Metal-organic frameworks with mixed-ligands strategy as heterogeneous nucleation center to assist crystallization for efficient and stable perovskite solar cells

Deep-level defects and random oriented configuration in perovskite crystallization process would cause the nonradiative recombination and further affect the performance of perovskite solar cells(PSCs).Herein,two metal-organic frameworks(MOFs)with tunable Lewis-base passivation sites have been constructed(Cd-Httb and Cd-Httb-BDC,Httb=5-(4-(1H-1,2,4-triazole-1-yl)benzyl)-1h-tetrazole,BDC=1,4-dicarboxybenzene)to eliminate deep-level defects and simultaneously as nanostructured heterogeneous nucleation seed to assist the growth of large-grained perovskite films.Compared with the control and Cd-Httb,Cd-Httb-BDC designed with mix-ligands strategy exhibited the enhanced inducted effect on the crystallization and nucleation of high-quality perovskite films during annealing process.Consequently,the resultant Cd-Httb-BDC-modified device achieved higher power conversion efficiency(PCE)(22.18%)than the control(20.89%)and Cd-Httb(21.56%).Meanwhile,the unencapsulated Cd-Httb-BDC-modified device still maintained 90%of initial PCE after 1500 h in ambient conditions and exhibited enhanced thermal stability(85℃ in N_(2) atmosphere).This work presented a successful example of mixligands strategy on construction of high-quality MOF-assisted perovskite films for high-efficient and stable PSCs.

Alternative lead-free mixed-valence double perovskites for high-efficiency photovoltaic applications

Lead-based organic-inorganic hybrid perovskites have exhibited great potential in photovoltaics,achieving power conversion efficiencies(PCEs) exceeding 25%.However,the toxicity of lead and the instability of these materials under moist conditions pose significant barriers to large-scale production.To overcome these limitations,researchers have proposed mixed-valence double perovskites,where Cs_(2)Au~ⅠAu~ⅢI_6 is a particularly effective absorber due to its suitable band gap and high absorptance efficiency.To further extend the scope of these lead-free materials,we varied the trivalent gold ion and halogen anion in Cs_(2)Au~ⅠAu~ⅢI_6,resulting in 18 new structures with unique properties.Further,using first-principles calculations and elimination criteria,we identified four materials with ideal band gaps,small effective carrier mass,and strong anisotropic optical properties.According to theoretical modeling,Cs_(2)AuSbCl_6,Cs_(2)AuInCl_6,and Cs_(2)AuBiCl_6 are potential candidates for solar cell absorbers,with a spectroscopic limited maximum efficiency(SLME) of approximately 30% in a 0.25 μm-thick film.These three compounds have not been previously reported,and therefore,our work provides new insights into potential materials for solar energy conversion.We aim for this theoretical exploration of novel perovskites to guide future experiments and accelerate the development of high-performance photovoltaic devices.

Crystallization Regulation and Morphological Evolution for HTM-free Tin-Lead (1.28eV) Alloyed Perovskite Solar Cells

There have been huge achievements of all-perovskite tandem solar cells,which recently realized the highest power conversion efficiency of 24.8%.However,the complex device structure and complicated manufacture processes severely restrict the further development of all-perovskite tandem solar cells.In this work,we successfully fabricated high-efficiency hole transport material-free(HTM-free)Sn−Pb alloyed narrow bandgap perovskite solar cells(PSCs)by introducing guanidinium thiocyanate(GASCN)and hydroiodic acid(HI)into the perovskite precursor solution.GASCN and HI play a positive synergy effect during perovskite crystallization process resulting in larger grain size,fewer surface defects,and lower trap density to suppress the Sn^(2+)oxidation degradation.Furthermore,they could effectively adjust the energy level of perovskite materials,reduce the energy level difference between perovskite and ITO resulting in more efficiently transport of free hole charge carriers.As a result,with adding GASCN and HI,the achieved highest power conversion efficiency of HTM-free devices increased from 12.58%to 17.85%,which is one of the highest PCEs among all values reported to date for the HTM-free narrow-bandgap(1.2-1.4 eV)Sn−Pb binary PSCs.Moreover,the optimized device shows improved environmental stability.Our additive strategy manifests a remarkable step towards the facile,cost-efficient fabrication of HTM-free perovskite-based tandem solar cells with both high efficiency and simple fabrication process.

