Substrate‐Dependent Spin–Orbit Coupling in Hybrid Perovskite Thin Films

Solution‐processing hybrid metal halide perovskites are promising materials for developing flexible thin‐film devices. This work reports the substrate effects on the spin–orbit coupling (SOC) in perovskite films through thermal expansion under thermal annealing. X‐ray diffraction (XRD) measurements show that using a flexible polyethylene naphthalate (PEN) substrate introduces a smaller mechanical strain in perovskite MAPbI_3?xCl_x films, as compared to conventional glass substrates. Interestingly, the linear/circular photoexcitation‐modulated photocurrent studies find that decreasing mechanical strain gives rise to a weaker orbit–orbit interaction toward decreasing the SOC in the MAPbI_3?xCl_x films prepared on flexible PEN substrates relative to rigid glass substrates. Simultaneously, decreasing the mechanical strain causes a reduction in the internal magnetic parameter inside the MAPbI_3?xCl_x films, providing further evidence to show that introducing mechanical strain can affect the SOC in hybrid perovskite films upon using flexible substrates toward developing flexible perovskite thin‐film devices. Furthermore, thermal admittance spectroscopy indicates that the trap states are increased in the perovskite films prepared on flexible PEN substrates as compared to glass substrates. Consequently, PEN and rigid glass substrates lead to shorter and longer photoluminescence lifetimes, respectively. Clearly, these findings provide an insightful understanding on substrate effects on optoelectronic properties in flexible perovskite thin‐film devices.     

Impact of Processing on Structural and Compositional Evolution in Mixed Metal Halide Perovskites during Film Formation

Understanding crystallization processes and their pathways in metal‐halide perovskites is of crucial importance as this strongly affects the film microstructure, its stability, and device performance. While many approaches are developed to control perovskite formation, the mechanisms of film formation are still poorly known. Using time‐resolved in situ grazing incidence wide‐angle X‐ray scattering, the film formation of perovskites is investigated with average stoichiometry Cs_0.15FA_0.85PbI₃, where FA is formamidinium, using the popular antisolvent dropping and gas jet treatments and this is contrasted with untreated films. i) The crystallization pathways during spin coating, ii) the subsequent postdeposition thermal annealing, and iii) crystallization during blade coating are studied. The findings reveal that the formation of a nonperovskite FAPbI₃ phase during spin coating is initially dominant regardless of the processing and that the processing treatment (e.g., antisolvent dropping, gas jet) has a significant impact on the as‐cast film structure and affects the phase evolution during subsequent thermal treatment. It is shown that blade coating can be used to overcome the nonperovskite phase formation via solvothermal direct crystallization of perovskite phase. This work shows how real‐time investigation of perovskite formation can help to establish processing–microstructure–functionality relationships.     

Numerical simulation of thermal wave propagation during laser processing of thin films

A numerical model is developed to represent the thermal wave propagation during ultrashort pulsed laser processing of thin films. The model developed is based on the solution of non-Fourier heat conduction problem with temperature and thermal flux delays using discontinuous finite-element method. The mathematical formulation is described and computational procedures are given. The computer model is validated using the analytical solution for one-dimensional (1-D) thermal wave equations. Numerical simulations are performed to study the thermal wave propagation in a GaAs thin film exposed to ultrashort laser pulses. A wavelike behavior of the thermal signal propagation is observed, and the diffusive effect of the time relaxation in the temperature gradient is calculated and discussed. The thermal behavior of thin films under laser radiation is also studied as a function of various process parameters including pulse duration, laser pulse shapes and characteristic times of heat fluxes.     

A Simple Way to Simultaneously Release the Interface Stress and Realize the Inner Encapsulation for Highly Efficient and Stable Perovskite Solar Cells

The mixed halide perovskites have become famous for their outstanding photoelectric conversion efficiency among new‐generation solar cells. Unfortunately, for perovskites, little effort is focused on stress engineering, which should be emphasized for highly efficient solar cells like GaAs. Herein, polystyrene (PS) is introduced into the perovskite solar cells as the buffer layer between the SnO₂ and perovskite, which can release the residual stress in the perovskite during annealing because of its low glass transition temperature. The stress‐free perovskite has less recombination, larger lattices, and a lower ion migration tendency, which significantly improves the cell's efficiency and device stability. Furthermore, the so‐called inner‐encapsulated perovskite solar cells are fabricated with another PS capping layer on the top of perovskite. As high as a 21.89% photoelectric conversion efficiency (PCE) with a steady‐state PCE of 21.5% is achieved, suggesting that the stress‐free cell can retain almost 97% of its initial efficiency after 5 days of “day cycle” stability testing.     

