首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
To alleviate photoinduced charge recombination in semiconducting nanomaterials represents an important endeavor toward high‐efficiency photocatalysis. Here a judicious integration of piezoelectric and photocatalytic properties of organolead halide perovskite CH3NH3PbI3 (MAPbI3) to enable a piezophotocatalytic activity under simultaneous ultrasonication and visible light illumination for markedly enhanced photocatalytic hydrogen generation of MAPbI3 is reported. The conduction band minimum of MAPbI3 is higher than hydrogen generation potential (0.046 V vs normal hydrogen electrode), thereby rendering efficient hydrogen evolution. In addition, the noncentrosymmetric crystal structure of MAPbI3 enables its piezoelectric properties. Thus, MAPbI3 readily responds to external mechanical force, creating a built‐in electric field for collective piezophotocatalysis as a result of effective separation of photogenerated charge carriers. The experimental results show that MAPbI3 powders exhibit superior piezophotocatalytic hydrogen generation rate (23.30 µmol h?1) in hydroiodic acid (HI) solution upon concurrent light and mechanical stimulations, much higher than that of piezocatalytic (i.e., 2.21 µmol h?1) and photocatalytic (i.e., 3.42 µmol h?1) hydrogen evolution rate as well as their sum (i.e., 5.63 µmol h?1). The piezophotocatalytic strategy provides a new way to control the recombination of photoinduced charge carriers by cooperatively capitalizing on piezocatalysis and photocatalysis of organolead halide perovskites to yield highly efficient piezophotocatalysis.  相似文献   

2.
Despite their excellent power conversion efficiency, MAPbI3 solar cells exhibit strong hysteresis that hinders reliable device operation. Herein it is shown that ionic motion is the dominant mechanism underlying hysteresis of MAPbI3 solar cells by studying the effects of electrical poling in different temperature ranges. Complete suppression of the hysteresis below 170 K is consistent with temperature activated diffusion of I? anions and/or the motion of the MA+ cations. Ionic motion has important effect on the overall efficiency of the MAPbI3 solar cells: the initial decrease of the power conversion efficiency while lowering the operating temperature is recovered and even enhanced up to 20% of its original value by applying an electrical poling. The open circuit voltage significantly increases and the current density fully recovers due to the reduction of the electron extraction barrier at the TiO2/MAPbI3 interface driven by the charge accumulation at the interface. Moreover, beside TiO2/MAPbI3 interfacial charge transfer, charge transport in TiO2 strongly affects the photovoltaic performance, as revealed by MAPbI3/ms‐TiO2 field effect transistors. These results establish the basis to develop effective strategies to mitigate operational instability of perovskites solar cells.  相似文献   

3.
Charge‐carriers photoexcited above a semiconductor's bandgap rapidly thermalize to the band‐edge. The cooling of these difficult to collect “hot” carriers caps the available photon energy that solar cells–including efficient perovskite solar cells–may utilize. Here, the dynamics and efficiency of hot carrier extraction from MAPbI3 (MA = methylammonium) perovskite by spiro‐OMeTAD (a hole‐transporting layer) and TiO2 (an electron‐transporting layer) are investigated and explained using both ultrafast electronic spectroscopy and theoretical modeling. Time‐resolved spectroscopy reveals a quasi‐equilibrium distribution of hot carriers forming upon excess‐energy excitation of the perovskite–a distribution largely unaffected by the presence of TiO2. In contrast, the quasi‐equilibrium distribution of hot carriers is virtually nonexistent when spiro‐OMeTAD is present, which is indicative of efficient hot hole extraction at the interface of MAPbI3. Density functional theory calculations predict that deep energy‐levels of MAPbI3 exhibit electronically delocalized character, with significant overlap with the localized valence band charge of the spiro‐OMeTAD molecules lying on the surface of MAPbI3. Consequently, hot holes are easily extracted from the deep energy‐levels of MAPbI3 by spiro‐OMeTAD. These findings uncover the origins of efficient hot hole extraction in perovskites and offer a practical blueprint for optimizing solar cell interlayers to enable hot carrier utilization.  相似文献   

