Ni2+掺杂和卤素空位填充协同抑制CsPbBr3纳米晶体中的离子迁移

卤化铅钙钛矿(LHPs)由于具有优异的光电性能和制备成本低等优点,已成为新一代光电器件的有力候选材料。然而,缺陷造成的离子迁移会导致LHPs纳米晶的晶体结构解离分解。因此,稳定性成为LHPs实际应用中亟待解决的问题。本文旨在研究镍离子替位掺杂及卤素空位填补对CsPbBr3纳米晶中的离子迁移抑制作用。通过离子迁移活化能的测定和高分辨透射电镜的原位观察,分析了前驱体掺杂剂对加强LHPs稳定性的作用原理。首先,选用乙酰丙酮镍和溴化镍作为掺杂剂,合成了掺杂LHPs纳米晶。其次,通过吸收-荧光光谱,X射线衍射,X射线光电子衍射,透射电子显微镜等测试手段对掺杂样品的光学及化学组成进行分析。最后,通过纳米晶薄膜电导率的温度依赖关系计算出其离子迁移活化能,并结合高分辨电镜原位观察纳米晶在高能电子束辐照下的形貌演变过程,揭示了不同掺杂剂对合成掺杂LHPs稳定性的影响。实验结果表明:Ni²⁺掺杂CsPbBr3样品的离子迁移活化能相较本征CsPbBr3样品(0.07 eV)有显著提升,其中乙酰丙酮镍掺杂样品的离子迁移活化能为0.238 eV,溴化镍掺杂样品的离子迁移活化能为0.487 eV。另外,电子束辐照测试表明溴化镍掺杂钙钛矿晶体表现出更高的结构稳定性,这主要归因于掺杂的Ni²⁺对卤素的强结合和卤素填补空位缺陷的协同钝化作用。Ni²⁺掺杂和卤素空位填充协同可以有效抑制卤化物钙钛矿纳米晶体中的离子迁移。     

Ion migration in metal halide perovskite QLEDs and its inhibition

Benefiting from the excellent properties such as high photoluminescence quantum yield (PLQY), wide gamut range, and narrow emission linewidth, as well as low-temperature processability, metal halide perovskite quantum dots (QDs) have attracted wide attention from researchers. Despite tremendous progress has been made during the past several years, the commercialization of perovskite QDs-based LEDs (PeQLEDs) is still plagued by the instability. The ion migration in halide perovskites is recognized as the key factor causing the performance degradation of PeQLEDs. In this review, the elements species of ion migration, the effects of ion migration on device performance and stability, and effective strategies to hinder/mitigate ion migration in PeQLEDs are successively discussed. Finally, the forward insights on the future research are highlighted.     

Could two-dimensional perovskites fundamentally solve the instability of perovskite photovoltaics

The high efficiency and low production cost enable the halide perovskite solar cells as a promising technology for the next generation photovoltaics. Nevertheless, the relatively poor stability of the organic-inorganic halide perovskites hinders their commercial applications. In the past few years, two-dimensional (2D) perovskite has emerged as a more stable alternative to the three-dimensional (3D) counterparts and attracted intense research interests. Although many attempts and advances have been made, it is still ambiguous that whether the 2D perovskites could bring closure to the stability issue. To answer this essential question, a systematic study of the nature of 2D halide perovskites is necessary. Here, we focus on the stability investigations of 2D perovskites from different perspectives, especially light, heat, ion migration and strain. Several remaining challenges and opening problems are also discussed. With further material and device engineering, we believe that the 2D perovskites would promote perovskite solar cells to a promising future.     

