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Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenyl-amine)9,9′-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4- tert -butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.

All-inorganic perovskite nanocrystals (NCs) are promising candidates for light-emitting diodes (LEDs) owing to their excellent optoelectronic properties. However, the pure-red perovskite LEDs (PeLEDs) available today made from mixed-halide CsPb(Br/I)

With the development of perovskite photodetectors, integrating photodetectors into array image sensors is the next target to pursue. The major obstacle to integrating perovskite photodiodes for dynamic imaging is the optoelectrical crosstalk among the pixels. Herein, a perovskite photodiode-blocking diode (PIN-BD) crossbar array with pixel-wise rectifying property by the vapor deposition method is presented. The PIN-BD shows a large rectification ratio of 3.3 × 10

Metal halide perovskite light emitting diodes (PeLEDs) have recently experienced rapid development due to the tunable emission wavelengths, narrow emission linewidth and low material cost. To achieve state-of-the-art performance, the high photoluminescence quantum yield (PLQY) of the active emission layer, the balanced charge injection, and the optimized optical extraction should be considered simultaneously. Multiple chemical passivation strategies have been provided as controllable and efficient methods to improve the PLQY of the perovskite layer. However, high luminance under large injection current and high external quantum efficiency (EQE) can hardly be achieved due to Auger recombination at high carrier density. Here, we decreased the electron injection barrier by tuning the Fermi-level of the perovskite, leading to a reduced turn on voltage. Through molecular doping of the hole injection material, a more balanced hole injection was achieved. At last, a device with modified charge injection realizes high luminance and quantum efficiency simultaneously. The best device exhibits luminance of 55,000 cd m−2, EQE of 8.02% at the working voltage of 2.65 V, current density of 115 mA cm−2, and shows EQE T50 stability around 160 min at 100 mA cm−2 injection current density.

The hydrogen transfer reaction is one of the key chemical processes of coal conversion. The elucidation of the hydrogen transfer mechanism is essential for rational control of the properties and di...

The device stability and toxic-solvent-free processing are indispensable development to industrialize organometal halide perovskite solar cells. In this work, the conventional top surface of vapor prepared 3D-MAPbI3 was replaced by 2D-(BA)2(MA)n‐1PbnI3n+1 perovskite platelet via molecular substitution from MA (CH3NH) to BA (C4H9NH2). Our fully vapor process fabricated a 3D-2D perovskite heterojunction for solar cell application, realizing the power conversion efficiency as high as 16.50% and the average one as 15.40%. Furthermore, unencapsulated devices can sustain their 81% efficiency after 30 days under 55% RH, and also 74% efficiency after 30 days under 80 °C heat stress. Stability of humidity resistance arises from the reduced n value of 2D perovskite caused by the surface reaction of moisture, and the improvement of thermal stability comes from the buffering of MA molecules release. Meanwhile, the fabrication of large scale device with high efficiency is also demonstrated in our experiment.

Ruddlesden–Popper perovskites (RPPs) have attracted intense attention owing to their superior stability. However, the interspace and weak interaction between the inorganic layers inhibits direct ch...

In the present work, a novel method has been proposed, which can be used for generating carbon nanotubes (CNTs) using coal as the raw material and potassium hydroxide as the catalyst precursor. The results of Fourier Transform Infrared (FTIR) spectroscopy indicated that the groups of CH3, CH2 contained in the coal gradually disappeared during the potassium catalyzed pyrolysis. Raman analysis showed that the graphitization degree of catalytic pyrolysis products of raw coal was high, and the ratio of the intensities of G and D peaks (IG/ID) was 3.0. The results of Scanning Electron Microscope (SEM) showed that there were many CNTs in the product. The Transmission Electron Microscopy (TEM) showed that these CNTs had different shapes (linear or curved) and have good graphite crystal structure with a wall number of 18–65 layers and a diameter of 20–155 nm. The potassium catalyst has the dual function of catalyzing the formation of CNTs and etching large molecular structure to generate carbon source. The formation process of CNTs is as follows: coal takes pyrolysis to produce small carbon-containing molecules such as CH4, and the small carbon-containing molecules formed CNTs through catalytic cracking under the action of catalyst. A “stepwise growth” model of CNTs was established.