4.
Hybrid lead halide perovskites have reached very large solar to electricity power conversion efficiencies, in some cases exceeding 20%. The most extensively used perovskite‐based solar cell configuration comprises CH3NH3PbI3 (MAPbI3) in combination with electron (TiO2) and hole 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9‐spiro‐bifluorene (spiro‐OMeTAD) selective contacts. The recognition that the solar cell performance is heavily affected by time scale of the measurement and preconditioning procedures has raised many concerns about the stability of the device and reliability for long‐time operation. Mechanisms at contacts originate observable current–voltage distortions. Two types of reactivity sources have been identified here: (i) weak Ti–I–Pb bonds that facilitate interfacial accommodation of moving iodine ions. This interaction produces a highly reversible capacitive current originated at the TiO2/MAPbI3 interface, and it does not alter steady‐state photovoltaic features. (ii) An irreversible redox peak only observable after positive poling at slow scan rates. It corresponds to the chemical reaction between spiro‐OMeTAD+ and migrating I? which progressively reduces the hole transporting material conductivity and deteriorates solar cell performance.  相似文献   

5.
This study describes the relationships between dinitrogen (N2) fixation, dihydrogen (H2) production, and electron transport associated with photosynthesis and respiration in the marine cyanobacterium Trichodesmium erythraeum Ehrenb. strain IMS101. The ratio of H2 produced:N2 fixed (H2:N2) was controlled by the light intensity and by the light spectral composition and was affected by the growth irradiance level. For Trichodesmium cells grown at 50 μmol photons · m?2 · s?1, the rate of N2 fixation, as measured by acetylene reduction, saturated at light intensities of 200 μmol photons · m?2 · s?1. In contrast, net H2 production continued to increase with light levels up to 1,000 μmol photons · m?2 · s?1. The H2:N2 ratios increased monotonically with irradiance, and the variable fluorescence measured using a fast repetition rate fluorometer (FRRF) revealed that this increase was accompanied by a progressive reduction of the plastoquinone (PQ) pool. Additions of 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐p‐benzoquinone (DBMIB), an inhibitor of electron transport from PQ pool to PSI, diminished both N2 fixation and net H2 production, while the H2:N2 ratio increased with increasing level of PQ pool reduction. In the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), nitrogenase activity declined but could be prolonged by increasing the light intensity and by removing the oxygen supply. These results on the coupling of N2 fixation and H2 cycling in Trichodesmium indicate how light intensity and light spectral quality of the open ocean can influence the H2:N2 ratio and modulate net H2 production.  相似文献   

6.
Photocatalytic reduction of CO2 with H2O vapor is gaining increased interest because it is a promising “green chemistry” route for the direct conversion of CO2 to value‐added chemicals driven by solar energy. To increase the efficiency of photocatalytic conversion, most efforts are made by exploring various photocatalysts while little effort on advanced light management. For the first time, it is demonstrated that bio‐degradable transparent paper with excellent light diffusivity can effectively enhance the light utilization of photocatalytic reactions when attached on the device surface, and thus greatly increase the conversion efficiency. As a proof‐of‐concept, a graphitic carbon nitride (g‐C3N4) photocatalyst with transparent paper attached, exhibited 1.5 times higher photocatalytic activity than bare g‐C3N4 in the reduction of CO2 under visible light irradiation. The improved catalytic performance can be ascribed to the (1) refractive index matching and (2) enhanced light absorption via prolonged light traveling path in transparent paper, which decreases the light reflection at surface and traps the absorbed light inside, leading to an increased light absorption at the active layer of the device. The transparent paper with a controllable light management behavior has an unprecedented potential for applications in photocatalysis as a general method for improved light utilization.  相似文献   

