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Recently, conductive-bridging memristors based on metal halides, such as halide perovskites, have been demonstrated as promising components for brain-inspired hardware-based neuromorphic computing. However, realizing devices that simultaneously fulfill all of the key merits (low operating voltage, high dynamic range, multilevel nonvolatile storage capability, and good endurance) remains a great challenge. Herein, we describe lead-free cesium halide memristors incorporating a MoO

SUMMARYRuddlesden-Popper (RP) perovskites are two-dimensional semiconductors for high performance devices. In this work, we report a long in-plane charge carrier diffusion length in 2D RP perovskite single crystals probed by scanning photocurrent microscopy. Carrier diffusion lengths of 7~14 µm are observed when the number of PbI6-2 octahedrons between organic spacers increases from 1 to 3. By detailed light intensity and electric field-dependent photocurrent measurements, we attribute the observed long diffusion length to the dominating dissociated free carrier transport. This is further validated by time-resolved photoluminescence measurements where the decay lifetime increases in the presence of an electric field. From our experiments, we conclude that the in-plane transport in RP perovskites is efficient because of the partial free carrier generation overcoming strong excitonic effects. Our results suggest that semiconducting devices fabricated from RP perovskite single crystals can be as efficient as their 3D counterparts.

Herein, we report a sequential deposition procedure to passivate the surface of a hybrid mixed cationic tin perovskite (E1G20) with phenylhydrazinium thiocyanate (PHSCN) dissolved in trifluoroethanol solvent. The photoluminescence lifetime of the PHSCN film was enhanced by a factor of 6, while the charge-extraction rate from perovskite to C60 layer was enhanced by a factor of 2.5, in comparison to those of the E1G20 film. A slow surface passivation was observed; the performance of the PHSCN device improved upon increasing the storage period to attain an efficiency of 13.5% for a current-voltage scan in the forward bias direction. An inverted effect of hysteresis was observed in that the efficiency of the forward scan was greater than that of the reverse scan. An ion-migration model as a result of the effect of the phenylhydrazinium surface passivation is proposed to account for the observed phenomena. The device was stable upon shelf storage in a glovebox for 3000 h.

Inverted-structure metal halide perovskite solar cells (PSCs) have attractive advantages like low-temperature processability and outstanding device stability. The two-step sequential deposition method shows the benefits of easy fabrication and decent performance repeatability. Nevertheless, it is still challenging to achieve high-performance inverted PSCs with similar or equal power conversion efficiencies (PCEs) compared to the regular-structure counterparts via this deposition method. Here, an improved two-step sequential deposition technique is demonstrated via treating the bottom organic hole-selective layer with the binary modulation system composed of a polyelectrolyte and an ammonium salt. Such improved sequential deposition method leads to the spontaneous refinement of up and buried interfaces for the perovskite films, contributing to high film quality with significantly reduced defect density and better charge transportation. As a result, the optimized PSCs show a large enhancement in the open-circuit voltage by 100 mV and a dramatic lift in the PCE from 18.1% to 23.4%, delivering the current state-of-the-art performances for inverted PSCs. Moreover, good operational and thermal stability is achieved upon the improved inverted PSCs. This innovative strategy helps gain a deeper insight into the perovskite crystal growth and defect modulation in the inverted PSCs based on the two-step sequential deposition method.

Perovskites doped with chlorine (Cl-), which are usually fabricated using the solution process, can effectively improve the stability and carrier mobility. Compared with the low tolerance of the solution process that relies mostly on personal skill, thermal evaporation is an important method for large-scale production of perovskite solar cells but the production cost is high. In this study, the sandwich evaporation-solvent annealing (SE-SA) method is proposed. Using sandwich evaporation with a low-cost chamber of the sandwich evaporation technique (SET) made in the laboratory and with the help of DMSO steam-assisted crystallization, we have successfully produced chlorine-containing perovskite solar cells with a high crystallinity and a high efficiency of 15.1% with Voc = 0.98 V, Jsc = 21.94 mA/cm2, FF = 74.29%, and Rs = 3.66 Ω·cm2, which can greatly reduce the production cost. It is worth mentioning that all the processes are carried out outside a glove box, which makes it possible for large-scale production of chlorine-containing perovskite solar cells by evaporation.