Stability of mixed-halide wide bandgap perovskite solar cells: Strategies and progress

Benefiting from the superior optoelectronic properties and low-cost manufacturing techniques,mixedhalide wide bandgap(WBG)perovskite solar cells(PSCs)are currently considered as ideal top cells for fabricating multi-junction or tandem solar cells,which are designed to beyond the Shockley-Queisser(S-Q)limit of single-junction solar cells.However,the poor long-term operational stability of WBG PSCs limits their further employment and hinders the marketization of multi-junction or tandem solar cells.In this review,recent progresses on improving environmental stability of mixed-halide WBG PSCs through different strategies,including compositional engineering,additive engineering,interface engineering,and other strategies,are summarized.Then,the outlook and potential direction are discussed and explored to promote the further development of WBG PSCs and their applications in multijunction or tandem solar cells.

Recent advances in Pb-Sn mixed perovskite solar cells

Organic-inorganic hybrid lead-tin perovskite solar cells(Pb-Sn PSCs)have attracted much attention because of their advantages of low toxicity,variable bandgap,and feasibility for all-perovskite tandem solar cells,and the current power conversion efficiency(PCE)has exceeded 23%.However,due to the rambunctious crystallization process,easily oxidized Sn(Ⅱ)and inadequate energy level arrangement,there are many defects in perovskite films resulting in serious carrier recombination,which makes PCE still lag Pb-based PSCs.The quality of perovskite films is an important factor affecting the overall device performance.The selection and optimization of transport layers not only determines the interface energy level arrangement but also affects the carrier transport.In this paper,the research progress in improving performance of Pb-Sn PSCs in recent years is reviewed from aspects of perovskite layer and transport layers.The profound understanding of different promotion methods is summarized as well.These results have certain guiding significance for the future development and commercial application of Pb-Sn PSCs.

Progress of Pb-Sn Mixed Perovskites for Photovoltaics: A Review

Pb-Sn mixed perovskites are becoming increasingly popular as narrowbandgap(1.2–1.3 eV)light absorbers in single-junction perovskite solar cells(PSCs)and as bottom cells for all-perovskite tandem solar cells,for highefficiency,low-cost,lightweight,roll-to-roll printable photovoltaic(PV)applications.From the first report of planar Pb:Sn mixed PSCs in 2014,the power conversion efficiencies(PCE)have increased from 10%to 21%by the end of 2020 with an exponential growth in research conducted in this field.Despite much effort,the performance and stability of Pb-Sn mixed PSCs are still limited,which constrains their long-term use in all-perovskite tandem devices.This review highlights the avenues explored in improving different aspects of Pb-Sn mixed PSCs and provides a comprehensive discussion of the interdependent factors affecting the device performance.This includes compositional engineering of the perovskite crystal,absorber layer fabrication and crystallization methods,bandgap tuning,Sn4+reduction,and surface passivation of the absorber layer,as well as the selection of interlayers and electrodes of the final PSC.

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.

Stability of Sn-Pb mixed organic–inorganic halide perovskite solar cells:Progress,challenges,and perspectives

