Origin of Luminescent Centers and Edge States in Low-Dimensional Lead Halide Perovskites:Controversies,Challenges and Instructive Approaches

With only a few deep-level defect states having a high formation energy and dominance of shallow carrier non-trapping defects,the defect-tolerant electronic and optical properties of lead halide perovskites have made them appealing materials for high-efficiency,low-cost,solar cells and light-emitting devices.As such,recent observations of apparently deep-level and highly luminescent states in low-dimensional perovskites have attracted enormous attention as well as intensive debates.The observed green emission in 2D CsPb2Br5 and 0 D Cs4PbBr6 poses an enigma over whether it is originated from intrinsic point defects or simply from highly luminescent CsPbBr3 nanocrystals embedded in the otherwise transparent wide band gap semiconductors.The nature of deep-level edge emission in 2D Ruddlesden–Popper perovskites is also not well understood.In this mini review,the experimental evidences that support the opposing interpretations are analyzed,and challenges and root causes forthe controversy are discussed.Shortcomings in the current density functional theory approaches to modeling of properties and intrinsic point defects in lead halide perovskites are also noted.Selected experimental approaches are suggested to better correlate property with structure of a material and help resolve the controversies.Understanding and identification of the origin of luminescent centers will help design and engineer perovskites for wide device applications.

Effectively Inhibit Phase Separation to Improve Efficiency and Stability of All-Inorganic Planar CsPbIBr2 Perovskite Solar Cells

The advancement in a power conversion efficiency(PCE)to reach 25%,the inorganic perovskites are being explored intensively as promising optoelectronic materials due to their excellent photovoltaic performance,i.e.,thermal stability and efficiency.Lately,the inorganic cesium lead halide perovskite is studied to show enhanced light absorption,however,it suffers from the phase separate into I-rich and Br-rich phase which leads to poor film quality due to difference of electronegativity.Herein,we propose a unique solution of controlling the rate of solvent volatilization followed by gel method to inhibit phase separation effectively to obtain the homogenous and pinhole-free CsPbIBr2 films with high crystalline quality.In this study,an inverted planar device based on a light absorber of CsPbIBr2 is prepared to achieve a power conversion efficiency of 8.8%(maintain a stabilized value of 8%in ambient air conditions).Surprisingly,the optimized cell without encapsulation shows excellent long-term stability,as it maintained 90%initial efficiency over 500 h and controlled storage at around 45%relative humidity and 25℃.

甲脒/铯基卤化物钙钛矿光伏材料稳定性研究进展

低成本、高效率和长寿命是光伏材料商业化应用必须满足的黄金三角规则。目前,钙钛矿光伏材料在低成本和高效率方面已取得显著进展,但其稳定性仍面临挑战。论文总结了近年来甲脒/铯基卤化物钙钛矿太阳能电池材料稳定性策略的研究进展,包括组分、表面、应力和降维工程四种稳定策略;并进一步总结了甲脒/铯基卤化物钙钛矿太阳能电池材料动力学稳定性的研究工作,该研究将为卤化物钙钛矿太阳能电池材料的稳定策略提供参考。

Antimony doped CsPbI_(2)Br for high-stability all-inorganic perovskite solar cells

All-inorganic perovskites,adopting cesium(Cs+)cation to completely replace the organic component of A-sites of hybrid organic–inorganic halide perovskites,have attracted much attention owing to the excellent thermal stability.However,all-inorganic iodine-based perovskites generally exhibit poor phase stability in ambient conditions.Herein,we propose an efficient strategy to introduce antimony(Sb^(3+))into the crystalline lattices of CsPbI_(2)Br perovskite,which can effectively regulate the growth of perovskite crystals to obtain a more stable perovskite phase.Due to the much smaller ionic radius and lower electronegativity of trivalent Sb^(3+)than those of Pb^(2+),the Sb^(3+)doping can decrease surface defects and suppress charge recombination,resulting in longer carrier lifetime and negligible hysteresis.As a result,the all-inorganic perovskite solar cells(PSCs)based on 0.25%Sb^(3+)doped CsPbI_(2)Br light absorber and screen-printable nanocarbon counter electrode achieved a power conversion efficiency of 11.06%,which is 16%higher than that of the control devices without Sb^(3+)doping.Moreover,the Sb^(3+)doped all-inorganic PSCs also exhibited greatly improved endurance against heat and moisture.Due to the use of low-cost and easy-to-process nanocarbon counter electrodes,the manufacturing process of the all-inorganic PSCs is very convenient and highly repeatable,and the manufacturing cost can be greatly reduced.This work offers a promising approach to constructing high-stability all-inorganic PSCs by introducing appropriate lattice doping.