Perovskite nanocrystals are exceptional candidates for light-emitting diodes (LEDs). However, they are unstable in the solid film and tend to degrade back to the bulk phase, which undermines their potential for LEDs. Here we demonstrate that perovskite nanocrystals stabilized in metal–organic framework (MOF) thin films make bright and stable LEDs. The perovskite nanocrystals in MOF thin films can maintain the photoluminescence and electroluminescence against continuous ultraviolet irradiation, heat and electrical stress. As revealed by optical and X-ray spectroscopy, the strong emission originates from localized carrier recombination. Bright LEDs made from perovskite-MOF nanocrystals are demonstrated with a maximum external quantum efficiency of over 15% and a high brightness of over 105 cd m−2 after the device reaches stabilization. During LED operation, the nanocrystals can be well preserved, free of ion migration or crystal merging through protection by the MOF matrix, leading to a stable performance over 50 hours. The use of metal–organic frameworks helps protect perovskite nanocrystals, resulting in bright, stable light-emitting diodes.

Image-sensor technology is the foundation of many emerging applications, where the photodetector is designed to interact with incoming photons that have specific colors or wavelengths. A color filter is therefore crucial to enable the selective spectral response of the photodetector and to eliminate the crosstalk interference resulting from ambient lights. Unfortunately, a reduced detection sensitivity of the photodetector is inevitable due to an imperfect light filtering, which greatly limits the practical applications of selective-response photodetectors. Herein, we demonstrate a bulk-heterojunction (BHJ) organic composite featuring a self-filtering light responsive characteristic. Through a careful optimization of the BHJ film, the organic photodetector (OPD) demonstrates a high-selective spectral response to the infrared (IR) radiation without the need of applying a color filter. As a result, the self-filtering top-illuminated OPD exhibits a narrowband external quantum efficiency (EQE) of 53% with a narrow full width at half-maximum (fwhm) of 56 nm centering at 1080 nm. A high responsivity of 0.46 A W

A polymer-based hole-transporting layer (HTL) with a tunable work function and highest occupied molecular orbital (HOMO) position was demonstrated to effectively optimize the anode junctions of optoelectronic devices. Herein, the perfluorinated ionomer (PFI) was utilized to realize the synthesis of a well-dispersed poly(3,4-ethylene dioxythiophene) (PEDOT) colloid solution, which could be subsequently cast into an efficient HTL. According to the time-of-flight secondary-ion mass spectroscopy and ultraviolet photoelectron spectroscopy analysis, a uniform, interpenetrating PEDOT network with a deep-lying HOMO position could be obtained in the PEDOT:PFI layer. For solar cells, since a deep-lying HOMO position of the HTL was favorable for minimizing the hole injection barrier, a superior organic photovoltaic efficiency of 15.1% and a perovskite solar cell efficiency of 17.8% were achieved. As for organic photodetectors, a deep-lying HOMO position of the HTL was able to reduce the dark current density (JD) by blocking the leakage current under a reverse bias. Utilizing the PEDOT:PFI with an optimized PFI content, an extremely low JD of 6.2 nA cm−2 with an external quantum efficiency of 67% at 1000 nm wavelength was achieved, which sets a benchmark for the emerging near infrared sensing technologies.

Perovskite solar cells (PSCs) employing organic–inorganic hybrid lead perovskite have attracted much attention as promising next generation solar cells because of their low fabrication cost and extremely high power conversion efficiency (PCE). Exploring new perovskite materials and additives is one of the effective strategies to improve the performance of PSCs. Here, we synthesized formamide iodide (FoAI) and applied it as both a cation material and additive. Although it was revealed that FoAI is not incorporated in the A-site of the perovskite structure, we found that the FoAI additive suppresses δ-FAPbI3 formation and improved the performance of FAPbI3 based PSCs. The PCE was improved from 12.29% to 14.49% by adding 5 mol% of FoAI in the precursor solution. Meanwhile, we found that FoAI additive can also improve the performance of triple-cation PSCs. We believe that FoAI is one of the promising additives to boost the PCE of PSCs without any influence on the composition of the perovskite materials.