Study question To compare the changing peripheral levels of inflammation-related cytokine profile during a 9-day period after blastocyst transfer between women who did and did not conceive. Summary answer:Successful implantation is associated with transient increase in serum pro-inflammatory cytokine profile followed by a switch to anti-inflammatory cytokine profile prior to confirmation of pregnancy.What is known already: Immunomodulation is thought to be important for the prevention of rejection of the implanting semi-allograft embryo and successful establishment of pregnancy. A successful pregnancy is characterized by a dominance of anti-inflammatory cytokine profile in the peripheral blood in the first and second trimesters of pregnancy. It is achieved by a complex interplay between various immune cells and cytokines at the fetal-maternal interface, among which the key-players are interleukine–10 (IL–10) and transforming growth factor-β1 (TGF-β1). The circulating inflammatory response in the first few days after embryo transfer to the pathophysiology of implantation failure remains unclear. Study design, size, duration: This prospective observational and longitudinal study on 47 women with infertility was performed in an in vitro fertilization unit from December 2018 to August 2019. The amounts of a range of cytokines was measured on serial blood samples obtained during a 9-day period after blastocyst transfer. Participants/materials, setting, methods Serial blood samples were obtained on the day of embryo transfer, and 3, 6, and 9 days afterward for measurement of serum interferon gamma (IFN-γ), tumor necrosis factor alpha, interleukin (IL)–2, IL–4, IL–10, IL–12, IL–13, IL–17, IL–18, and IL–22 using cytometric bead arrays; transforming growth factor beta 1 (TGF-β1) was measured using commercial enzyme-linked immunosorbent assay kits. Main results and the role of chance The cytokine profile was similar between the women who conceived and those who did not on the day of blastocyst transfer. In women who conceived, IFN-γ and IL–17 (pro-inflammatory cytokines) exhibited a transient and significant increase on day 3 after blastocyst transfer, which decreased to the baseline levels by day 6. Meanwhile, IL–10 (anti-inflammatory cytokine) was increased significantly on days 6 and 9, and TGF-β1 (anti-inflammatory cytokine) was increased significantly on day 9 after blastocyst transfer. In women who did not conceive, there was a more pronounced increase in IFN-γ and IL–17 (pro-inflammatory cytokines) on day 3, which was sustained on days 6 and 9 without a switch to an anti-inflammatory cytokine profile. Among women who conceived after blastocyst embryo transfer, there was a transient and modest increase in serum pro-inflammatory cytokine profile (IFN-γ and IL–17) 3 days after blastocyst transfer, which was followed by a switch to anti-inflammatory cytokine profile (increase IL–10 and TGF-β1) by 6 days after blastocyst transfer and the latter increase was sustained 9 days after blastocyst transfer, when pregnancy was confirmed. Limitations, reasons for caution This is an observational study on peripheral blood cytokine levels, so it is not possible to draw conclusions if the implantation failure is due primarily to failure of the embryo to elicit a trigger for the switch or failure of maternal response to a normal trigger released by the embryo. Wider implications of the findings: The characteristic change in peripheral cytokine profile during successful implantation, well before confirmation of pregnancy, may provide an opportunity to develop serum biomarkers to monitor implantation and to understand the mechanism of its failure, especially in women who experience recurrent implantation failure after IVF. Trial registration number Not applicable

Long-term stability of organic-inorganic hybrid perovskite solar cells (PSCs) is inhibited by ion diffusion. Herein, we introduce a thermally stable and hydrophobic silicone resin layer with a network structure as an interfacial layer between the perovskite and the hole-transporting layer (HTL). Experimental and theoretical investigations confirm that the small Si-O-Si unit in the network forms both Si-I and Pb-O bonds with the perovskite surface, which physically and chemically inhibit the diffusion and self-release of iodine. Besides, the silicone resin layer suppresses the thermal crystallization of spiro-OMeTAD and optimizes the interfacial energy level alignment for hole extraction. The power conversion efficiency (PCE) of a perovskite solar cell with a silicone resin layer is improved to 21.11%. The device maintains more than 90.1% of its original PCE after 1200 h under 85 °C thermal stress, 99.6% after 2000 h under RH ∼55 ± 5%, and 83% of its original PCE after light soaking in air for 1037 h.