全无机铯铅卤钙钛矿纳米晶的表面包覆策略及白光LED应用研究进展

全无机铯铅卤钙钛矿纳米晶CsPbX_(3)(X=Cl、Br、I)具有量子产率高、载流子寿命长、带隙窄、光谱可调范围广等优异的光电性能,在发光二极管(LED)、太阳能电池、光电探测等领域有着广阔的应用前景。然而,由于离子化合物的本征特性,其在水分、光照以及温度的作用下不能稳定存在,严重阻碍了该纳米晶在光电领域的应用。近年来,科研工作者相继报道了各种提高钙钛矿纳米晶稳定性的方法,如离子掺杂、表面钝化和表面包覆等策略。与离子掺杂和表面钝化相比,表面包覆策略不仅隔离了环境因素对CsPbX_(3)纳米晶的影响,还阻止了不同阴离子组分的钙钛矿纳米晶间的阴离子交换,提高了纳米晶的稳定性。因此,本文详细介绍了全无机铯铅卤钙钛矿纳米晶的包覆机理,同时重点从聚合物薄膜、氧化物、金属有机框架和沸石等包覆材料层面介绍表面包覆策略的优越性,最后总结了复合材料在照明和显示领域的应用。

CsPbX_(3)(X=Br,I)@ZIF-8复合材料用于高效WLED器件

纯无机铯铅卤钙钛矿材料由于其高光致发光量子产率(PLQY)、高色纯度、可调带隙、高载流子迁移率在光电子器件中引起了广泛的关注。然而,水、氧条件下稳定性较差使其实际用途受到限制,为了提升水氧环境下的稳定性,在典型热注射法合成步骤中加入干燥的纳米粒子自组装方法合成的ZIF-8粉末使钙钛矿纳米晶体在ZIF-8孔隙中原位生长得到CsPbX_(3)@ZIF-8(X=Br,I)复合材料,该合成方法步骤简单,成本低廉,合成样品具有优异的稳定性,在空气中可以稳定2年以上,水中15 d后依然观察到明亮的荧光发射。以PMMA为基体材料制备的CsPbX_(3)@ZIF-8/PMMA(X=Br,I)复合膜具有良好的光学特性,分别制成绿光CsPbBr3@ZIF-8/PMMA膜发射峰波长为525 nm与红光CsPbI3@ZIF-8/PMMA膜发射峰波长为697 nm。以蓝光LED为光源制备成的WLED器件达到白光色度坐标为(0.3112,0.3334),色温6552 K,显色指数(CRI)为73.6。

Cesium lead halide perovskite triangular nanorods as high-gain medium and effective cavities for multiphoton- pumped lasing

High-performance multiphoton-pumped lasers based on cesium lead halide perovskite nanostructures are promising for nonlinear optics and practical frequency upconversion devices in integrated photonics. However, the performance of such lasers is highly dependent on the quality of the material and cavity, which makes their fabrication challenging. Herein, we demonstrate that cesium lead halide perovskite triangular nanorods fabricated via vapor methods can serve as gain media and effective cavities for multiphoton-pumped lasers. We observed blue-shifts of the lasing modes in the excitation fluence-dependent lasing spectra at increased excitation powers, which fits well with the dynamics of Burstein-Moss shifts caused by the band filling effect. Moreover, efficient multiphoton lasing in CsPbBr3 nanorods can be realized in a wide excitation wavelength range （700-1,400 nm）. The dynamics of multiphoton lasing were investigated by time-resolved photoluminescence spectroscopy, which indicated that an electron-hole plasma is responsible for the multiphoton-pumped lasing. This work could lead to new opportunities and applications for cesium lead halide perovskite nanostructures in frequency upconversion lasing devices and optical interconnect systems.

Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking

Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)3, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)3 nanocrystals are well dispersed in the ethyl cellulose(EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl2 Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)3 film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)3 based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters.

Long-lasting photoluminescence quantum yield of cesium lead halide perovskite-type quantum dots

Cesium lead halide perovskite(CsPbX_(3),X=Cl,Br,I)quantum dots(QDs)and their partly Mn^(2+)-substituted QDs(CsPb1–xMnxX3)attract considerable attention owing to their unique photoluminescence(PL)efficiencies.The two types of QDs,having different PL decay dynamics,needed to be further investigated in a form of aggregates to understand their solid-state-induced exciton dynamics in conjunction with their behaviors upon degradation to achieve practical applications of those promising QDs.However,thus far,these QDs have not been sufficiently investigated to obtain deep insights related to the long-term stability of their PL properties as aggregated solid-states.Therefore,in this study,we comparatively examined CsPbX_(3)-and CsPb1–xMnxX_(3)-type QDs stocked for>50 d under dark ambient conditions by using excitation wavelength-dependent PL quantum yield and time-resolved PL spectroscopy.These investigations were performed with powder samples in addition to solutions to determine the influence of the inter-QD interaction of the aged QD aggregates on their radiative decays.It turns out that the Mn^(2+)-substituted QDs exhibited long-lasting PL quantum efficiencies,while the unsubstituted CsPbX_(3)-type QDs exhibited a drastic reduction of their PL efficiencies.And the obtained PL traces were clearly sensitive to the sample status.This is discussed with the possible interaction depending on the size and distance of the QD aggregates.

Raman spectra and vibrational analysis of CsPbI3:A fast and reliable technique to identify lead halide perovskite polymorphs

A major issue in the development of Lead halide perovskites is the assessment of the crystal structure of the samples,due to their typically limited time-stability,and the understanding of the role of external factors that can induce a crystal phase transformation(such as humidity,intense light flux,temperature,etc.).In this perspective,it is of utmost importance to have at disposal a fast and reliable experimental tool able to give an immediate indication of the polymorph of the sample with the possibility to integrate in-situ measurements for constant monitoring.In this paper we propose Raman spectroscopy as the ideal technique to solve this problem.The vibrational analysis of CsPbI3 in the a-phase and 5-phase and of the Cs4PbI6 secondary phase is reported and all the vibrational modes are assigned by comparing experimental spectra of the phases to Raman modes calculated within the DFT framework.Finally,the mechanism of laser induced phase degradation was studied using in-situ Raman measurements providing new insights on the secondary phase generated during the process.

新型钙钛矿太阳能电池的研究进展

太阳能光伏发电是解决目前日益严重的能源与环境问题的一种有效手段,在最近几年里,新型钙钛矿太阳能电池得到迅猛发展,其最高光电转换效率已经达到20%,已成为可再生能源领域的研究热点之一。钙钛矿太阳能电池是以具有钙钛矿结构的有机-金属卤化物等作为核心光吸收、光电转换、光生载流子输运材料的太阳能电池,具有能量转换高和成本低的优点且其核心光电转换材料具有廉价、容易制备的特点,因此获得了学术界的特别关注。首先总结了钙钛矿太阳能电池的结构与原理,然后综述了钙钛矿太阳电池在结构和材料方面的最新研究进展,特别是无铅钙钛矿太阳能电池的一些研究,最后分析了钙钛矿太阳能电池的发展趋势及发展中亟需解决的问题。

