Resolving Mixed Intermediate Phases in Methylammonium-Free Sn-Pb Alloyed Perovskites for High-Performance Solar Cells

The complete elimination of methylammonium(MA)cations in Sn-Pb composites can extend their light and thermal stabilities.Unfortunately,MA-free Sn-Pb alloyed perovskite thin films suffer from wrinkled surfaces and poor crystallization,due to the coexistence of mixed intermediate phases.Here,we report an additive strategy for finely regulating the impurities in the intermediate phase of Cs_(0.25)FA_(0.75)Pb_(0.6)Sn_(0.4)I_(3)and,thereby,obtaining high-performance solar cells.We introduced d-homoserine lactone hydrochloride(D-HLH)to form hydrogen bonds and strong Pb-O/Sn-O bonds with perovskite precursors,thereby weakening the incomplete complexation effect between polar aprotic solvents(e.g.,DMSO)and organic(FAI)or inorganic(CsI,PbI_(2),and SnI_(2))components,and balancing their nucleation processes.This treatment completely transformed mixed intermediate phases into pure preformed perovskite nuclei prior to thermal anneal-ing.Besides,this D-HLH substantially inhibited the oxidation of Sn^(2+) species.This strategy generated a record efficiency of 21.61%,with a Voc of 0.88 V for an MA-free Sn-Pb device,and an efficiency of 23.82%for its tandem device.The unencapsulated devices displayed impressive thermal stability at 85℃ for 300 h and much improved continuous operation stability at MPP for 120 h.

Formation and Growth Kinetics of Intermediate Phases in Ni-Al Diffusion Couples

Formation and growth of the intermediate phases in the Ni-Al diffusion couples prepared by pouring technique were investigated. Electron probe microanalysis, scanning electron microscopy and X-ray diffraction were used to characterize the product phases in the joints. The results show that two intermediate phases form in the sequence of NiAl3 and Ni2Al3 during solidification. After annealed, Ni2Al3 and NiAl3 still exist in the joints of the couples. The reasons for the formation of Ni2Al3 and NiAl3, as well as the absence of NiAl, Ni5Al3 and Ni3Al were discussed, respectively. The growth kinetics of both product phase layers indicates that their growth obeys the parabolic rate law. The activation energies and frequency factors for NiAl3 and Ni2Al3 phases were also calculated according to the Arrhenius equation.

Intermediate phase-assisted growth of CsPbBr_(3) for high performance of carbon-based perovskite solar cells

CsPbBr_(3)inorganic perovskites have been regarded as the promising materials in the field of photo-voltaics because of the high tolerance against environment.The high energy barrier of phase transition from lead bromide(PbBr_(2))to CsPbBr_(3)perovskite and low solubility of perovskite in organic solvent impede the further improvement of device performance in terms of CsPbBr_(3)solar cells.Herein,an intermediate phase-assisted growth of CsPbBr_(3)perovskite was proposed by introducing tetraphenylphosphonium bromide(TPPB)as additive.The TPPB is expected to react with PbBr_(2)in organic solvent to form an intermediate phase of[TPPB.DMF]-PbBr_(2),which not only effectively improves the crystallinity of PbBr2 crystals,but also greatly reduces the phase transition energy barrier,leading to uniform and compact CsPbBr_(3)perovskite films with large grain size and high crystallinity.In combination with carbon electrode,the CsPbBr_(3)solar cells yield a champion device performance of 9.57%in comparison of pristine CsPbBr_(3)solar cells showing a low efficiency of 8.17%.Furthermore,the intermediate phaseassisted growth of CsPbBr_(3)-based solar cells displays an outstanding storage over720 h.

Grain size control in quasi-two-dimensional perovskite thin film via intermediate phase engineering for efficient bound exciton generation

Quasi-two dimensional(2D)perovskites have emerged as a promising class of materials due to their remarkable photoluminescence efficiency,which stems from their exceptionally high exciton binding energies.The spatial confinement of excitons within smaller grain sizes could enhance the formation of biexcitons leading to higher radiative recombination efficiency.However,the synthesis of high-quality quasi-2D perovskite thin films with controllable grain sizes remains a challenging task.In this study,we present a facile method for achieving quasi-2D perovskite thin films with controllable grain sizes ranging from 500 to 900 nm.This is accomplished by intermediate phase engineering during the film fabrication process.Our results demonstrate that quasi-2D perovskite films with smaller grain sizes exhibit more efficient bound exciton generation and a reduced stimulated emission threshold down to 15.89µJ cm^(−2).Furthermore,femtosecond transient absorption measurements reveal that the decay time of bound excitons is shorter in quasi-2D perovskites with smaller grain sizes compared to that of those with larger grains at the same pump density,which is 230.5 ps.This observation suggests a more efficient exciton recombination process in the smaller grain size regime.Our findings would offer a promising approach for the development of efficient bound exciton lasers.