Defects at the bulk grain boundaries and heterojunction interfaces could dictate the power losses of perovskite solar cells (PSCs) during the operation process, which are regarded as major roadblocks towards further development of this emerging photovoltaic technology. The common modulation strategies reported for the state-of-the-art cells cannot concurrently heal the defects located at the grain boundaries and interfaces. Herein, a depth-dependent manipulation strategy is demonstrated to concurrently modulate the bulk and interfacial defects in the perovskite films. According to the distinct penetrability of the employed binary modulators within the polycrystalline perovskite film, one of the modulators can penetrate through the bulk to the buried interface, accompanied by bulk and buried interface defect healing, while the other remains to anchor atop the surface along with the surface defect modulation, assuring simultaneous defect management from the interfaces to the bulk. As a result, the mitigated non-radiative losses and the improved charge transport of the modulated perovskite film boost the efficiency of PSCs from 21.79% to 24.36%. This universally effective depth-dependent manipulation strategy provides new insights into spatial defect modulation, which would open up a promising way for defect modulator design for highly efficient perovskite optoelectronic devices.

Most chemical vapor deposition methods for transition metal dichalcogenides use an extremely small amount of precursor to render large single-crystal flakes, which usually causes low coverage of the materials on the substrate. In this study, a self-capping vapor-liquid-solid reaction is proposed to fabricate large-grain, continuous MoS2 films. An intermediate liquid phase-Na2Mo2O7 is formed through a eutectic reaction of MoO3 and NaF, followed by being sulfurized into MoS2. The as-formed MoS2 seeds function as a capping layer that reduces the nucleation density and promotes lateral growth. By tuning the driving force of the reaction, large mono/bilayer (1.1 mm/200 μm) flakes or full-coverage films (with a record-high average grain size of 450 μm) can be grown on centimeter-scale substrates. The field-effect transistors fabricated from the full-coverage films show high mobility (33 and 49 cm2 V−1 s−1 for the mono and bilayer regions) and on/off ratio (1 ~ 5 × 108) across a 1.5 cm × 1.5 cm region., Here, the authors develop a self-capping vapour-liquid-solid reaction to fabricate large-grain continuous MoS2 films, whereby an intermediate liquid phase-Na2Mo2O7 is formed through a eutectic reaction of MoO3 and NaF, followed by sulphurisation into MoS2.

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) has been used for gaining insights into perovskite solar cells (PSCs). However, the importance of selecting ion beam parameters to eliminate artifacts in the resulting depth profile is often overlooked. In this work, significant artifacts were identified with commonly applied sputter sources, i.e., an O

High photovoltage generation from a photoelectrode is important for efficient solar driven water splitting. Here, we report a thermal treatment process that greatly enhances photovoltage generation...

Unraveling the reaction mechanism behind the CO2 reduction reaction (CO2RR) is a crucial step for advancing the development of efficient and selective electrocatalysts to yield valuable chemicals. To understand the mechanism of zinc electrocatalysts toward the CO2RR, a series of thermally oxidized zinc foils is prepared to achieve a direct correlation between the chemical state of the electrocatalyst and product selectivity. The evidence provided by in situ Raman spectroscopy, X-ray absorption spectroscopy (XAS) and X-ray diffraction significantly demonstrates that the Zn(II) and Zn(0) species on the surface are responsible for the production of carbon monoxide (CO) and formate, respectively. Specifically, the destruction of a dense oxide layer on the surface of zinc foil through a thermal oxidation process results in a 4-fold improvement of faradaic efficiency (FE) of formate toward the CO2RR. The results from in situ measurements reveal that the chemical state of zinc electrocatalysts could dominate the product profile for the CO2RR, which provides a promising approach for tuning the product selectivity of zinc electrocatalysts.