Herein, we report two novel derivatives of hexabenzoperylene (HBP) that are functionalized with ester groups. Methyl acetate functionalized HBP (1) in single crystals self-assembles into a supramolecular nanosheet, which has a two-dimensional π-stack of HBP sandwiched between two layers of ester groups. With the same self-assembly motif, active ester-functionalized HBP (2) in field effect transistors has enabled differentiation of tertiary amines from primary and secondary amines, in agreement with the fact that active ester reacts with primary and secondary amines but not with tertiary amines to form amides.

All-inorganic perovskite CsPbI2Br usually requires a high fabrication temperature (higher than 200 °C) and suffers from an unwanted phase transition from a photo-active cubic phase to a photo-inactive orthorhombic phase. Here, we demonstrate an effective anti-solvent-free route to simultaneously stabilize the cubic phase and lower the fabrication temperature of perovskite solar cells with guanidinium (GA) cation doping. It is suggested that a trace amount of GA in the precursor could enter the substitutional sites to stabilize the cubic phase by relaxing the lattice strain and forming strong hydrogen bonds. State-of-the-art in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements reveal that GA could advance the crystallization of the cubic phase, indicating that the formation of the perovskite cubic phase experiences a lowered energy barrier with the assistance of GA, thereby resulting in a significant decrease of the fabrication temperature. An efficiency as high as 14.34% was achieved at a low fabrication temperature of 140 °C. With the help of GA, the device maintains ∼94% of its initial efficiency after being stored for 1000 h.

Vapor reaction is one of the major methods used for large-scale fabrication of high-quality organic–inorganic halide perovskite solar cells, but its detailed process is rarely investigated. In this study, the thermal and illumination effects on PbI2 and its transformation to CH3NH3PbI3 (MAPbI3) under CH3NH3I (MAI) vapor were investigated. Atomic shifting of the PbI2 layer was observed, which caused the generation of defects and distortion in PbI2 without breaking the phase structure. The reaction with MAI started with decoupling of PbI2 layers and formation of nanoislands and then, the transformation of PbI2 to MAPbI3 proceeded randomly on the surface from top to bottom. Additional illumination of the reaction suppressed the transformation, causing the generation of PbI2 nano-walls along [100] and [010] directions, leading to decrease in power conversion efficiency.

Summary The expensive and unstable organic hole transport layer (HTL) is one of the crucial problems that hampers the wide application of perovskite solar cells. Here, an MAPbI3-(BA)2(MA)n−1PbnI3n+1 3D-2D perovskite-perovskite planar heterojunction (PPPH) through a facile BAI and MAPbI3 interfacial ion exchange process was conducted. A graded band structure was formed for efficient charge separation, and the conductivity of the 2D perovskite can be tuned by extrinsic FA incorporation, which provides effective conducting channels for holes, making the modified 2D perovskite layer a promising and stable HTL. Optimized solar cells based on 3D-2D PPPH showed a champion power conversion efficiency (PCE) of 13.15% initially and 16.13% after thermal aging, and could maintain 71% output for 50 days under 65% humidity, and 74% for 30 days under 85°C, without encapsulation. This work points to realize low cost and ambient compatible PPPH solar cells with high PCE and robust stability.

Summary One challenge in tailoring organic semiconductors for sensing applications is that the introduction of reactive groups or binding sites usually impairs π-π interactions. To meet this challenge, this study puts forth an unusual type of π stacking that allows a variety of functional groups to be grafted onto organic semiconductors without sacrificing π-π interactions in the solid state. As a result of this type of π stacking, the self-assembly of functionalized hexabenzoperylenes (HBPs) provides a general sensing platform for various chemical and biological species. This supramolecular platform, in a device integrating an organic field-effect transistor channel and a microfluidic channel, has enabled highly sensitive and selective detection of fluoride ions and streptavidin in water when HBPs are equipped with a cleavable Si–O bond and a biotin moiety, respectively.

