Adjusting energy level alignment between HTL and CsPbI_(2)Br to improve solar cell efficiency

Lead halide perovskites are at the forefront of optoelectronic materials due to their high absorption coefficient,tunable bandgap,long carrier diffusion length,and small exciton binding energy[1−3],yielding high-performance optoelectronic devices.

SiO2 nanoparticle-regulated crystallization of lead halide perovskite and improved efficiency of carbon-electrode-based low-temperature planar perovskite solar cells

SiO2 nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method,which was used in the low-temperature-processed,carbon-electrode-basing,hole-conductor-free planar perovskite solar cells.It was observed that,after adding small amount of SiO2 precursor(1 vol%)into the lead iodide solution,performance parameters of open-circuit voltage,short-circuit current and fill factor were all upgraded,which helped to increase the power conversion efficiency(reverse scan)from 11.44(±1.83)%(optimized at 12.42%)to 14.01(±2.14)%(optimized at 15.28%,AM 1.5G,100 mW/cm^2).Transient photocurrent decay curve measurements showed that,after the incorporation of SiO2 nanoparticles,charge extraction was accelerated,while transient photovoltage decay and dark current curve tests both showed that recombination was retarded.The improvement is due to the improved crystallinity of the perovskite film.X-ray diffraction and scanning electron microscopy studies observed that,with incorporation of amorphous SiO2 nanoparticles,smaller crystallites were obtained in lead iodide films,while larger crystallites were achieved in the final perovskite film.This study implies that amorphous SiO2 nanoparticles could regulate the coarsening process of the perovskite film,which provides an effective method in obtaining high quality perovskite film.

Interfaces between MoO x and Mo X2(X=S,Se,and Te)

In the past decades there have been many breakthroughs in low-dimensional materials,especially in two-dimensional(2D)atomically thin crystals like graphene.As structural analogues of graphene but with a sizeable band gap,monolayers of atomically thin transition metal dichalcogenides(with formula of MX2,M=Mo,W;X=S,Se,Te,etc.)have emerged as the ideal 2D prototypes for exploring fundamentals in physics such as valleytronics due to the quantum confinement effects,and for engineering a wide range of nanoelectronic,optoelectronic,and photocatalytic applications.Transition metal trioxides as promising materials with low evaporation temperature,high work function,and inertness to air have been widely used in the fabrication and modification of MX2.In this review,we reported the fabrications of one-dimensional MoS2 wrapped MoO2 single crystals with varied crystal direction via atmospheric pressure chemical vapor deposition method and of 2D MoOx covered MoX2 by means of exposing MoX2 to ultraviolet ozone.The prototype devices show good performances.The approaches are common to other transition metal dichalcogenides and transition metal oxides.

Stress compensation based on interfacial nanostructures for stable perovskite solar cells

The long-term stability issue of halide perovskite solar cells hinders their commercialization.The residual stress-strain affects device stability,which is derived from the mismatched thermophysical and mechanical properties between adjacent layers.In this work,we introduced the Rb_(2)CO_(3)layer at the interface of SnO_(2)/perovskite with the hierarchy morphology of snowflake-like microislands and dendritic nanostructures.With a suitable thermal expansion coefficient,the Rb_(2)CO_(3)layer benefits the interfacial stress relaxation and results in a compressive stress-strain in the perovskite layer.Moreover,reduced nonradiative recombination losses and optimized band alignment were achieved.An enhancement of open-circuit voltage from 1.087 to 1.153 V in the resultant device was witnessed,which led to power conversion efficiency(PCE)of 22.7%(active area of 0.08313 cm^(2))and 20.6%(1 cm2).Moreover,these devices retained 95%of its initial PCE under the maximum power point tracking(MPPT)after 2700 h.It suggests inorganic materials with high thermal expansion coefficients and specific nanostructures are promising candidates to optimize interfacial mechanics,which improves the operational stability of perovskite cells.

van der Waals epitaxial growth of ultrathin metallic NiSe nanosheets on WSe2 as high performance contacts for WSe2 transistors

A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts,which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process.Here,we report the in situ growth of ultrathin metallic NiSe single crystals on WSe2 in which the metallic NiSe nanosheets function as the contact electrodes to WSe2,creating an interface that is essentially free from chemical disorder.The NiSe/WSe2 heterostructures also exhibit well-aligned lattice orientation between the two layers,forming a periodic Moire pattern.Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature,as evidenced by the extra-high electrical conductivity of up to 1.6×10^6 S-nf1.The WSe2 transistors with the NiSe contact show field-effect mobilities (/vFe) more than double that with Cr/Au electrodes.This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials,and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides.