Efficient Cesium Lead Halide Perovskite Solar Cells through Alternative Thousand‐Layer Rapid Deposition

The novel growth of cesium lead halide perovskite thin films, which are prepared through thousand‐layer rapid alternative deposition, is performed by developing an active perovskite film consisting of a layer‐by‐layer structure. This method is considerably more difficult to be implemented from the solution process. The obtained thin film morphology and characteristics are distinguished from that of the traditional a few layers and two‐material codeposition. These alternative deposited perovskites are integrated with vacuum‐deposited carrier‐transporting layers and electrodes, and all vacuum‐sublimed perovskite solar cells exhibit an outstanding power conversion efficiency of 13.0%. The use of these devices for environmental light energy harvesting provides a power conversion efficiency of 33.9% under fluorescent light illumination of 1000 lux.     

Precursor Solution Annealing Forms Cubic‐Phase Perovskite and Improves Humidity Resistance of Solar Cells

Solar cells with light‐absorbing layers comprising organometal halide perovskites have recently exceeded 22% efficiency. Despite high power‐conversion efficiencies, the stability of these devices, particularly when exposed to humidity and oxygen, remains poor. In the current study, a pathway to increase the stability of methylammonium lead iodide (CH₃NH₃PbI₃) based solar cells towards humidity is demonstrated, while maintaining the simplicity and solution‐processability of the active layers. Thermal annealing of the precursor solution prior to deposition induces the formation of cubic‐phase perovskite films in the solid state at room temperature. The experiments demonstrate that this improved ambient stability is correlated with the presence of the cubic phase at device operating temperatures, with the cubic phase resisting the formation of perovskite monohydrate—a pathway of degradation in conventionally processed perovskite thin films—on exposure to humidity.     

Recent Advances and Perspectives on Powder-Based Halide Perovskite Film Processing

Halide perovskites have undergone an impressive development and could be used in a wide range of optoelectronic devices, where some of them are already at the edge of commercialization, e.g., perovskite solar cells. Recently, interest in perovskites in powder form has increased, as for example, they are found to exhibit high stability and allow for easy production of large quantities. Accordingly, also the topic of processing thin and thick films on the basis of perovskite powders is currently gaining momentum. Here, perovskite powder can form the basis for both, typical wet and solvent-based processing approaches, as well as for dry processes. In this Progress Report, the recent developments of halide perovskites in powder form and of film processing approaches are summarized that are based on them. The advantages and opportunities of the different processing methods are highlighted, but their individual drawbacks and limitations are also discussed. Prospects are also pointed out and possible steps necessary to unlock the full potential of powder-based processing methods for producing high quality thick and thin perovskite layers in the future are discussed.     

退火对用PLD法制备ZnO薄膜的发光影响

用脉冲激光沉积(PLD)方法在Si(111)和蓝宝石衬底上制备的氧化锌薄膜,在不同的退火温度和不同的退火氛围中进行了退火处理.退火温度及退火氛围对ZnO薄膜的结构和发光特性的影响用X射线衍射(XRD)谱和光致发光谱进行了表征.实验结果表明,随着退火温度的提高,ZnO薄膜的压应力减小,并向张应力转化.在不同的退火温度退火...     

Room‐Temperature Partial Conversion of α‐FAPbI3 Perovskite Phase via PbI2 Solvation Enables High‐Performance Solar Cells

The two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI₃ hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI₃, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI₃, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI₂ into the α‐FAPbI₃ perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI₂ precursor from its different states are compared. α‐FAPbI₃ forms spontaneously and efficiently at room temperature from P₂ (ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI₂) to 17.23(±0.28)% (from solvated PbI₂) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA⁺ cation without the need for Cs⁺ or mixed halide formulation.     

Effects of annealing technique and TiO2 seed layer on the phase composition of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 film

The lead magnesium niobate–lead titanate (PMN–PT) thin films with and without the TiO₂ seed layer were prepared by a pulsed laser deposition (PLD) deposited on Pt/Ti/SiO₂/Si substrates. The films were treated by two-step annealing and normal annealing with rapid thermal annealing (RTA). The effects of two-step annealing and the TiO₂ seed layer on the phase composition of PMN–PT films were studied. The results show that the PMN–PT film with TiO₂ seed layer can gain a pure perovskite phase with a high (1 0 0) preferential orientation after the two-step annealing technique.     