7.
Remarkable power conversion efficiencies (PCE) of metal–halide perovskite solar cells (PSCs) are overshadowed by concerns about their ultimate stability, which is arguably the prime obstacle to commercialization of this promising technology. Herein, the problem is addressed by introducing ethane‐1,2‐diammonium (+NH3(CH2)2NH3+, EDA2+) cations into the methyl ammonium (CH3NH3+, MA+) lead iodide perovskite, which enables, inter alia, systematic tuning of the morphology, electronic structure, light absorption, and photoluminescence properties of the perovskite films. Incorporation of <5 mol% EDA2+ induces strain in the perovskite crystal structure with no new phase formed. With 0.8 mol% EDA2+, PCE of the MAPbI3‐based PSCs (aperture of 0.16 cm2) improves from 16.7% ± 0.6% to 17.9% ± 0.4% under 1 sun irradiation, and fabrication of larger area devices (aperture 1.04 cm2) with a certified PCE of 15.2% ± 0.5% is demonstrated. Most importantly, EDA2+/MA+‐based solar cells retain 75% of the initial performance after 72 h of continuous operation at 50% relative humidity and 50 °C under 1 sun illumination, whereas the MAPbI3 devices degrade by approximately 90% within only 15 h. This substantial improvement in stability is attributed to the steric and coulombic interactions of embedded EDA2+ in the perovskite structure.  相似文献   

8.
As perovskite solar cells (PSCs) are highly efficient, demonstration of high‐performance printed devices becomes important. 2D/3D heterostructures have recently emerged as an attractive way to relieving the film inhomogeneity and instability in perovskite devices. In this work, a 2D/3D ensemble with 2D perovskites self‐assembled atop 3D methylammonium lead triiodide (MAPbI3) via a one‐step printing process is shown. A clean and flat interface is observed in the 2D/3D bilayer heterostructure for the first time. The 2D perovskite capping layer significantly suppresses nonradiative charge recombination, resulting in a marked increase in open‐circuit voltage (VOC) of the devices by up to 100 mV. An ultrahigh VOC of 1.20 V is achieved for MAPbI3 PSCs, corresponding to 91% of the Shockley–Queisser limit. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of the 2D perovskites. These results suggest a viable approach for scalable fabrication of highly efficient perovskite solar cells with enhanced environmental stability.  相似文献   

9.
This paper presents a systematic study of the influence of electron‐transport materials on the operation stability of the inverted perovskite solar cells under both laboratory indoor and the natural outdoor conditions in the Negev desert. It is shown that all devices incorporating a Phenyl C61 Butyric Acid Methyl ester ([60]PCBM) layer undergo rapid degradation under illumination without exposure to oxygen and moisture. Time‐of‐flight secondary ion mass spectrometry depth profiling reveals that volatile products from the decomposition of methylammonium lead iodide (MAPbI3) films diffuse through the [60]PCBM layer, go all the way toward the top metal electrode, and induce its severe corrosion with the formation of an interfacial AgI layer. On the contrary, alternative electron‐transport material based on the perylendiimide derivative provides good isolation for the MAPbI3 films preventing their decomposition and resulting in significantly improved device operation stability. The obtained results strongly suggest that the current approach to design inverted perovskite solar cells should evolve with respect to the replacement of the commonly used fullerene‐based electron‐transport layers with other types of materials (e.g., functionalized perylene diimides). It is believed that these findings pave a way toward substantial improvements in the stability of the perovskite solar cells, which are essential for successful commercialization of this photovoltaic technology.  相似文献   

10.
A rapid layer‐specific annealing on perovskite active layer enabled by ultraviolet (UV) light‐emitting diode (LED) is demonstrated and efficiency close to 19% is achieved in a simple planar inverted structure ITO/PEDOT:PSS/MAPbI3/PC71BM/Al without any device engineering. These results demonstrate that if the UV dosage is well managed, UV light is capable of annealing perovskite into high‐quality film rather than simply damaging it. Different in principle from other photonic treatment techniques that can heat up and damage underlying films, the UV‐LED‐annealing method enables layer‐specific annealing because LED light source is able to provide a specific UV wavelength for maximum light absorption of target film. Moreover, the layer‐specific photonic treatment allows accurate estimation of the crystallization energy required to form perovskite film at device quality level.  相似文献   