Recent advances in controlling the crystallization of two-dimensional perovskites for optoelectronic device

Though three-dimensional (3D) organic–inorganic halide perovskites (OIHP) is very promising for low cost and distributed PV generation, the stability issue of 3D OIHP is still a problem for its commercialization. Two-dimensional (2D) perovskites, protected by periodic organic ligands, is promising due to its excellent optoelectronic property and superior stability. However, 2D perovskite is anisotropic in its crystal structure and optoelectronic properties, and the resulted film is often a mixture of different phase. So, methods to manipulate 2D perovskite crystal orientation and its phase separation are vital. In this review, the major advances on the composition engineering, crystal orientation, phase separation, and interfacial capping are summarized. Besides, efforts on understanding the formation process of 2D perovskite crystal are also discussed, which is important for making full use of 2D perovskite in functional optoelectronic devices.     

Investigation of highly luminescent inorganic perovskite nanocrystals synthesized using optimized ultrasonication method

All-inorganic halide perovskite nanocrystals are next-generation materials with excellent optical and semiconductor properties suitable for display applications. In this study, we introduce an optimized ultrasonication method for the high-capacity synthesis of highly luminescent inorganic perovskite nanocrystals. After the synthesis of CsPbBr₃ with superior optical performance by ultrasonication method, halide anion exchange was performed to tune the stable emission wavelength over the entire visible range. In particular, the maximum photoluminescence wavelengths of the red and green perovskite nanocrystals were appropriate for light-emitting diode applications, and their full-width-at-half-maximum were very narrow, showing outstanding color purity. The materials also had excellent thermal and photo-stability, which is a necessary requirement for perovskite nanocrystal/organic light-emitting diode hybrid device applications. We formulated uniformly stable perovskite nanocrystal inks and optimized their physical and rheological properties for successful inkjet-printing. Finally, we fabricated a hybrid device with a color conversion layer based on the red and green perovskite nanocrystals synthesized using the optimized ultrasonication and halide-ion-exchange methods. The color reproduction range of the fabricated devices was 27.3 % wider than that of the National Television System Committee values, indicating very vivid colors.     

钙钛矿晶体的电荷复合动力学研究

本文利用紫外吸收光谱和稳态荧光光谱技术结合理论模型,研究了钙钛矿材料CH₃NH₃PbI₃晶体在光激发过程中的电荷复合动力学行为,进而获得晶体的扩散长度. 电荷载体的扩散长度是判断光电材料的重要参数. 研究通过合成两种不同缺陷态浓度的CH₃NH₃PbI₃晶体,测量这两种晶体在0.019∽4.268 μJ/cm²的激光激发下的时间分辨荧光光谱,利用动力学模型对光谱进行拟合,可以获得每个晶体的掺杂浓度,空穴浓度以及电荷复合参数. 将这些参数结合已有公式,最终可获得每个晶体的电荷载体的扩散长度.     

锡基钙钛矿的研究进展及其在发光二极管中的应用

卤化铅钙钛矿由于具有高吸收系数、高载流子迁移率、高缺陷容忍度和高光致发光效率等优越的光电子性能,近年来引起了人们的广泛关注.然而,可能阻碍其商业应用的关键是铅元素的存在引起的毒性问题.为了解决这一毒性问题,谨慎而有策略地用其他无毒候选元素替代Pb2+是一个很有前途的方向.锡具有和铅相似的结构和性质,是目前最有希望替代铅...     

基于改性空穴注入层与复合发光层的高效钙钛矿发光二极管

有机金属卤化钙钛矿作为发射体具有极高的色纯度和极低的成本,但钙钛矿层普遍较差的形貌制约了器件的性能.引入合适的聚合物可有效改善旋涂型钙钛矿薄膜的均匀性.本文引入聚(4-苯乙烯磺酸盐)(PSS)改性的聚(3,4-乙撑二氧噻吩):PSS(PEDOT:PSS)作为空穴注入层(HIL),结合一步旋涂制备的三溴化铅甲基胺(MAPbBr3)和聚(环氧乙烷)(PEO)复合膜作为发光层,制备了高效绿光钙钛矿发光二极管.其中,PSS增加了PEDOT:PSS功函数,降低了其与钙钛矿发光层间的注入势垒;而掺杂PEO的钙钛矿膜致密且均匀,覆盖率可以达到100%.基于改性的空穴注入层和复合发光层,我们最终获得了最大亮度为2476 cd·m^–2、最大电流效率为7.6 cd·A^–1的高效钙钛矿发光二极管.     