Surface passivation has played a critical role for efficient and stable perovskite solar cells by reducing surface defects, promoting charge transport, and preventing the penetration of degrading agents. State-of-the-art passivation approaches mainly rely on the formation of a two-dimensional (2D) perovskite layer or the deposition of an ultrathin layer based on the molecular design. Here, we demonstrated a novel nanocrystal-pinning passivation by dripping 2-bromoethyltrimethylammonium bromide (BETAB) colloidal solution onto perovskite films. Theoretical simulation and kinds of experimental results confirm that BETAB nanocrystals can effectively reduce the defect density of perovskite films. Impressively, the resulting FA1-xMAxPbI3 based planar devices exhibit a champion power conversion efficiency (PCE) of 23.04% (certified: 22.10%) with a voltage loss of only 390 mV. Besides, the BETAB nanocrystals could simultaneously increase the hydrophobic property of perovskite films and prevent the reaction and formation of 2D perovskites during device operation. Correspondingly, the resulted devices exhibit excellent stability under moisture, heating, and operational tracking conditions.

During the past decade, metal halide perovskites are widely studied in the field of optoelectronic materials due to their unique optical and electrical properties. Lead-based halide perovskite solar cells (PSCs), in particular, currently achieve a record efficiency of 25.5%, thus showing strong potential in industrial application. However, toxicity of lead-based perovskite materials possesses great concerns to natural environment and human body. Therefore, the quest for nontoxic and eco-friendly elements to replace lead in perovskites is of great interest. Among all the element choices, tin(II) (Sn2+) is the most promising candidate. As a rising star of lead-free PSCs, Sn-based PSCs have drawn much attention and made promising progress during the past few years. While the rapid oxidation and decomposition of Sn-based perovskites result in poor stability and low efficiency of PSCs. In this review, structural, optoelectronic properties and the critical issues of Sn-based perovskite materials are analyzed. Then, a detailed discussion on the recent methods in solving critical issues of Sn-based perovskite devices, from optimization on materials physics to device performance, is also presented. Finally, remaining challenges and future perspective are given to advance the progression of Sn-based PSCs. Funding Agencies|National Key R&D Program of China [2017YFA0207400]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [62004027]; Special Program for Sichuan Youth Science and Technology Innovation Research Team [2019JDTD0006]; Anshan Hifichem Co. Ltd.

We report a facile and low-temperature aqueous route for the fabrication of various oxide thin films (Al 2 O 3 , In 2 O 3 and InZnO). A detail study is carried out to reveal the formation and properties of these sol-gel-derived thin films. The results show that the water-based oxide thin films undergo the decomposition of nitrate group as well as conversion of metal hydroxides to form metal oxide framework. High quality oxide thin film could be achieved at low temperature by this aqueous route. Furthermore, these oxide thin films are integrated to form thin-film transistors (TFTs) and the electrical performance is systematically studied. In particular, we successfully demonstrate In 2 O 3 /Al 2 O 3 TFTs with high mobility of 30.88 cm 2 V −1 s −1 and low operation voltage of 4 V at a maximum processing temperature of 250 °C.

MAPbI 3 perovskite is an important component for high-performance perovskite solar cell (PSC) but its own thin film stability is challenging in PSC community. Herein, we report a high crystallinity perovskite MAPbI 3 with texture structure prepared from HPbI 3 reacted with low partial pressure (LPP) MA gas, that has substantially higher both thermal and moisture stability than polycrystalline perovskite (PP) prepared from MAI+PbI 2 . A prototype reactor is developed to perform coordination engineering between MA vapor and HPbI 3 solid and facilitate the large-scale fabrication. The large Pb-N binding energy (~80.04 kJ mol −1 ) results in the liquefied state after MA adhesion. Finally, a high texture perovskite (TP) is formed after excess MA expeditious releasing. The MA-rich passivation through Pb-N bonding at interface and boundary contributes to the substantial improved stability. Besides, MA-rich species trigger an anti-degradation reaction in presence of moisture and thus endow stability above two months under ~65% humidity. The textured PSCs (TPSCs) deliver power conversion efficiency (PCE) between 15.5% and champion 18.9% in the batch deposition. Therefore, the coordination engineering improves the efficiency, stability, scalability and ease of fabrication together.