The growth process control (GPC) method, a new method which is better than thermal evaporation, for producing high-crystallinity perovskites by controlling the growth time in a low vacuum, is explored in this work. Inspired by evaporation technology, GPC is an effective method for modifying traditional thermal evaporation and for controlling the crystal growth of perovskite CH3NH3I3. Compared to fabrication with the process of co-evaporation, the MAPbI3 perovskite solar cell fabricated by GPC has high uniformity and film coverage. All of the manufacturing is carried out outside of the glove box. It provides an easy and effective way for perovskite fabrication for industrialization. Here, after using GPC to form perovskite solar cells, the residual methylammonium iodide (MAI) and PbI2 which is produced by the evaporation process can react completely, observed by time of flight secondary ion mass spectrometry (TOF-SIMS). Finally, formed by GPC, perovskite solar cells exhibit high performance and fewer crystal defects. The electron and hole recombination is greatly reduced. Through the GPC method, the Jsc and the filling factor are improved with the increase of time after the fabrication. The power conversion efficiency was increased from 11.12% to 16.4%.

The benefits of excess PbI

In this study, a nanocomposite coating composed of polydopamine, functionalized poly(3,4-ethylenedioxythiophene) (PEDOT), and silver nanoparticles (AgNPs) was synthesized through layer-by-layer deposition. Biomimitic polydopamine and hydroxyl-functionalized PEDOT were used to enhance the adhesion strength. The deposition of PEDOT functionalized with zwitterionic phosphorylcholine can contribute to the antifouling property. After immersion in the AgNO

Perovskites doped with chlorine (Cl

Heterogeneous catalysis based on air-stable lanthanide complexes is relatively rare, especially for electrochemical water oxidation and reduction. Therefore, it is highly desired to investigate the synergy caused by cocatalysts on the lanthanide complex family for heterogeneous catalysis because of their structural diversity, air/moisture insensitivity, and easy preparation under an air atmosphere. Two mononuclear and three dinuclear dysprosium complexes containing a series of Schiff-base ligands have been demonstrated as robust electrocatalysts for triggering heterogeneous water oxidation in alkaline solution, in which the complex [Dy2(hmb)2(OAc)4]·MeCN(3) was revealed to have the best activity toward heterogeneous water oxidation among all five complexes in the present study. The molecular activation of dysprosium complexes has also been investigated with a series of N-containing heterocyclic additives [i.e., 4-(dimethylamino)pyridine (DMAP), bis(triphenylphosphine)iminium chloride ([PPN]Cl), indole, and quinoline]. In particular, the corresponding overpotential was effectively enhanced by 211 mV (at a current density of 10 mA cm-2) with the assistance of DMAP. On the basis of electrochemical and ex situ/in situ spectroscopic investigations, the best catalyst, DMAP-complex 3 on a carbon paper electrode, was confirmed with well-maintained molecular identity during heterogeneous water oxidation free of forming any dysprosium oxide and/or undesired products.

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approaches 19%, increasing research attention is being paid to enhancing the device's long-term stability. In this study, a robust interface engineering of graphene oxide nanosheets (GNS) is expounded on improving the thermal and photostability of non-fullerene bulk-heterojunction (NFA BHJ) OPVs to a practical level. Three distinct GNSs (GNS, N-doped GNS (N-GNS), and N,S-doped GNS (NS-GNS)) synthesized through a pyrolysis method are applied as the ZnO modifier in inverted OPVs. The results reveal that the GNS modification introduces passivation and dipole effects to enable better energy-level alignment and to facilitate charge transfer across the ZnO/BHJ interface. Besides, it optimizes the BHJ morphology of the photoactive layer, and the N,S doping of GNS further enhances the interaction with the photoactive components to enable a more idea BHJ morphology. Consequently, the NS-GNS device delivers enhanced performance from 14.5% (control device) to 16.5%. Moreover, the thermally/chemically stable GNS is shown to stabilize the morphology of the ZnO electron transport layer (ETL) and to endow the BHJ morphology of the photoactive layer grown atop with a more stable thermodynamic property. This largely reduces the microstructure changes and the associated charge recombination in the BHJ layer under constant thermal/light stresses. Finally, the NS-GNS device is demonstrated to exhibit an impressive T

The composite electron transporting layer (ETL) of metal oxide with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) prevents perovskite from metal electrode erosion and increases p-i-n perovskite...