The exploration of low bandgap perovskite material to approach Shockley-Queisser limit of photovoltaic device is of great significance,but it is still challenging.During the past few years,tin–lead(Sn-Pb)mixed perovskites with low bandgaps have been rapidly developed,and their single junction solar cells have reached power conversion efficiency(PCE)over 21%,which also makes them ideal candidate as low bandgap sub-cell for tandem device.Nevertheless,due to the incorporation of unstable Sn^(2+),the stability issue becomes the vital problem for the further development of Sn-Pb mixed perovskite solar cells(PSCs).In this review,we are dedicated to give a full view in current understanding on the stability issue of SnPb mixed perovskites and their PSCs.We begin with the demonstration on the origin of instability of Sn-Pb mixed perovskites,including oxidation of Sn^(2+),defects,and interfacial layer induced instability.Sequentially,the up-to-date developments on the stability improvement of Sn-Pb mixed perovskites and their PSCs is systematically reviewed,including composition engineering,additive engineering,and interfacial engineering.At last,the current challenges and future perspectives on the stability study of Sn-Pb mixed PSCs are discussed,which we hope could promote the further application of Sn-Pb mixed perovskites towards commercialization.

A-site phase segregation in mixed cation perovskite

Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability.However,adverse impact also accompanies the mixed cation system simultaneously.It brings the compositional instability,wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process,thus resulting in the efficiency reduction of perovskite solar cells(PSCs)devices.This review focuses on the cation induced phase segregation,and elucidates the segregation mechanisms from the perspectives of film formation and ageing process,respectively.Furthermore,the influence of cation segregation on device performance and operational stability are discussed.And based on these understandings,viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.

Understanding the precursor chemistry for one-step deposition of mixed cation perovskite solar cells by methylamine route

Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization.The slow evaporation of frequently used solvents(DMF or DMSO) limits the fast perovskite layer crystallization,hindering their implementation in large scale deposition methods.Alternatively,methylamine-based precursors have demonstrated rapid crystallization,leading to uniform and specular films.Nonetheless,their application has been limited to MAPbI3 perovskites with limited efficiency and stability.In this work,we report the requirements for stabilizing α-phase of mixed cation perovskites with high amount of formamidinium by using a methylamine-based precursor.We found that even though,there are many methods for incorporating the methylamine(MA) in precursors or films;the MA content determines stabilization of the α-phase and therefore the viscous-solution route is the only method to incorporate high amounts of MA.At low amounts of MA,perovskite tend to crystallize in 1D dimensional FA_(3)(MA)PbI5 phases due to the incomplete solvation of the PbI6-clusters.In contrast,high MA ratio induces a full solvation of the clusters,leading to a rapid crystallization and a full stabilization of the active 3D α-phase.These results open a window in the development and understanding of new precursors for the fabrication of high efficient,stable and scalable perovskite devices.

A mixed-cation lead iodide MA_(1-x)EA_xPbI_3 absorber for perovskite solar cells

The mixed-cation lead halide perovskites have emerged as a new class of promising light harvesting materials for solar cells. The formamidinium（FA）, methylammonium（MA） and Cs cations are widely studied in the field of mixed-cation perovskites. Here, we have investigated ethylammonium（EA） as an alternative cation to fabricate a mixed-cation perovskite of MA_（1-x）EA_xPbI_3. We have characterized the materials using the X-ray diffraction（XRD）, scanning electron microscope（SEM）, and UV–vis spectrum. Our results have confirmed the successful incorporation of EA cations into MAPbI_3. Interestingly, the optimal amount of EA to achieve the best performance is quite low. This is different from the FA–MA mixed-cation perovskites although EA and FA have similar radii. In short, the EA–MA mixed-cation perovskite has some material and device properties highly distinguishable from the FA–MA one.

Lattice reconstruction for mixed-halide blue perovskite light-emitting diodes with high brightness,outstanding color stability and low efficiency roll-off

We report a simple,effective,and universal lattice reconstruction approach to improve the quality of perovskite films by using nonpolar solvents with high Gutmann donor numbers(DNs).We find that high-DN nonpolar solvents,for instance,ethyl acetate,can interact with perovskite precursors.Such a solvent can make the perovskite lattice more ordered and“harder”and promote the formation of heterostructures with low-dimensional perovskite impurities and residual solvent molecules.As a result,the latticereconstructed perovskite films exhibit reduced defect densities and suppressed ion migration.The resultant mixed-halide blue perovskite light-emitting diodes(PeLEDs)show greatly enhanced tolerance to high driving current densities and voltages,demonstrating high brightness,outstanding color stability and low efficiency roll-off.Our work provides a deep understanding of the interactions between nonpolar solvents and perovskites and offers useful guidelines for further development of high-power PeLEDs.