11.
The photocatalytic reduction of nitrogen (N2) with water (H2O) as the reducing agent holds great promise as a sustainable future technology for the synthesis of ammonia (NH3). Herein, the effect of oxygen vacancies and electron‐rich Cuδ+ on the performance of zinc‐aluminium layered double hydroxide (ZnAl‐LDH) nanosheet photocatalysts for N2 reduction to NH3 under UV–vis excitation is systematically explored. Results show that a 0.5%‐ZnAl‐LDH nanosheet photocatalyst (containing 0.5 mol% Cu by metal basis) affords a remarkable NH3 production rate of 110 µmol g?1 h?1 and excellent stability in pure water. The X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu addition imparts oxygen vacancies and coordinatively unsaturated Cuδ+ (δ < 2) with electron‐rich property in the ZnAl‐LDH nanosheets, both of which readily contribute to efficient separation and transfer of photogenerated electrons and holes and promote N2 adsorption, thereby both activating N2 and facilitating its multielectrons reduction to NH3.  相似文献   

12.
Photoautotrophic growth of a marine non-heterocystous filamentous cyanobacterium, Symploca sp. strain S84, was examined under nitrate-assimilating and N2-fixing conditions. Under continuous light, photon flux density of 55 μmol photons·m−2 ·s−1 was at a saturating level for growth, and light did not inhibit the growth rate under N2-fixing conditions even when the photon flux density was doubled (110 μmol photons·m−2 ·s−1). Doubling times of the N2-fixing cultures under 55 and 110 μmol photons·m−2 ·s−1 were about 30 and 31 h, respectively. Under 110 μmol photons·m−2 ·s−1 during the light phase of an alternating 12:12-h light:dark (L:D) cycle, the doubling time of the N2-fixing culture was also about 30 h. When grown diazotrophically under a 12:12-h L:D regime, C2H2 reduction activity was observed mainly during darkness. In continuous light, relatively large cyclic fluctuations in C2H2 reduction were observed during growth. The short-term (<4 h) effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; 5 μM) indicated that C2H2 reduction activity was not influenced by photosynthetic O2 evolution. Long-term (24 h) effects of DCMU indicated that photosynthesis and C2H2 reduction activity occur simultaneously. These results indicate that strain S84 grows well under diazotrophic conditions when saturating light is supplied either continuously or under a 12:12-h L:D diel light regime.  相似文献   

13.
Here for the first time the design and optimization are presented of a three‐component Au/TiO2–gC3N4 nanocomposite photocatalyst able to efficiently produce H2 from water using very low amounts of sacrificial agents and under visible light irradiation. This enhanced photocatalytic behavior compared to Au/TiO2 and Au/gC3N4 materials is the result of synergetic effects due to high quality assembly and interface between the three components. This optimized nanoscale assembly characterized by simultaneous favorable nanoheterojunction formation between g‐C3N4 and TiO2 semiconductors, as well as AuNPs/gC3N4 and AuNPs/TiO2 junctions, leads to enhanced visible light harvesting, charge separation, and H2 production. This composite photocatalyst yields a high H2 production (350 µmol?1 h?1 gcatalyst?1) under visible light irradiation with minimal amounts of sacrificial agent (≤1 vol%), corresponding to activities much higher than reported so far under comparable conditions.  相似文献   

14.
Methylammonium lead iodide (MAPbI3) perovskites are organic–inorganic semiconductors with long carrier diffusion lengths serving as the light‐harvesting component in optoelectronics. Through a substitutional growth of MAPbI3 catalyzed by polar protic alcohols, evidence is shown for their substrate‐ and annealing‐free production and use of toxic solvents and high temperature is prevented. The resulting variable‐sized crystals (≈100 nm–10 µm) are found to be tetragonally single‐phased in alcohols and precipitated as powders that are metallic‐lead‐free. A comparatively low MAPbI3 yield in toluene supports the role of alcohol polarity and the type of solvent (protic vs aprotic). The theoretical calculations suggest that overall Gibbs free energy in alcohols is lowered due to their catalytic impact. Based on this alcohol‐catalyzed approach, MAPbI3 is obtained, which is chemically stable in air up to ≈1.5 months and thermally stable (≤300 °C). This method is amendable to large‐scale manufacturing and ultimately can lead to energy‐efficient, low‐cost, and stable devices.  相似文献   