Intermediate phase assisted sequential deposition of reverse-graded quasi-2D alternating cation perovskites for MA-free perovskite solar cells

One-step deposition approaches have been widely applied and developed in the fabrication of quasi-2D perovskites.However,the regulation of quantum wells(QWs)and crystalline orientation is difficult and complicated when using this methodology.Sequential deposition is another widespread synthetic approach for preparing perovskite films and perovskite dimension engineering.In this article,δ-CsPbI_(3)intermediate phase assisted sequential(IPAS)deposition is successfully carried out to fabricate MA-free quasi-2D ACI perovskites.The amount of theδ-CsPbI_(3)intermediate phase in the PbI2 layer and the concentration of GAI molecule in the IPA solution both play important roles in the production of MA-free quasi-2D ACI perovskite films.The n value of the MA-free quasi-2D ACI perovskites can be adjusted,which affects the photovoltaic performance and device stability.Compared with one-step deposition,the MA-free quasi-2D ACI perovskites prepared via IPAS deposition have opposite reverse-graded QW distribution and improved vertical orientation,leading to a remarkable PEC of up to 18.86%and allowing the preparation of unpackaged devices with prominent working stability(80%,400 h).The underlying mechanism and crystallization pathway of IPAS deposition confirm that sequential deposition has unique superiority in regulating the QW distribution and crystalline orientation of quasi-2D perovskites.

pH-dependent leaching mechanism of carbonatitic chalcopyrite in ferric sulfate solution

The dissolution of a carbonatitic chalcopyrite(CuFeS2)was studied in H_(2)SO_(4)−Fe_(2)(SO_(4))_(3)−FeSO_(4)−H_(2)O at varying pH values(0.5−2.5)and 25℃ for 12 h.Experiments were conducted with a size fraction of 53−75μm.Low Cu recoveries,below 15%,were observed in all pH regimes.The results from the XRD,SEM−EDS,and optical microscopic(OM)analyses of the residues indicated that the dissolution proceeded through the formation of transient phases.Cu_(3.39)Fe_(0.61)S_(4) and Cu_(2)S were the intermediate phases at pH 0.5 and 1.0,respectively,whereas Cu_(5)FeS_(4) was the major mineral at pH 1.5 and 1.8.The thermodynamic modelling predicted the sequential formation of CuFeS_(2)→Cu_(5)FeS_(4)→Cu_(2)S→CuS.The soluble intermediates were Cu_(5)FeS_(4) and Cu2S,whilst,CuS and Cu_(3.39)Fe_(0.61)S_(4) were the refractory phases,supporting their cumulating behaviour throughout the dissolution.The obtained results suggest that the formation of CuS and Cu_(3.39)Fe_(0.61)S_(4) could contribute to the passive film formed during CuFeS_(2) leaching.

Influence of Alternative Magnetic Field on the Diffusion of Al and Mg

The influence of an alternative magnetic field on the diffusion of Al and Mg in AI-Mg diffusion couple is studied. The diffusion zone is composed of two intermediate phases, namelyβ and γ phase. Thickness of each intermediate phase is examined. The results show that the alternative magnetic field increases the thicknesses of βand γ phase zone and the layer growth ofβ and γphase obeys the parabolic rate law. The growth rate of the β and γ phase are increased with the application of the alternative magnetic field. This change is manifested through a change in the frequency factor k0 and not through a change in the activation energy Q. The frequency factor k0 for intermediate phase growth with an alternative magnetic field is 39.95 cm2/s for 7 phase and 2.84×10-4 cm2/s for β phase compared with those without the magnetic field is 22.4 cm2/s for 7 phase and 1.53×10-4 cm2/s for β phase.

Study on reaction mechanism of YBa_2Cu_3O_(7-x) film by TFA-MOD process

This paper systematically investigates the intermediate phases of YBa2Cu3O7-x （YBCO） film prepared by metalorganic deposition method using trifluoroacetates （TFA-MOD）. According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y203 and CuO after the pyrolysis process. Then these inter- mediate phases converted into tetragonal YBa2Cu3O6.5 at about 725 ℃. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures （40-140 hPa） showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.