静电纺丝制备高疏水性的CsPbBr_(3)纳米晶聚甲基丙烯酸甲酯复合纤维薄膜

目前,全无机钙钛矿卤化铅铯CsPbX_(3)(X=Cl,Br,I)纳米晶因具有量子产率高、荧光波长可调、半峰宽窄等优异的光学性能,成为探索光电子器件的优秀候选材料。虽然此材料的优点突出,在发光二极管(LEDs)、光电探测器、太阳能电池和下一代显示设备等方面应用广泛,但由于其稳定性差,实际应用受到限制。本工作采用静电纺丝技术,对同时溶解了纳米晶前驱体和聚甲基丙烯酸甲酯(PMMA)的N,N-二甲基甲酰胺(DMF)溶液进行静电纺丝,通过一步法在PMMA薄膜中原位生成溴化铅铯(CsPbBr_(3))纳米晶。结果表明,CsPbBr_(3)纳米晶被很好地包裹在聚合物纤维中,且分散非常均匀,在紫外灯照射下可以发出清晰且均匀的绿色荧光。纤维薄膜在水中放置超过四个月后,仍然能保持初始发光强度的70%,具有非常好的水稳定性。与传统的合成钙钛矿后混入纤维前驱体生成风干膜(ADF)的两步法相比,一步法制备钙钛矿纳米晶复合薄膜不仅为制备高稳定性钙钛矿提供了新的方法,而且使用的原材料少,工艺更简单。

铯铅卤化物钙钛矿型平面异质结LED的应用与发展

由于优异的光电性能与环境稳定性,全无机铯铅卤化物CsPbX_3(X=Cl, Br, I)钙钛矿材料自2015年起逐渐成为光电领域的研究热点,在诸多电子、光电子器件的应用研究中取得了突破性进展,受到了科学界的广泛关注。本综述结合铯铅卤化物钙钛矿型平面异质结LED的最新研究进展,对器件的结构及其工作原理进行扼要的介绍,并着重从提高LED器件发光性能和工作稳定性方面进行优化策略的归类与总结,最后就稳定高效的无机钙钛矿型平面异质结LED的发展趋势进行了展望。

全无机铯铅卤钙钛矿量子点的研究进展

全无机铯铅卤钙钛矿[Cs PbX3(X=Cl、Br、I)]量子点稳定性高、色纯度好、量子产率高,受到人们广泛关注。然而,CsPbX_(3)量子点中组分铅的毒性限制了CsPbX_(3)量子点的进一步应用,同时,如何进一步提升其性能和稳定性也备受关注。首先,对CsPbX_(3)量子点进行了简介;接着,对离子掺杂CsPbX_(3)量子点、表面包覆CsPbX_(3)量子点、表面钝化CsPbX_(3)量子点的研究进展进行了综述;离子掺杂、不同材料表面包覆、表面钝化提高了CsPbX_(3)钙钛矿量子点的稳定性。最后,对CsPbX_(3)量子点未来的发展方向进行了展望。

基于无机铅卤钙钛矿的第一性原理分析

运用Material Studio 7.0软件构建模型,对不同卤化物所构成的无机铅卤钙钛矿进行了第一性原理分析,选用了点群结构为Pm3m的CsPbX3(X=Cl,Br,I)立方晶胞,并在此基础上优化分析了带隙结构和态密度.通过调整不同的交换泛函得到了同一CsPbBr3单胞优化后的不同的带隙和体模量.并对同一泛函PBE下CsPbCl3、CsPbBr3、CsPbI3的带隙大小、态密度等结果进行了分析,结果显示,随着晶格参数从Cl到I变大,钙钛矿的体模量和电子带隙会变小,离子性也得到了增强.