Cooling,Scattering, and Recombination—The Role of the Material Quality for the Physics of Tin Halide Perovskites

Tin‐based perovskites have long remained a side topic in current perovskite optoelectronic research. With the recent efficiency improvement in thin film solar cells and the observation of a long hot carrier cooling time in formamidinium tin iodide (FASnI₃), a thorough understanding of the material's photophysics becomes a pressing matter. Since pronounced background doping can easily obscure the actual material properties, it is of paramount importance to understand how different processing conditions affect the observed behavior. Using photoluminescence spectroscopy, thin films of FASnI₃ fabricated through different protocols are therefore investigated. It is shown that hot carrier relaxation occurs much faster in highly p‐doped films due to carrier–carrier scattering. From high quality thin films, the longitudinal optical phonon energy and the electron–phonon coupling constant are extracted, which are fundamental to understanding carrier cooling. Importantly, high quality films allow for the observation of a previously unreported state of microsecond lifetime at lower energy in FASnI₃, that has important consequences for the discussion of long lived emission in the field of metal halide perovskites.     

The effect of pulsed laser annealing on the nickel silicide formation

The pulsed laser annealing (PLA) is used to assist nickel silicide transformation for Schottky barrier height reduction and tensile strain enhancement and the effect of different laser power are investigated. In this report, a two-step annealing process which combine the conventional rapid thermal annealing with pulsed laser annealing is proposed to achieve a smooth silicon-rich NiSi_x interfacial layer on (1 0 0) silicon. With optimized laser energy, a 0.2 eV Schottky barrier height (SBH) modulation is observed from Schottky diode electrical characterization. Furthermore, PLA provides sufficient effective temperature during silicidation which also lead to increased tensile stress of silicide film than the two-step RTA silicide is also investigated. The SBH modulation and tensile stress enhancement benefits of PLA silicidation are considered as an alternative to the conventional rapid thermal annealing for ultra-scaled devices performance enhancement.     

脉冲激光沉积法制备PZT铁电薄膜及衬底温度对膜的影响

采用脉冲激光沉积法在Si(10 0 )衬底上制备了Pb(Zr0 .52 Ti0 .4 8)O3 铁电薄膜 ,并用X射线衍射 (XRD) ,扫描电镜 (SEM )对其结构、形貌以及结构随沉积时衬底温度的变化进行了研究。由脉冲激光制备薄膜的机制出发 ,从PbO ,ZrO2 和TiO2 熔融体的化学反应及应力造成能量释放引起的相变两方面分析了铅基铁电薄膜制备时衬底温度的影响。     

Novel Direct Nanopatterning Approach to Fabricate Periodically Nanostructured Perovskite for Optoelectronic Applications

While indirectly patterned organic–inorganic hybrid perovskite nanostructures have been extensively studied for use in perovskite optoelectronic devices, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high‐temperature environments. Here, a simple and low‐cost approach is proposed to directly pattern perovskite solid‐state films into periodic nanostructures. The approach is basically perovskite recrystallization through phase transformation with the presence of a periodic mold on an as‐prepared solid‐state perovskite film. Interestingly, this study simultaneously achieves not only periodically patterned perovskite nanostructures but also better crystallized perovskites and improved optical properties, as compared to its thin film counterpart. The improved optical properties can be attributed to the light extraction and increased spontaneous emission rate of perovskite gratings. By fabricating light‐emitting diodes using the periodic perovskite nanostructure as the emission layers, approximately twofold higher radiance and lower threshold than the reference planar devices are achieved. This work opens up a new and simple way to fabricate highly crystalline and large‐area perovskite periodic nanostructures for low‐cost production of high‐performance optoelectronic devices.     

Tailoring the Fabrication Method of Dion–Jacobson 2D Halide Perovskites toward Highly Crystalline and Oriented Films

Halide perovskites are potential next-generation optoelectronic devices. However, the film quality of this charming material fabricated by the conventional spin-coating method is far from satisfactory, significantly affecting the optoelectronic devices' performance. Here, one facile slow-evaporating solvent (SE) method is demonstrated to synthesize high-quality organic–inorganic halide perovskite films. Compared with the conventional spin coating method, the films fabricated by this SE method show much higher crystallinity, oriented lattice, smoother surface morphology, and lower trap density. Besides, the photodetector manufactured by the SE method-based film also performs much better than the ones by the spin-coating method. Importantly, this universal method can be applied to different organic–inorganic halide perovskites, such as Dion–Jacobson (DJ) type and Ruddlesden–Popper type 2D halide perovskites and conventional 3D halide perovskites. This work gives an effective solution to improve the quality of the DJ-type halide perovskites, which endows the halide perovskites with a more practical chance to be commercialized cosmically.     