Unraveling the reaction mechanism behind the CO

Tin-based perovskite, which exhibits narrower bandgap and comparable photophysical properties to its lead analogs, is one of the most forward-looking lead-free semiconductor materials. However, the poor oxidative stability of tin perovskite hinders the development toward practical application. In this work, the effect of pseudohalide anions on the stability and emission properties of single-layer 2D tin perovskite nanoplates with chemical formula TEA

The traditional way to stabilize α-phase formamidinium lead triiodide (FAPbI

Sol–gel metal oxide films are an important type of functional materials for energy technologies and beyond owing to their versatile properties and ease of processing, but their applications are limited by the typically required high sintering temperatures. This study reports a novel phenomenon where the sintering temperatures of sol–gel metal oxide films were substantially lowered when a metal phase was embedded within the sol–gel precursor films. Morphological and compositional analyses revealed that the reduction in sintering temperatures was enabled by a mechanism similar to the metal-induced crystallization (MIC) process, with a distinction that catalysis of sol–gel reactions occurred alongside the induction of crystallization. We observed this catalytic MIC (c-MIC) mechanism in a variety of sol–gel material systems including NixO with embedded Au or Ag; TiOx with embedded Ni, Au, or Pt; and SnOx with embedded Ni. Based upon this concept, we demonstrated highly efficient flexible and rigid organic/inorganic hybrid perovskite solar cells (PSCs) using a low-temperature-sintered NixO film embedded with Au nanoislands as the hole-transporting layer (HTL). The c-MIC mechanism reduced the sintering temperature of the Au-embedded NixO HTL by 100 °C, making the NixO process compatible with plastic substrates while allowing the NixO HTL to retain more NiOOH surface groups, which enhanced hole collection and improved the quality of the perovskite layer. Thanks to the advantages of the c-MIC NixO film, the flexible and rigid PSCs achieved high power conversion efficiencies of up to 15.9 and 19.0%, respectively, which were sustained for >1200 h at 65 °C and 65% relative humidity. Our findings provide a practical route for low-temperature fabrication of high-quality oxide functional films by solution-based sol–gel processes, which will be valuable to a wide variety of applications in addition to thin film solar cells.

A carrier transport layer and its interfacial effects on an organometal halide perovskite light harvesting layer play an influential factor in either photovoltaic performance or long-term stability of a perovskite solar cell (OHPSC). Although the understandings of the carrier transport layers and interfacial effects on regular structured OHPSCs have been explored, knowledge of an interface between hole transport layer of NiOx and perovskite in an inverted OHPSC is still necessary to be developed. Here, we performed a universal NiOx film with the sequential passivation strategy of NiCl2 (SPS-NiCl2 treatment) for either wide bandgap or narrow bandgap of OHPSCs. The SPS-NiCl2 treated NiOx film not only implements the passivation at the perovskite layer/NiOx film interface but also confers itself a gradient energy level of valance band inducing by chloride. Comprehensive characterizations reveal that the SPS-NiCl2 treated NiOx film suppresses non-radiative recombination at the interface and enlarges the splitting of the quasi-Fermi level at the interfaces. The photoconversion efficiency (PCE) of the champion device comprised of the SPS-NiCl2 treated NiOx film can achieve 19.53% with a record Voc of 1.16 V, the lowest Voc deficit of 390 mV in NiOx based inverted OHPSCs. The corresponding devices with encapsulation also exhibit superior long-term stability, and over 80% of initial PCE can be maintained after 1500 h damp-heat test. This study sheds the light on managing the interfacial issues of an inverted OHPSC and offers a feasible path to develop a universal hole transport layer for perovskite layers with different energy bandgap.