Improvement of Photoluminescence of Perovskite CH_3NH_3Pb I_3 by Adding Additional CH_3NH_3I during Grinding

The organic-inorganic hybrid perovskite CH_3NH_3PbI_3 has been a good candidate for many optoelectronic applications such as light-emitting diodes due to its unique properties.Optimizing the optical properties of the CH_3NH_3PbI_3 material to improve the device performance is a hot topic.Herein,a new strategy is proposed to enhance the light emission of CH_3NH_3PbI_3 phosphor effectively.By adding the reactant CH_3NH_3I powder in an appropriate proportion and simply grinding,the emission intensity of CH_3NH_3PbI_3 is greatly improved.The advantages of the proposed method are swiftness,simplicity and reproducibility,and no requirement for a complex organic ligand.The mechanism of this phenomenon is revealed by x-ray diffraction,scanning electron microscopy,energy dispersive spectroscopy,photoluminescence,and temperature-dependent photoluminescence.This study offers a unique insight for optimizing the optical properties of halide perovskite materials.     

Photodetectors based on inorganic halide perovskites:Materials and devices

The newly emerging metal halide perovskites have attracted considerable attention due to their exceptional optoelectronic properties. This upsurge was initially driven when the power conversion efficiency of perovskite-based photovoltaic devices exceeded 23%. Due to their optoelectronic properties, perovskite materials have also been used in light-emitting diodes, photodetectors, lasers, and memory devices. This study comprehensively discusses the recent progress of allinorganic perovskite-based photodetectors, focusing on their structures, morphologies of their constituent materials, and diverse device architectures that improve the performance metrics of these photodetectors. A brief outlook, highlighting the main existing problems, possible solutions to these problems, and future development directions, is also provided herein.     

MAPbI3-xBrx钙钛矿薄膜中溴梯度对界面电荷转移的促进作用

混合卤素钙钛矿由于具有优异的光物理性质成为了光电子领域应用中的明星材料. 因此,钙钛矿材料中光生载流子动力学的探究和调控对于进一步提升材料的性能具有重要意义. 本文通过表面离子交换法制备了具有溴梯度的MAPbI_3-xBr_x钙钛矿薄膜,并对其内部载流子传输及界面电荷转移动力学过程进行了系统的研究. 在MAPbI_3-xBr_x薄膜中,溴离子梯度分布所导致的能带梯度能有效促进光生空穴在薄膜内部的传输过程及在界面的提取过程. 同时,由于卤素离子交换的后处理方法对薄膜表面起到了修饰作用,薄膜界面处的本征电子转移速率也得到了显著的提升. 研究表明,在通过表面后处理方法制备的混合卤素钙钛矿薄膜中,有可能同时实现界面电子和空穴转移速率的提升,这对于进一步提升钙钛矿太阳能电池的能量转换效率具有一定的启发作用.     

基于石墨烯-钙钛矿量子点场效应晶体管的光电探测器

以等离子增强化学气相沉积法制备的石墨烯作为导电沟道材料,将其与无机CsPbI_3钙钛矿量子点结合,设计并制备了石墨烯-钙钛矿量子点场效应晶体管光电探测器.研究和分析了石墨烯作为场效应晶体管的电学特性及其与钙钛矿量子点结合作为光电探测器的光电特性.结果表明,石墨烯在场效应晶体管中表现出良好的电学性质,其与钙钛矿量子点的结合对波长为400 nm的光辐射具有明显的光响应,在光强为12μW时器件光生电流最大为64μA,响应率达6.4 A·W~(-1),对应的光电导增益和探测率分别为3.7×10~4,6×10~7Jones(1 Jones=1 cm·Hz~(1/2)·W~(-1)).     