15.
Grains and grain boundaries play key roles in determining halide perovskite‐based optoelectronic device performance. Halide perovskite monocrystalline solids with large grains, smaller grain boundaries, and uniform surface morphology improve charge transfer and collection, suppress recombination loss, and thus are highly favorable for developing efficient solar cells. To date, strategies of synthesizing high‐quality thin monocrystals (TMCs) for solar cell applications are still limited. Here, by combining the antisolvent vapor‐assisted crystallization and space‐confinement strategies, high‐quality millimeter sized TMCs of methylammonium lead iodide (MAPbI3) perovskites with controlled thickness from tens of nanometers to several micrometers have been fabricated. The solar cells based on these MAPbI3 TMCs show power conversion efficiency (PCE) of 20.1% which is significantly improved compared to their polycrystalline counterparts (PCE) of 17.3%. The MAPbI3 TMCs show large grain size, uniform surface morphology, high hole mobility (up to 142 cm2 V?1 s?1), as well as low trap (defect) densities. These properties suggest that TMCs can effectively suppress the radiative and nonradiative recombination loss, thus provide a promising way for maximizing the efficiency of perovskite solar cells.  相似文献   

16.
Lead tri‐iodide methylammonium (MAPbI3) perovskite polycrystalline materials show complex optoelectronic behavior, largely because their 3D semiconducting inorganic framework is strongly perturbed by the organic cations and ubiquitous structural or chemical inhomogeneities. Here, a newly developed time‐dependent density functional theory‐based theoretical formalism is taken advantage of. It treats electron–hole and electron–nuclei interactions on the same footing to assess the many‐body excited states of MAPbI3 perovskites in their pristine state and in the presence of point chemical defects. It is shown that lead and iodine vacancies yield deep trap states that can be healed by dynamic effects, namely rotation of the methylammonium cations in response to point charges, or through slight changes in chemical composition, namely by introducing a tiny amount of chlorine dopants in the defective MAPbI3. The theoretical results are supported by photoluminescence experiments on MAPbI3?mClm and pave the way toward the design of defect‐free perovskite materials with optoelectronic performance approaching the theoretical limits.  相似文献   

17.
Green plants use solar energy efficiently in nature. Simulating the exquisite structure of a natural photosynthesis system may open a new approach for the construction of desirable photocatalysts with high light harvesting efficiency and performance. Herein, inspired by the excellent light utilization of “leaf mosaic” in plants, a novel vine‐like g‐C3N4 (V‐CN) is synthesized for the first time by copolymerizing urea with dicyandiamide‐formaldehyde (DF) resin. The as‐prepared V‐CN exhibits ultrahigh photocatalytic hydrogen production of 13.6 mmol g?1 h?1 under visible light and an apparent quantum yield of 12.7% at 420 nm, which is ≈38 times higher than that of traditional g‐C3N4, representing one of the highest‐activity g‐C3N4‐based photocatalysts. This super photocatalytic performance is derived from the unique leaf mosaic structure of V‐CN, which effectively improves its light utilization and affords a larger specific surface area. In addition, the introduction of DF resin further optimizes the energy band of V‐CN, extends its light absorption, and improves its crystallinity and interfacial charge transport, resulting in high performance. It is an easy and green strategy for the preparation of broad‐spectrum, high‐performance g‐C3N4, which presents significant advancement for the design of other nanophotocatalysts by simulating the fine structure of natural photosynthesis.  相似文献   