Droplet microfluidics is an emerging tool in many biological and chemical application areas such as digital polymerase chain reaction (PCR) and in vitro diagnosis because of its extremely small sample volume and wide range of possibilities for on-demand adjustment of droplet properties. Although centrifugal microfluidics has been reported as a viable scheme for droplet generation, there is not much progress as far as droplet manipulation and droplet-based reactions are concerned. In this paper, we report a microfluidic pressure regulator scheme along with the use of microcapillaries for periodic droplet generation and the subsequent fusion. This scheme enables fine control over droplet generation and the fusion process by varying the rotational frequency. To control the solution concentration in droplets, we have implemented several fusion devices, including one-to-one mode using a symmetric structure and ratio-adjustable mode with an asymmetric structure. As an application example, we performed cell transfection using the reported droplet-based technique, which resulted in considerable improvement in terms of transfection efficiency compared to the traditional bulk approach. In another example, we synthesized quasi-2D perovskites with controllable compositions and tunable photoluminescence peaks, thus confirming the volumetric accuracy of this approach down to the nano-liter scale. Compared to the common pressure pulsation approach, our centrifugal force actuation scheme offers the advantages of compactness and highly parallel batch processing. We anticipate that the new scheme will find many applications in cell biology and chemical synthesis.

Defects engineering can broaden the absorption band of wide band gap van der Waals (vdW) materials to the visible or near-IR regime at the expense of material stability and photoresponse speed. Herein, we introduce an atomic intercalation method that brings the wide band gap vdW α-MoO3 for vis–MIR broadband optoelectronic conversion. We confirm experimentally that intercalation significantly enhances photoabsorption and electrical conductivity buts effects negligible change to the lattice structure as compared with ion intercalation. Charge transfer from the Sn atom to the lattices induces an optoelectrical change. As a result, the Sn-intercalated α-MoO3 shows room temperature, air stable, broadband photodetection ability from 405 nm to 10 μm, with photoresponsivity better than 9.0 A W–1 in 405–1500 nm, ∼0.4 A W–1 at 3700 nm, and 0.16 A W–1 at 10 μm, response time of ∼0.1 s, and peak D* of 7.3 × 107 cm Hz0.5 W–1 at 520 nm. We further reveal that photothermal effect dominates in our detection range by real...

Dimension regulation and defect passivation are two key strategies for highly efficient and stable perovskite solar cell. Vapor deposition of perovskite is a toxic-solvent-free method for large-scale fabrication. However, without the assistance of solvent for crystal optimization, effective structural regulation and defect passivation become challenging. Here, detailed investigations on the structural evolution of perovskite thin film are carried out in sequential vapor deposition using mixed-vapor (R-NH3I/MAI). Correlation between electron donating ability of R-NH3I (BAI, PEAI, PMAI and ALI) molecule and the way of structural transition is established. It is found that R-NH3I with stronger electron-donating ability promoted the phase transition from three-dimensional (3D) to two-dimensional (2D) perovskite. Typically, the n value from 1 to 5 can be tuned by reaction time or component control using BAI with the strongest electron donating ability. R-NH3I with weak electron-donating ability suppresses the 3D to 2D transition, but enhances the defect passivation effect. The ALI with the weakest electron donating ability shows the best passivation effect, leading to the best device performance than that of the control 3D device, with PCE of 18.23% (0.045 cm2) and 15.48% (1 cm2) and the significantly improved stability. This study provides the evidence that the concept of Lewis acid-base reaction is applicable in vapor deposition, which provides us with the selection guide of R-NH3I molecules for structural design in vapor fabrication of perovskite thin film.