钙钛矿衍生光伏材料的研究进展

钙钛矿材料凭其优异的性能登上了光伏的舞台,但其含铅毒性与不稳定性必然成为其未来发展瓶颈。因此,探索新型高效、稳定的无铅类光伏材料刻不容缓。在ABX3结构的基础上,本文对无铅、高稳定性的全无机A3B2X9结构钙钛矿、卤化物双钙钛矿中的A2B(I)B(III)X6与A2B(Ⅳ)X6、硫化物-卤化物等体系光伏材料在太阳能电池、光电探测器与发光二极管等领域的应用与探索进行综述。并在此基础上阐述了机器学习与高通量密度泛函理论计算相结合在探索新型光伏材料上的一些突破进展。最后对未来光伏材料的突破点进行展望,该工作对科研人员将来开发新兴光伏材料具有重大意义。

全无机钙钛矿量子点CsPbX_3(X=Cl,I,Br)的合成及其应用研究进展

基于钙钛矿结构的CsPbX_3(X=Cl, I,Br)量子点,以其优异的发光性能,如较高的量子效率(～90%)、发光波谱覆盖整个可见光谱(400～700 nm)和窄发射峰(12～42 nm)等,在太阳能利用和提高太阳能电池光电转化效率等前沿技术领域有着重要的应用价值.文中对近年来全无机铅卤钙钛矿CsPbX_3(X=Cl, I,Br)量子点的制备方法、性能影响因素、应用领域的研究进展进行了综述,并对其存在的不足进行了分析.以期为研发出具有优异发光性能的全无机铅卤钙钛矿量子点提供借鉴.

基于大晶粒MA0.7FA0.3PbI3的薄膜光探测器

为了研究大晶粒高质量钙钛矿薄膜对光探测器的影响,制备了晶粒尺寸超过2μm的MA0.7FA0.3PbI3薄膜,并基于该薄膜制备了光电导型的光探测器(MCP-PD)。基于该薄膜的光探测器在532 nm和3 V偏置电压下获得了高响应度(0.905 A/W)和探测度(3.18×1012 Jones)。在相似性能条件下,基于大晶粒尺寸薄膜制备的MCP-PD还表现出较快的响应速度。实验结果表明,大晶粒尺寸的薄膜降低了晶界对载流子传输的阻碍,提升了光探测器的响应度、探测度及响应速度。

CH_(3)I sensing using yttrium single atom-doped perovskite nanocrystals

Nanocrystals(NCs)of cesium lead halide perovskites are optically unstable,which prevents their use in optical sensors.The combination of perovskite NCs and metal single atoms(SAs)may be a good solution to this issue.Unfortunately,depositing metal SAs on perovskite NCs remains a challenge due to relative weak metal-halide bonds.Herein,we present that,via a photo assisted method using cesium lead halide perovskite NCs as host material to anchor Y single atoms,we successfully synthesize Y SA anchored CsPbBr_(3)NCs(Y-SA/CsPbBr_(3)NCs)with outstanding fluorescence stability through the formation of two Y-O bonds and two Y-Br bonds.In comparison to bare CsPbBr_(3)NCs,Y-SA/CsPbBr_(3)NCs possess more stable optical characteristics.The as-synthesized Y-SA/CsPbBr_(3)NCs can be employed as a colorimetric platform to perform rapid CH_(3)I sensing.Detection limit of 0.044 ppm is exhibited in this approach with excellent anti-interference performance.The YSA/CsPbBr_(3)NCs-based system has been applied to the detection of CH_(3)I in sweet potato samples with satisfying results.

Oriented inorganic perovskite absorbers processed by colloidal-phase fumigation

Inorganic perovskite absorbers are promising candidates for next-generation photovoltaics due to their good thermal and light stabilities.Halide-mixed Cs Pb I_(x)Br_(3-x)reach a compromise between its structural tolerance and absorption edge,yet the power conversion efficiencies(PCEs)of the asfabricated cells can be considerably limited by the nonideal quality of solution-processed films.Here we demonstrated a fumigation strategy on colloidal perovskite films using dualO-donor ethyl acetate(EA).By in-situ monitoring this stage with grazing-incidence wide-angle X-ray scattering technology,we reveal that EA fumigation would impose ripening barrier on colloidal inorganic perovskites and hence slow down the nucleation rate,leading to an intermediate state for processing high-crystallinity and oriented perovskite films with improved photophysical properties.An optimized PCE of 16.6%was finally yielded upon wide-bandgap(1.9 eV)perovskite absorber.