formamidinium-lead triiodide (FAPbI3 ) perovskite films by introducing ethylamine iodide (EAI) into perovskite precursors is reported and a novel working mechanism for such alkyl amine additives in the crystallization process of perovskites is proposed. Unlike traditional liquid-to-solid (L-S) crystallization theory, the research results indicate that EAI affects the solid-to-solid (S-S) transition process from the intermediate yellow phase to the final black phase, and this mechanism is further verified to be universal using other common alkyl amines. A self-powered photodetector based on an as-fabricated FAPbI3 film is fabricated with an external quantum efficiency of over 90%. This work provides a deeper understanding of the perovskite crystallization process.

Multidimensional perovskite solar cells.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted extensive attention, and their certified power conversion efficiency (PCE) has reached 25.5%. However, the instability of the high-efficiency 3-dimensional (3D) perovskite against ambient conditions (moisture, light and thermal) and the existing defects severely limit its practical applications and commercialization. Unlike 3D perovskites, the large hydrophobic spacer cations in low-dimensional (2D, 1D, and 0D) perovskites are able to effectively improve the stability, but they also weaken the light absorption range and hinder charge transport. The construction of a low-dimensional/3D perovskite multidimensional structure, which can combine the advantages of the high stability of low-dimensional perovskites and the superior efficiency of 3D perovskites, is proposed to achieve high efficiency and ultrastability. Moreover, the proper incorporation of low-dimensional perovskite into 3D perovskite can passivate defects and inhibit ion migration. Herein, this article summarizes the recent research progress of low-dimensional/3D perovskite multidimensional structures for PSCs and provides some perspectives toward developing stable and efficient PSCs.

Phase-Transition-Cycle-Induced Recrystallization of FAPbI3 Film in An Open Environment Toward Excellent Photodetectors with High Reproducibility.

Perovskite is an attractive building block for future optoelectronic applications. However, the strict fabrication conditions of perovskite devices impede the transformation of lab techniques into commercial applications. Here, a facile annealing-free posttreatment is proposed to reconstruct the perovskite film to obtain high-performance photodetectors with an optimized production rate. With posttreatment by methylamine thiocyanate, the prefabricated formamidinium-lead triiodide (FAPbI3 ) film will undergo a recrystallization process consisting of a repeating phase-transition-cycle (PTC) between the black and yellow phases of FAPbI3 , which improves the crystal quality and eliminates defects. As a result, some casually prepared or even decomposed perovskite films can be reconstructed, and the dispersion degree of the device performance based on the posttreatment method decreases by ≈21% compared to the traditional antisolvent method. This facile and annealing-free posttreatment will be an attractive method for the future industrial production of perovskite devices.

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.

Atomic Sn-enabled high-utilization, large-capacity, and long-life Na anode.

Constructing robust nucleation sites with an ultrafine size in a confined environment is essential toward simultaneously achieving superior utilization, high capacity, and long-term durability in Na metal-based energy storage, yet remains largely unexplored. Here, we report a previously unexplored design of spatially confined atomic Sn in hollow carbon spheres for homogeneous nucleation and dendrite-free growth. The designed architecture maximizes Sn utilization, prevents agglomeration, mitigates volume variation, and allows complete alloying-dealloying with high-affinity Sn as persistent nucleation sites, contrary to conventional spatially exposed large-size ones without dealloying. Thus, conformal deposition is achieved, rendering an exceptional capacity of 16 mAh cm-2 in half-cells and long cycling over 7000 hours in symmetric cells. Moreover, the well-known paradox is surmounted, delivering record-high Na utilization (e.g., 85%) and large capacity (e.g., 8 mAh cm-2) while maintaining extraordinary durability over 5000 hours, representing an important breakthrough for stabilizing Na anode.

2D Ruddlesden-Popper Perovskite with Ordered Phase Distribution for High-Performance Self-Powered Photodetectors.