A Novel Zirconium-Based Perovskite-Type Membrane Material for Oxygen Permeation

A novel zirconium-based membrane material of BaCo0.4Fe0.4Zr0.2O3-6 with cubic perovskite structure was synthesized for the first time through a method of citric and EDTA acid combined complexes. The structural stability was characterized by XRD, O-2-TPD and H-2-TPR techniques respectively. The high oxygen permeation flux of 0.873 mL/cm(2) min at 950 degreesC was obtained under He/Air gradient. Meanwhile, the single activation energy for oxygen permeation and the long-term steady operation of 200 h at 800 degreesC were achieved.

Structure and Conductivity of Perovskite-Type LnFe_xCo_(1-x)O_3

The perovskite-type solid oxides (ABO3) were a novel kind of functional material with superior properties and have found wide application. A series of nanocrystalline mixed oxides LnFexCo1-xO3 (Ln=La, Pr, Sm, Dy, Er)were prepared by sol-gel method. Several aspects of the perovskite type LnFexCo1-xO3, such as crystal defects, oxygen ion vacancy, the tolerance factor of the ABO3, col size, and the bond energy of chemical bond, searching for the relationship between the conductivity and structure of the perovskite type LnFexCo1-xO3, hoping to find some regularities in theory, and providing some helps for composing new type of electricity materials.

High performance flexible Sn-Pb mixed perovskite solar cells enabled by a crosslinking additive

Flexible perovskite solar cells(PSCs)have drawn increasing attention due to their promising applications for wearable electronics and aerospace applications.However,the efficiency and stability of flexible PSCs still lag behind their rigid counterparts.Here,we use N,N-dimethyl acrylamide(DMAA)to in situ synthesize cross-linking polymer for flexible Sn–Pb mixed PSCs.DMAA can gather at grain boundary as a scaffold to regulate the crystallization of perovskite and reduce defects.The rigid and flexible Sn–Pb mixed PSCs showed efficiencies of 16.44%and 15.44%,respectively.In addition,the flexible Sn–Pb mixed PSCs demonstrated excellent bending durability,which retained over 80%of the original efficiency after 5000 bending cycles at a radius of 5 mm.

Role of chloride on the instability of blue emitting mixed‑halide perovskites

Although perovskite light-emitting diodes(PeLEDs)have seen unprecedented development in device efciency over the past decade,they sufer signifcantly from poor operational stability.This is especially true for blue PeLEDs,whose operational lifetime remains orders of magnitude behind their green and red counterparts.Here,we systematically investigate this efciency-stability discrepancy in a series of green-to blue-emitting PeLEDs based on mixed Br/Cl-perovskites.We fnd that chloride incorporation,while having only a limited impact on efciency,detrimentally afects device stability even in small amounts.Device lifetime drops exponentially with increasing Cl-content,accompanied by an increased rate of change in electrical properties during operation.We ascribe this phenomenon to an increased mobility of halogen ions in the mixed-halide lattice due to an increased chemically and structurally disordered landscape with reduced migration barriers.Our results indicate that the stability enhancement for PeLEDs might require diferent strategies from those used for improving efciency.

Anisotropic emission of orientation-controlled mixed-dimensional perovskites for light-emitting devices

Perovskite light-emitting diodes(PeLEDs)are attracting increasing attention owing to their impressive efficiencies and high luminance across the full visible light range.Further improvement of the external quantum efficiency(EQE)of planar PeLEDs is limited by the light out-coupling efficiency.Introducing perovskite emitters with directional emission in PeLEDs is an effective way to improve light extraction.Here,we report that it is possible to achieve directional emission in mixed-dimensional perovskites by controlling the orientation of the emissive center in the film.Multiple characterization methods suggest that our mixed-dimensional perovskite film shows highly orientated transition dipole moments(TDMs)with the horizontal ratio of over 88%,substantially higher than that of the isotropic emitters.The horizontally dominated TDMs lead to PeLEDs with exceptional high light out-coupling efficiency of over 32%,enabling a high EQE of 18.2%.