Quantification of intergrain length scale properties of CH3NH3PbI3 (MAPbI3) can provide further understanding of material physics, leading to improved device performance. In this work, we noticed that two typical types of facets appear in sequential deposited perovskite (SDP) films: smooth and steplike morphologies. By mapping the surface potential as well as the photoluminescence (PL) peak position, we revealed the heterogeneity of SDP thin films that smooth facets are almost intrinsic with a PL peak at 775 nm, while the steplike facets are p-type-doped with 5-nm blue-shifted PL peak. Considering the reaction process, we propose that the smooth facets have well-defined crystal lattices that resulted from the interfacial reaction between MAI and PbI2 domains containing low trap states density. The steplike facets are MAI-rich originated from the grain boundaries of PbI2 film and own more trap states. Conversion of steplike facets to smooth facets can be controlled by increasing the reaction time through O...

Trap states in semiconductors usually degrade charge separation and collection in photovoltaics due to trap-mediated nonradiative recombination. Here, it is found that perovskite can be heavily doped in low concentration with non-ignorable broadband infrared absorption in thick films and their trap states accumulate electrons through infrared excitation and hot carrier cooling. A hybrid one-sided abrupt perovskite/TiO2 p-N heterojunction is demonstrated that enables partial collection of these trap-filled charges through a tunneling process instead of detrimental recombination. The tunneling is from broadband trap states in the wide depleted p-type perovskite, across the barrier of the narrow depleted TiO2 region (

In this paper, the changes in solid-phase carbon structure and the formation of carbon nanotubes in the process of K-catalyzed pyrolysis of bituminous coal were investigated. The results showed that the content of carbon nanotubes in K-catalyzed coal pyrolysis products increased with the extension of residence time. When the residence times were 0, 30 and 90 min, the yields of carbon nanotubes in the coal pyrolysis products were 1.98 wt%, 6.85 wt% and 10.16 wt%, respectively. It was found that the aromatic carbon C C, C H and ether carbon C-O-C structures in coal were the main carbon sources for the growth of carbon nanotubes. The probable growth mechanism of carbon nanotubes in the process of K-catalyzed coal pyrolysis was proposed to be as follows: aromatic C C and C H structures in coal convert K components such as K2CO3 and K2O into metal K, and then metal K converts carbon atoms in the ether bond C-O-C structure into carbon atoms or clusters, which generate carbon nanotubes under the action of Fe catalyst particles in coal. This method provides a new strategy for the simultaneous high-value utilization of coal resources and macroscopic, low-cost preparation of carbon nanotubes.

Carbon nanotubes (CNTs) and activated carbon (AC) hybrids were obtained by co-pyrolysis of potassium hydroxide and bituminous coal. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman spectroscopy, X-ray Diffraction (XRD), and nitrogen adsorption measurements were used to investigate the characteristics of the samples and the effects of the final pyrolysis temperature and time on the structure of the carbon materials. The results indicated that the optimal range for the pyrolysis temperature and time for CNT growth were 900–950 °C and 45–90 min, respectively. The diameters of the as-prepared CNTs were in the range of 50–250 nm and their lengths were ∼15 μm. During the pyrolysis process, potassium hydroxide not only acted as the catalytic precursor to catalyze the CNT growth but also reacted with carbon to produce abundant micropores. Furthermore, the content of CNTs in the product after demineralization was significantly reduced. It was further confirmed by Inductively Coupled Plasma (ICP) analysis that the content of Fe, Co, and Ni decreased after demineralization, indicating that minerals in coal play an important role in the growth of coal-based CNTs.