Grain growth behavior and properties of high-entropy pseudobrookite(Mg,Co,Ni,Zn)Ti_(2)O_(5) ceramics

It is well known that the grain size of high-entropy ceramics is quite small owing to the sluggish diffusion effect. However, abnormal grain growth often occurs in high-entropy pseudobrookite ceramics, ultimately resulting in the formation of many abnormally grown grains with a grain size as large as 50 μm. To study this phenomenon, the grain growth behavior of high-entropy pseudobrookite ceramics was systematically investigated in this paper. The results demonstrate that the starting material powders first react with each other to form a high-entropy intermediate phase and calcined TiO_(2) powders (TiO_(2)-1100 ℃), and then as the sintering temperature increases, the formed high-entropy intermediate phase further reacts with TiO_(2)-1100 ℃ to form high-entropy pseudobrookite ceramics. Thus, in this system, in addition to the sluggish diffusion effect, the grain sizes of the high-entropy intermediate phase and TiO_(2)-1100 ℃ also affect the morphology of high-entropy pseudobrookite. Compared to nanosized TiO_(2), micron-sized TiO_(2) has a lower sintering activity. Therefore, the high-entropy intermediate phases (Mg,Co,Ni,Zn)TiO_(3) and TiO_(2)-1100 ℃ prepared with micron-sized starting materials exhibit lower grain sizes, finally resulting in the formation of high-entropy (Mg,Co,Ni,Zn)Ti_(2)O_(5) with small grain sizes. Moreover, nano-indentation and thermal conductivity tests were carried out on high-entropy (Mg,Co,Ni,Zn)Ti_(2)O_(5) with different morphologies. The results show that the hardness of high-entropy (Mg,Co,Ni,Zn)Ti_(2)O_(5) increases from 6.05 to 9.95 GPa as the grain size increases, whereas the thermal conductivity decreases from 2.091±0.006 to 1.583±0.006 W·m^(−1)·K^(−1). All these results indicate that high-entropy (Mg,Co,Ni,Zn)Ti_(2)O_(5) with a small grain size is a potential material for thermal protection.

Influence of Pre-deformation on Phase Transformations and Microstructures in NearβTi Alloy During Aging

The influence of pre-deformation on phase transformations,microstructures and hardening response in nearβTi alloy Ti5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe(wt%)during aging treatment was studied.The results show that obviousαphase refinement and stronger age hardening effect can be achieved when the alloy is slightly deformed before aging treatment.Because the formation of intermediate phases(O′,ωand O′′)suppresses long-range stress induced martensitic transformation and mechanical twinning,the alloy is mainly deformed via dislocation slipping during loading.Large numbers of crystal defects are generated during predeformation.With increasing the predeformation,the number density of dislocations increases gradually.These crystal defects generated by pre-deformation may partly annihilate upon early aging,but the precipitation ofαcan also be promoted,resulting in refinedαprecipitates.In the sample with 5%pre-strain,the average thickness ofαprecipitates decreases by 57%after aging at 600℃ compared with the sample without pre-strain,and the number density increases from 7.0±1 laths/μm^(2)to 22.0±3 laths/μm^(2).Some platelet-shapedαphases form when the samples experience comparably large pre-strains such as 12%and 20%.It proves that the refinedαprecipitates and better hardening effect can be achieved by pre-deformation plus aging treatment for titanium alloy.

Facile Exfoliation of Two-Dimensional Crystalline Monolayer Nanosheets from an Amorphous Metal-Organic Framework

The large-scale preparation ofmonolayer two-dimensional(2D)material remains a great challenge,which hinders its real-world applications.Herein,we report a novel layered metal–organic framework(MOF),IPM-1,whichwas synthesized froma cage-like organic linker,with extremely weak interlaminar interaction.When subjected to external disturbance,IPM-1 degenerated into an intermediate state between the crystalline and amorphous phase,in which the layers retain the inplane two-dimensional periodic structure but aremisaligned in the third dimension,leading to the loss of apparent porosity and crystallinity.This amorphous IPM-1 is readily exfoliated at gramscale into crystalline 2D nanosheets with a thickness of 1.15 nm,excellent thickness homogeneity,lateral size up to 10μm,and restored microporosity.IPM-1 nanosheets exhibit high chemical stability and catalytic activity in the oxidation of alcohol,combining the advantages of both homogeneous and heterogeneous catalyst.This work underscores that MOFs without apparent crystallinity can be ideal precursors for the successful preparation of 2D crystalline monolayer nanosheets.

Atomic-scale observation of a two-stage oxidation process in Cu2O

Atomic-scale oxidation dynamics of Cu2O nanocrystallines （NCs） are directly observed by in situ high-resolution transmission electron microscopy. A two-stage oxidation process is observed： （1）The initial oxidation stage is dominated by the dislocation-mediated oxidation behavior of Cu2O NCs via solid-solid transformations, leading to the formation of a new intermediate CuOx phase. The possible crystal structure of the CuOx phase is discussed. （2） Subsequently, CuOx is transformed into CuO by layer-by-layer oxidation. These results will help in understanding the oxidation mechanisms of copper oxides and pave the way for improving their structural diversity and exploiting their potential industrial applications.