Distributed Energy Management of Integrated Electricity-thermal Systems for High-speed Railway Traction Grids and Stations

This paper proposes an integrated electricity-ther-mal energy management system(EMS)for high-speed railways.First,an operational model is built for the integrated electricity-thermal system,including a train operation EMS(TO-EMS)model and station operation EMS(SO-EMS)model.In the TO-EMS model,traction grids(TGs)are formulated with a solvable second-order cone programming problem.In the SO-EMS model,station indoor thermal systems are taken into account,and the building heat exchange process and solar radiation influence upon station indoor temperature are also included.Then the TO-EMS and the SO-EMS are coordinated with an alternating direction method of the multipliers-based(ADMM-based)algo-rithm,protecting the privacy and interests both for the train dispatch center and stations.To demonstrate the effectiveness of the proposed railway EMS,a modified realistic high-speed railway segment with six stations in North China with summer and winter scenarios is studied.

Coordinated Dispatch of Integrated Electricity-Natural Gas System and the Freight Railway Network

With the significant development of liquefied natural gas(LNG)rail transport,the railway system is increasingly more closely connected with the integrated electricity-natural gas system(IEGS).To coordinate the economic operations of the two systems,this paper innovatively proposes a coordinated dispatch model of IEGS with LNG infrastructures and a freight railway network with LNG transport.First,an operational scheduling model of the railway network,considering energy consumption,is put forward for both LNG transmission and ordinary freight transport.Then,the coordinated dispatch problem of IEGS and the railway network is formulated into a mixed-integer linear programming model via the big M method and a modified incremental linearization approach.Finally,a bi-level optimization algorithm based on generalized benders decomposition(GBD)is presented to solve the coordinated dispatch problem due to the restrictions on exchanging private information.Case studies demonstrate the effectiveness of the proposed model and algorithm as well as the potential benefit for wind power accommodation.

Enormous enhancement in electrical performance of few-layered MoTe2 due to Schottky barrier reduction induced by ultraviolet ozone treatment

Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically investigated a convenient and effective method,ultraviolet ozone treatment,for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance.The resulted hole concentration and mobility are near 100 times enhanced to be〜1.0×10^13 cm^-2 and 101.4 cm^2/(V·s),respectively,and the conductivity is improved by 5 orders of magnitude.These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature.Compared with the pristine one,the photoresponsivity(522 mA/W)is enhanced approximately 100 times.Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx(x<3),as proved by photoemission spectroscopy.Additionally,the p-doped devices exhibit excellent stability in ambient air.Our findings show significant potential in future nanoelectronic and optoelectronic applications.

Optimal scheduling of power systems considering demand response

A novel optimal scheduling method considering demand response is proposed for power systems incorporating with large scale wind power.The proposed method can jointly dispatch the energy resources and demand side resources to mitigate the fluctuation of load and wind power output.It is noticed in practical operation that,without customer’s satisfaction being considered,customers might reject the too frequent or violent demand response all together.In this case,two indices that measure the customer satisfaction are then introduced as constraints to reduce the impact to end-users and avoid extreme demand adjustment.To make the model solvable,a proximate decoupling technique is used to dispose the concave constraint introduced by the customer satisfaction constraints.Results from the case studies show that the proposed model can significantly reduce the operation cost of power system while the demand response meets customer satisfaction.Especially,the total start-up costs of conventional thermal units decreases dramatically due to less startup times.Moreover,compared to the consumption way satisfaction constraint,the payment satisfaction constraint has a heavier influence on the cost.

Large-scale roll-to-roll printed,flexible and stable organic bulk heterojunction photodetector

A flexible and stable photodetector shows great potential applications in intelligent wearable devices,health monitoring,and biological sensing.The high-output fabrication of flexible and stable photodetector via the large-scale printing process would accelerate its commercialization.Herein,a high performance,flexible organic bulk heterojunction(BHJ)photodetector with good stability is designed and fabricated via a large-scale roll-to-roll(R2R)micro-gravure printing technique on polyethylene terephthalate(PET)or paper substrate,in which the organic BHJ active layer is structured with[6,6]-phenyl C_(61)butyric acid methyl ester(PCBM)and a donor-acceptor copolymer,i.e.,employing 4,8-bis(2-ethylhexylthiophene)benzo[1,2-b;3,4-b′]dithiophene(BDTT)as the donor unit and 5,8-bis(5-thiophen-2-yl)-6,7-difluoro-2,3-bis(4-ethylhexyloxy-1-mata-luorophenyl)quinoxaline(ffQx)as the acceptor unit(PBDTT-ffQx).The PBDTT-ffQx/PCBM BHJ photodetector shows a broad photoresponse in ultraviolet and visible light,a high detectivity(D^(*))value up to 6.19×10^(11)Jones,and an excellent Iphoto/Idark as high as 5.6×10^(2).It exhibits excellent flexibility and stability.Its performance parameters could maintain over 80%of original values after bending 10,000 cycles or exposing in ambient condition(humidity~50%,temperature~30℃)for 50 days without any encapsulation.More importantly,the R2R micro-gravure printed PBDTT-ffQx/PCBM BHJ active layer is great homogeneous,and the responsivity(R)values of photodetector arrays show a very narrow distribution.The research results show that a high-performance PBDTT-ffQx/PCBM BHJ photodetector with well reliability and reproducibility can be fabricated via the R2R micro-gravure printing technique,which provides an available strategy for fabricating large-area and flexible electronic and optoelectronic devices.