Directional optical nanoantennas are often realized by nanostructured systems with ingenious or complex designs. Herein we report on the realization of directional scattering of visible light from a simple configuration made of single Ag nanorods supported on Si substrates, where the incident light can be routed toward the two flanks of each nanorod. Such an intriguing far-field scattering behavior, which has not been investigated so far, is proved to result from the near-field coupling between high-aspect-ratio Ag nanorods and high-refractive-index Si substrates. A simple and intuitive model is proposed, where the complicated plasmon resonance is found to be equivalent to several vertically aligned electric dipoles oscillating in phase, to understand the far-field properties of the system. The interference among the electric dipoles results in wavefront reshaping and sidewise light routing in a similar manner to the broadside antenna described in the traditional antenna theory, allowing for the naming of these Si-supported Ag nanorods as "broadside nanoantennas". We have carried out comprehensive experiments to understand the physical origins behind and the affecting factors on the directional scattering behavior of such broadside nanoantennas.

High quality polycrystalline CH3NH3PbI3 was prepared by dripping the γ-butyrolactone (GBL) solution of CH3NH3PbI3 into toluene, dimethylformamide (DMF) and dimethylsilicone oil. In toluene, a compact CH3NH3PbI3 thin film was observed but with grain size smaller than 1 μm because of the rapid extraction of GBL. As CH3NH3PbI3 is soluble in DMF, the crystallization in DMF is understood by interdiffusion induced local and temporal supersaturated droplets, which allow for growth of irregular, separated single crystals with size of more than 0.1 mm. In dimethylsilicone oil, compact, yolk-like polycrystalline CH3NH3PbI3 was observed. Unlike the round grains observed in toluene, it is composed of single crystal grains with clear angular surfaces. The average crystal size is tens of μm and can be modulated by the solvent temperature. We suggest that the poor miscibility between GBL and dimethylsilicone oil, and the poor solubility of CH3NH3I, PbI2 and CH3NH3PbI3 in the dimethylsilicone oil, allow slow extraction of GBL while keeping the stoichiometry of CH3NH3PbI3. The results offer a feasible and high-yielding method for growing uniform CH3NH3PbI3 crystals in a few seconds.

The precursor of solution-processed perovskite thin films is one of the most central components for high-efficiency perovskite solar cells. We first present the crucial colloidal chemistry visualization of the perovskite precursor solution based on analytical spectra and reveal that perovskite precursor solutions for solar cells are generally colloidal dispersions in a mother solution, with a colloidal size up to the mesoscale, rather than real solutions. The colloid is made of a soft coordination complex in the form of a lead polyhalide framework between organic and inorganic components and can be structurally tuned by the coordination degree, thereby primarily determining the basic film coverage and morphology of deposited thin films. By utilizing coordination engineering, particularly through employing additional methylammonium halide over the stoichiometric ratio for tuning the coordination degree and mode in the initial colloidal solution, along with a thermal leaching for the selective release of excess methylammonium halides, we achieved full and even coverage, the preferential orientation, and high purity of planar perovskite thin films. We have also identified that excess organic component can reduce the colloidal size of and tune the morphology of the coordination framework in relation to final perovskite grains and partial chlorine substitution can accelerate the crystalline nucleation process of perovskite. This work demonstrates the important fundamental chemistry of perovskite precursors and provides genuine guidelines for accurately controlling the high quality of hybrid perovskite thin films without any impurity, thereby delivering efficient planar perovskite solar cells with a power conversion efficiency as high as 17% without distinct hysteresis owing to the high quality of perovskite thin films.

The mixed cation lead mixed halide perovskite (MLMP) Csx FA1-x PbIy Br3-y is one of the most promising candidates for both single-junction and tandem solar cells due to its high efficiency and remarkable stability. However, the composition effect on thermal stability and photovoltaic performances has not yet been comprehensively investigated. Therefore, the interplay between composition, crystal structure, morphology, and optoelectronic properties under heat stress, is systematically elucidated here through a series of in situ characterizations. It is revealed for the first time that the FA+ and Br- release synchronously at first even under mild annealing. This leads to a serious FA- and Br-deficiency issue, with only 88.3% of Br and 90.2% of FA retained after annealing at 100 °C, which significantly magnifies the hysteresis, phase segregation, and instability issues. Finally, a trace amount of FA+ and Br- is introduced onto the post-annealed MLMP surface to compensate for the deficiency through vacancy filling. The degradation lifetime to 80% of the initial efficiency (t80 ) is improved from 504 to 1056 h and the hysteresis issue is also well resolved. This work highlights the importance of the synergetic composition effect of the organic cation and halide anion on stability and efficiency optimization for long-term applications.