蒸汽辅助溶液过程制备钙钛矿材料及钙钛矿太阳能电池

有机无机杂化钙钛矿材料被广泛应用于光电器件领域,特别是其作为太阳能电池的吸光材料,受到学术界和工业界越来越多的关注。钙钛矿太阳能电池的产业化进程正在进行中,而在进一步降低制备成本、提高电池转换效率的同时,研究出一种操作简单且可重复性高的制备钙钛矿薄膜的技术具有十分重要的意义。与其他传统的溶液处理方法不同,蒸汽辅助溶液过程(VASP)处理法避免了薄膜在生长过程中溶解以及溶剂化作用,抑制了晶核的形成,使薄膜快速重组,获得致密的高质量钙钛矿薄膜。目前报道,基于此薄膜制备的平面结构钙钛矿太阳能电池转换效率高达16.8%。本文综述了低温(150℃)VASP法制备的钙钛矿薄膜及光伏器件的相关研究进展,并对该技术的产业化前景做了展望。VASP制备过程简单、薄膜性能优异且可重复性高,为进一步制备大面积、高质量薄膜提供了可能。     

Recent progress in all-inorganic metal halide nanostructured perovskites: Materials design,optical properties,and application

Low-dimensional all-inorganic metal halide perovskite (AIMHP) materials, as a new class of nanomaterials, hold great promise for various optoelectronic devices. In the past few years, tremendous progress has been achieved in the development of efficient and stable AIMHP nanomaterials for optical property studies and related applications. Here, we offer a critical overview on the unique merits and the state-of-the-art design of AIMHP using different composition strategies. Then, the effects of material compositions, dimensionality, morphologies and structures on optical properties are summarized. We also comprehensively present recent advances in the development AIMHP nanomaterials for practical applications including solar cells, light-emitting diodes, lasers and photodetectors. Lastly, the critical challenges and future opportunities in this emerging field are highlighted.     

Surface polished of bulk methylammonium lead tribromide single crystal

Organic-inorganic halide perovskite materials have been demonstrated with wide applications in optoelectronics and ionization radiation detection. For bulk as-grown crystals, the existence of surface cracks and defects can significantly increase charges recombination and reduce the performance of the device. Herein, we polished the crystal surfaces with both mechanical and chemical mechanical methods at room temperature. After been chemical-mechanical polished, the crystal surface with root mean square roughness about 0.5 nm was obtained. Optical transmission and photoluminescence spectra indicate that chemical mechanical polishing technology can effectively reduce the density of crystal surface defects. The achieved low leakage current density on the surface and bulk crystal is 0.05 nA mm⁻² and 0.07 nA mm⁻², respectively. Furthermore, the current-voltage curve under visible photons and X-ray photons reveals that surface polishing treatment can suppress the charges recombination and increase the charges transportation.     

A field-effect WSe2/Si heterojunction diode

It is significant to develop a heterogeneous integration technology to promote the application of two-dimensional (2D) materials in silicon roadmap. In this paper, we reported a field-effect WSe₂/Si heterojunction diode based on ambipolar 2D WSe₂ and silicon on insulator (SOI). Our results indicate that the device exhibits a p-n diode behavior with a rectifying ratio of ～ 300 and an ideality factor of 1.37. As a photodetector, it has optoelectronic properties with a response time of 0.13 ms, responsivity of 0.045 A/W, detectivity of 4.5×10¹⁰ Jones and external quantum efficiency (EQE) of 8.9 %. Due to the ambipolar behavior of the WSe₂, the rectifying and optoelectronic properties of the heterojunction diode can be modulated by the gate electrical field, enabling various potential applications such as logic optoelectronic devices and neuromorphic optoelectronic devices for in-sensor computing circuits. Thanks to the process based on the mature SOI technique, our field-effect heterojunction diode should have obvious advantages in device isolation and integration.     