2D Ruddlesden-Popper perovskites exhibit great potential in optoelectronic devices for superior stability compared with their 3D counterparts. However, to achieve a high level of device performance, it is crucial but challenging to regulate the phase distribution of 2D perovskites to facilitate charge carrier transfer. Herein, using a solvent additive method (adding a small amount of dimethyl sulfoxide (DMSO) in N,N-dimethylformamide (DMF)) combined with a hot-casting process, the phase distribution of (PEA)2 MA3 Pb4 I13 (PEA+  = C6 H5 CH2 CH2 NH3 + , MA+  = CH3 NH3 + ) perovskite can be well controlled and the Fermi level of perovskites along the film thickness direction can achieve gradient distribution. The increased built-in potential, oriented crystal, and improved crystal quality jointly contribute to the high photoresponse of devices in the entire response spectrum range. The optimum device exhibits a characteristic detection peak at 570 nm with large responsivity/detectivity (0.44 A W-1 /3.38 × 1012 Jones), ultrafast response speed with a rise/fall time of 20.8/20.6 µs, and improved stability. This work suggests the possibility of manipulating the ordered phase distribution of 2D perovskites toward high-performance and stable optoelectronic conversion devices.

Moisture-Triggered Self-Healing Flexible Perovskite Photodetectors with Excellent Mechanical Stability.

Flexible devices are urgently required to meet the demands of next-generation optoelectronic devices and metal halide perovskites are proven to be suitable materials for realizing flexible photovoltaic devices. However, the tolerance to moisture corrosion and repeated mechanical bending remains a critical challenge for flexible perovskite devices. Herein, a self-healing formamidinium lead iodide (FAPbI3 ) film is fabricated to cure mechanical damage by absorbing moisture from the surrounding environment. A poly(vinyl alcohol) microscaffold is designed not only to stabilize the black phase of the FAPbI3 film but also to endow it with self-healing ability in a humid environment. The photodetector based on a self-healing film exhibits a high responsivity of 11.3 A W-1 and recovers to over 90% of the initial responsivity after the self-healing process. This work provides an effective self-healing strategy to stabilize the operation of flexible perovskite devices under normal high-humidity environmental conditions.

Intermediate-Adduct-Assisted Growth of Stable CsPbI2 Br Inorganic Perovskite Films for High-Efficiency Semitransparent Solar Cells.

Thanks to the tunable bandgap and excellent photoelectric characteristics, perovskites have been widely used in semitransparent solar cells (ST-SCs). Most works present unsatisfactory power conversion efficiencies (PCEs) through reducing the thickness of the perovskite films because there is a trade-off between PCE and average visible transmittance (AVT). As a consequence, most PCEs are less than 12% when the AVT is higher than 20% due to the limited voltage (Voc ) and short-circuit current (Jsc ). Herein, a strategy of intermediate adduct (IMAT) engineering is developed to improve the film quality of the inorganic perovskite CsPbI2 Br, which is a challenging issue to limit its performance of efficiency and stability. A normal n-i-p-structured PSC based on the optimal CsPbI2 Br film delivers a PCE of 16.02% with excellent stability. Furthermore, through optimizing the electrode type and interface, the ST-PSC shows a high Voc larger than 1.2 V and the PCE reaches 14.01% and 10.36% under an AVT of 31.7% and 40.9%, respectively. This is the first demonstration of a CsPbI2 Br ST-PSC, and it outperforms most of other types of perovskites.

Nested Inverse Opal Perovskite toward Superior Flexible and Self-Powered Photodetection Performance.

Flexible and self-powered perovskite photodetectors have attracted tremendous research interests due to their applications in wearable and portable devices. However, the conventional planar structured photodetectors are always accompanied with limited device performance and undesired mechanical stability. Herein, a nested inverse opal (NIO) structured perovskite photodetector via a facile template-assisted spin-coating method is reported. The coupling effect of enhanced light capture, increased carrier transport, and improved perovskite film quality enables NIO device to exhibit superior photoresponse performance. The NIO photodetector exhibits a high responsivity of 473 mA W-1 and detectivity up to 1.35 × 1013 Jones at 720 nm without external bias. The NIO structure can efficiently release mechanical stress during the bending process and the photocurrent has no degradation even after 500 cycles of bending. Moreover, the unencapsulated NIO device can operate for over 16 d under ambient conditions, presenting a significantly enhanced environmental stability compared to the planar device. This work demonstrates that deliberate structural design is an effective avenue for constructing self-powered, flexible, and stable optoelectronic devices.