锗溴混合掺杂调控钙钛矿太阳电池光电特性的第一性原理研究

采用第一性原理方法对锗溴混合掺杂下甲胺基钙钛矿(MAPbI3)材料的能带结构、态密度、介电函数和吸收光谱进行研究。构建MAPbI_(3)、MAPb_(0.75)Ge_(0.25)I_(3)、MAPbI_(2.5)Br_(0.5)、MAPb_(0.75)Ge_(0.25)I_(2.5)Br_(0.5)这4种钙钛矿结构模型并优化其结构,得出光电特性。研究结果表明,锗溴混合掺杂可改变价带顶与导带底位置及斜率,调控带隙值大小,同时混合掺杂也会改变价带顶与导带底的斜率,4种钙钛矿模型中锗溴混合掺杂时价带顶与导带底的斜率最小,有利于电子跃迁,提升光电转换效率;掺杂锗可提高钙钛矿在可见光区的吸收性能,掺杂溴对钙钛矿光学特性影响不大。

Alkalis-doping of mixed tin-lead perovskites for efficient near-infrared light-emitting diodes

Substitution of lead(Pb)with tin(Sn)is a very important way to reduce the bandgap of metal halide perovskite for applications in solar cells,and near infrared(NIR)light-emitting diodes(LEDs),etc.However,mixed Pb/Sn perovskite becomes very disordered with high trap density when the Sn molar ratio is less than 20%.This limits the applications of mixed Pb/Sn perovskites in optoelectronic devices such as wavelength tunable NIR perovskite LEDs(Pe LEDs).In this work,we demonstrate that alkali cations doping can release the microstrain and passivate the traps in mixed Pb/Sn perovskites with Sn molar ratios of less than 20%,leading to higher carrier lifetime and photoluminescence quantum yield(PLQY).The external quantum efficiency(EQE)of Sn_(0.2)Pb_(0.8)-based NIR Pe LEDs is dramatically enhanced from 0.1%to a record value of 9.6%(emission wavelength:868 nm).This work provides a way of making high quality mixed Pb/Sn optoelectronic devices with small Sn molar ratios.

High-throughput compositional mapping of triple-cation tin-lead perovskites for high-efficiency solar cells

Mixed tin-ead perovskites suffer from structural instability and rapid tin oxidation;thus,the investigation of their optimal composition ranges is important to address these inherent weaknesses.The critical role of triple cations in mixed Sn–Pb iodides is studied by performing a wide range of compositional screenings over mechanochemically synthesized bulk and solution-processed thin films.A ternary phase map of FA(Sn_(0.6)Pb_(0.4))I_(3),MA(Sn_(0.6)Pb_(0.4))I_(3),and Cs(Sn_(0.6)Pb_(0.4))I_(3)is formed,and a promising composition window of(FA_(0.6-x)MA_(0.4)Cs_(x))Sn_(0.6)Pb_(0.4)I_(3)(0≤x≤0.1)is demonstrated through phase,photoluminescence,and stability evaluations.Solar cell performance and chemical stability across the targeted compositional space are investigated,and FA_(0.55)MA_(0.4)Cs_(0.05)Sn_(0.6)Pb_(0.4)I_(3)with strain-relaxed lattices,reduced defect densities,and improved oxidation stability is demonstrated.The inverted perovskite solar cells with the optimal composition demonstrate a power conversion efficiency of over 22%with an open-circuit voltage of 0.867 V,which corresponds to voltage loss of 0.363 V,promising for the development of narrow-bandgap perovskite solar cells.