Perovskite solar cells have received worldwide interests due to swiftly improved efficiency but the poor stability of the perovskite component hampers the device fabrication under normal condition. Herein, we develop a reliable nonstoichiometric acid–base reaction route to stable perovskite films by intermediate chemistry and technology. Perovskite thin-film prepared by nonstoichiometric acid–base reaction route is stable for two months with negligible PbI2-impurity under ∼65% humidity, whereas other perovskites prepared by traditional methods degrade distinctly after 2 weeks. Route optimization involves the reaction of PbI2 with excess HI to generate HPbI3, which subsequently undergoes reaction with excess CH3NH2 to deliver CH3NH3PbI3 thin films. High quality of intermediate HPbI3 and CH3NH2 abundance are two important factors to stable CH3NH3PbI3 perovskite. Excess volatile acid/base not only affords full conversion in nonstoichiometric acid–base reaction route but also permits its facile removal for stoichiometric purification, resulting in average efficiency of 16.1% in forward/reverse scans., The stability of perovskite thin films and devices depends on a number of environmental factors, amongst which humidity. Here, Long et al. develop a synthetic route using a nonstoichiometric acid-base reaction to prepare films stable in humid environments for two months.

We developed a molecule/polymer composite hole transporting material (HTM) with a periodic microstructure for morphology replication of a corrugated Au electrode, which in combination plays a dual role in the optical and electronic enhancement of high performance perovskite solar cells (PSCs). The electro-optics revealed that perovskite couldn't readily extinct the red light even though the thickness increased to 370 nm, but we found that the quasi periodic microstructure composite (PMC) HTM in combination with the conformal Au electrode could promote the absorption through the enhanced cavity effects, leading to comparable absorption even using much thinner perovskite (240 nm). We identified that the cavity was the combination of Fabry-Pérot interferometer and surface plasmonic resonance, with light harvesting enhancement through surface plasmon polariton or waveguide modes that propagate in the plane of the perovskite layer. On the other hand, the PMC HTM increased hole conductivity by one order of magnitude with respect to standard spiro-OMeTAD HTM due to molecular packing and self-assembly, embodying traceable hole mobility and density elevation up to 3 times, and thus the hysteresis was greatly avoided. Owing to dual optical and electronic enhancement, the PMC PSC afforded high efficiency PSC using as thin as 240 nm perovskite layer, delivering a V(oc) of 1.05 V, J(sc) of 22.9 mA cm(-2), FF of 0.736, and efficiency amounting to 17.7% PCE, the highest efficiency with ultrathin perovskite layer.

The mixed perovskite (FAPbI3)1−x(MAPbBr3)x, prepared by directly mixing different perovskite components, suffers from phase competition and a low-crystallinity character, resulting in instability, despite the high efficiency. In this study, a dual ion exchange (DIE) method is developed by treating as-prepared FAPbI3 with methylammonium brodide (MABr)/tert-butanol solution. The converted perovskite thin film shows an optimized absorption edge at 800 nm after reaction time control, and the high crystallinity can be preserved after MABr incorporation. More importantly, it is found that the threshold electrical field to initiate ion migration is greatly increased in DIE perovskite thin film because excess MABr on the surface can effectively heal structural defects located on grain boundaries during the ion exchange process. It contributes to the over-one-month moisture stability under ≈65% room humidity (RH) and greatly enhanced light stability for the bare perovskite film. As a result of preserved high crystallinity and simultaneous grain boundary passivation, the perovskite solar cells fabricated by the DIE method demonstrate reliable reproducibility with an average power conversion efficiency (PCE) of 17% and a maximum PCE of 18.1%, with negligible hysteresis.