Metal halide perovskite photodetectors: Material features and device engineering

In recent years, the rapid progress of metal halide perovskite solar cells has been witnessed by the rocketing power conversion efficiency. In addition, perovskites have opened up a great opportunity for high performance photodetectors(PDs), due to their attractive optical and electrical properties. This review summarizes the latest progress of perovskitebased PDs, aiming to give a comprehensive understanding of the material design and device engineering in perovskite PDs.To begin with, the performance parameters and device configurations of perovskite PDs are introduced, which are the basis for the next discussion. Next, various PDs based on perovskites in different morphologies are discussed from two aspects:the preparation method, and device performance. Then, several device engineering strategies to enhance the performance of perovskite-based PDs are highlighted, followed by the introduction of flexible and narrow-band perovskite PDs. Finally,key issues and major challenges of perovskite PDs that need to be addressed in the future are outlined.     

Activated carbon as back contact for HTM-free mixed cation perovskite solar cell

Carbon materials have potential applications in perovskite solar cell because of their excellent electronic properties and low cost. In this paper, we report, for the first time, activated carbon as a back contact for hole transport layer-free mixed halide perovskite solar cells. The ability of activated carbon to form conducting chain-like structure when dispersed in a polymeric solution makes it a possible candidate for back contact. A composite of activated carbon and PEMA was optimized with varying concentration. Mixed cation was used as a perovskite absorber and was analysed for its structural and optical properties. The fabricated devices were studied for their electrical performance. They were also subjected to stability study and showed promising results.     

湿度环境下钙钛矿太阳能电池薄膜微结构演化的同步辐射原位实时研究

环境湿度对有机-无机杂化钙钛矿薄膜太阳能电池稳定性有着相当重要的影响,在湿度环境下原位实时观测钙钛矿薄膜微结构的演化有助于揭示湿度导致的器件性能衰减的微观机理.本文基于上海光源X射线衍射线站,建立了一套湿度可调可控的原位X射线衍射实验装置用以实时观测湿度环境下钙钛矿薄膜的微结构演化.在相对湿度为60%±2%的环境中,采用原位同步辐射掠入射X射线衍射发现在钙钛矿薄膜暴露在湿度环境的最初阶段,其(110)衍射峰附近逐渐出现了中间相结构,应该是来源于部分钙钛矿晶体结构的逐渐分解所形成的钙钛矿多相结构;同时,紫外可见吸收光谱实验表明,经环境湿度处理后的薄膜吸收有所降低,尤其是在约770 nm处吸收台阶发生蓝移,在一定程度上反映出钙钛矿晶体结构的减少或结晶性变弱;扫描电子显微镜结果进一步显示,湿度实验后薄膜形貌的均匀性明显变差,覆盖率降低、孔洞变大及晶界变明显;采用环境湿度实验前后的钙钛矿薄膜上制备的太阳能电池J-V性能测试结果显示,器件的填充因子和光电转换效率均由于环境湿度处理降低了30%以上.因此,同步辐射原位实验观测清晰地揭示了器件性能与钙钛矿薄膜形貌以及微结构演化的密切关联,为理解有机-无机杂化的钙钛矿薄膜的降解微观机理提供了实验依据和指导.     

Impeding anion exchange to improve composition stability of CsPbX_3(X= Cl,Br) nanocrystals through facilely fabricated Cs_4Pb_6 shell

Inorganic lead halide perovskite nanocrystals(NCs) with superior photoelectric properties are expected to have excellent performance in many fields. However, the anion exchange changes their features and is unfavorable for their applications in many fields. Hence, impeding anion exchange is important for improving the composition stability of inorganic lead halide perovskite NCs. Herein, CsPb X_3(X = Cl, Br) NCs are coated with Cs_4PbX_6 shell to impede anion exchange and reduce anion mobility. The Cs_4PbX_6 shell is facily fabricated on CsPbX_3 NCs through high temperature injection method.Anion exchange experiments demonstrate that the Cs_4 PbX_6 shell completely encapsulates CsPbX_3 NCs and greatly improves the composition stability of CsPbX_3 NCs. Moreover, our work also sheds light on the potential design approaches of various heterostructures to expand the application of CsPbM_3(M = Cl, Br, I) NCs.