18.
In p‐i‐n planar perovskite solar cells (pero‐SCs) based on methylammonium lead iodide (MAPbI3) perovskite, high‐quality MAPbI3 film, perfect interfacial band alignment and efficient charge extracting ability are critical for high photovoltaic performance. In this work, a hydrophilic fullerene derivative [6,6]‐phenyl‐C61‐butyric acid‐(3,4,5‐tris(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)phenyl)methanol ester (PCBB‐OEG) is introduced as additive in the methylammonium iodide precursor solution in the preparation of MAPbI3 perovskite film by two‐step sequential deposition method, and obtained a top‐down gradient distribution with an ultrathin top layer of PCBB‐OEG. Meanwhile, a high‐quality perovskite film with high crystallinity, less trap‐states, and dense‐grained uniform morphology can well grow on both hydrophilic (poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonic acid)) and hydrophobic (polytriarylamine, PTAA) hole transport layers. When the PCBB‐OEG‐containing perovskite film (pero‐0.1) is prepared in a p‐i‐n planar pero‐SC with the configuration of ITO/PTAA/pero‐0.1/[6,6]‐phenyl‐C61‐butyric acid methyl ester/Al, the device delivers a promising power conversion efficiency (PCE) of 20.2% without hysteresis, which is one of the few PCE over 20% for the p‐i‐n planar pero‐SCs. Importantly, the pero‐0.1‐based device shows an excellent stability that can retain 98.4% of its initial PCE after being exposed for 300 h under ambient atmosphere with a high humidity, and the flexible pero‐SCs based on pero‐0.1 also demonstrate a promising PCE of 18.1%.  相似文献   

19.
Recently, considerable progress is achieved in lab prototype perovskite solar cells (PSCs); however, the stability of outdoor applications of PSCs remains a challenge due to the high sensitivity of perovskite material under moist and ultraviolet (UV) light conditions. In this work, the UV photostability of PSC devices is improved by incorporating a photon downshifting layer—SrAl2O4: Eu2+, Dy3+ (SAED)—prepared using the pulsed laser deposition approach. Light‐induced deep trap states in the photoactive layer are depressed, and UV light‐induced device degradation is inhibited after the SAED modification. Optimized power conversion efficiency (PCE) of 17.8% is obtained through the enhanced light harvesting and reduced carrier recombination provided by SAED. More importantly, a solar energy storage effect due to the long‐persistent luminescence of SAED is obtained after light illumination is turned off. The introduction of downconverting material with long‐persistent luminescence in PSCs not only represents a new strategy to improve PCE and light stability by photoconversion from UV to visible light but also provides a new paradigm for solar energy storage.  相似文献   

20.
Nitrite (NO2) can accumulate during nitrification in soil following fertilizer application. While the role of NO2 as a substrate regulating nitrous oxide (N2O) production is recognized, kinetic data are not available that allow for estimating N2O production or soil‐to‐atmosphere fluxes as a function of NO2 levels under aerobic conditions. The current study investigated these kinetics as influenced by soil physical and biochemical factors in soils from cultivated and uncultivated fields in Minnesota, USA. A linear response of N2O production rate () to NO2 was observed at concentrations below 60 μg N g−1 soil in both nonsterile and sterilized soils. Rate coefficients (Kp) relating to NO2 varied over two orders of magnitude and were correlated with pH, total nitrogen, and soluble and total carbon (C). Total C explained 84% of the variance in Kp across all samples. Abiotic processes accounted for 31–75% of total N2O production. Biological reduction of NO2 was enhanced as oxygen (O2) levels were decreased from above ambient to 5%, consistent with nitrifier denitrification. In contrast, nitrate (NO3)‐reduction, and the reduction of N2O itself, were only stimulated at O2 levels below 5%. Greater temperature sensitivity was observed for biological compared with chemical N2O production. Steady‐state model simulations predict that NO2 levels often found after fertilizer applications have the potential to generate substantial N2O fluxes even at ambient O2. This potential derives in part from the production of N2O under conditions not favorable for N2O reduction, in contrast to N2O generated from NO3 reduction. These results have implications with regard to improved management to minimize agricultural N2O emissions and improved emissions assessments.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号