激光脉宽对光学薄膜元件热损伤的影响

纳秒量级及以下脉宽激光致光学薄膜元件的损伤研究持续了几十年,但纳秒量级以上脉宽却很少提及。因此,针对10 ns~1 ms量级区间不同脉宽激光辐照光学薄膜元件产生的热损伤进行了研究,计算了高反膜、增透膜和干涉滤光片三种典型光学薄膜元件的温度场分布,并分析了其激光热损伤特性。结果表明,对于长脉宽激光,热扩散深度大,薄膜损伤的电场效应被削弱,热传导效应在损伤中占据主导地位,损伤可至基底;短脉宽激光损伤对薄膜内部的电场分布更为敏感,损伤发生在温度最高值附近的膜层区域。进而开展了10 ns与1 ms脉宽激光致光学薄膜元件的损伤实验,损伤阈值及形貌特征与温度场计算结果显示的热损伤特性相符。     

脉冲激光辐照金属板温度场应力场数值分析

为了研究脉冲激光加热金属板的温度场和应力场的特点,基于弹塑性力学理论,采用有限元分析方法,对脉冲激光扫描过程中金属板的温度场和应力场进行了3维数值模拟,得到了温度场与应力场在时间和空间上的分布和变化规律。结果表明,在脉冲激光扫描加热作用下,金属表面发生多次熔化和凝固,温度时间曲线呈锯齿形;重熔区域应力场变化剧烈,随间歇的激光脉冲发生强烈的拉-压应力波动;金属基体冷却后在重熔区域留有高值残余拉应力,纵向应力达799MPa,横向应力达700MPa。     

Metal Halide Perovskite Arrays: From Construction to Optoelectronic Applications

Inorganic semiconductor arrays revolutionize many areas of electronics, optoelectronics with the properties of multifunctionality and large-scale integration. Metal halide perovskites are emerging as candidates for next-generation optoelectronic devices due to their excellent optoelectronic properties, ease of processing, and compatibility with flexible substrates. To date, a series of patterning technologies have been applied to perovskites to realize array configurations and nano/microstructured surfaces to further improve device performances. Herein, various construction methods for perovskite crystal or thin film arrays are summarized. The optoelectronic applications of the perovskite arrays are also discussed, in particular, for photodetectors, light-emitting diodes, lasers, and nanogratings.     

Incubating High-Quality Perovskite Film via Facial Mask Technique for Efficient and Stable Solar Cells

High-performance perovskite film with superior internal and surface qualities is critical for perovskite solar cells (PSCs) but hardly achievable due to the rapid crystallization rate of perovskite itself. Herein, a novel technique by in situ manipulating perovskite crystal growth and modifying the surface properties is developed using organic passivating agent-assisted polydimethylsiloxane membrane as a facial mask (FM) of perovskites. By placing the perovskite-precursor films with their faces toward the designed FM during thermal annealing, a favorable microenvironment is constructed for incubating high-quality perovskite films with smooth surface, enhanced vertical orientation of (100) plane, and well-adjusted interfacial energy levels. With this versatile FM incubation technique, efficient PSCs for both methylammonium (MA)-based and formamidinium (FA)-MA-Cs mixed perovskite systems are facilely fabricated, delivering excellent humidity/thermal stabilities and promising efficiencies up to 21.4% with an improved open-circuit voltage of 1.15 V in MA-based devices. This study not only provides a facile and efficient approach to rationally manage the perovskite growth process, but also reveals the fundamental characteristics of high-quality perovskite films comprehensively for the construction of efficient and stable PSCs.     

钛酸铋薄膜的室温脉冲激光沉积研究

在室温下,采用脉冲激光沉积（ＰＬＤ）技术在７．６２ｃｍＰｔ／Ｔｉ／ＳｉＯ２／Ｓｉ（１００）衬底上制备了钛酸铋（Ｂｉ４Ｔｉ３Ｏ１２）薄膜。Ｂｉ４Ｔｉ３Ｏ１２薄膜的厚度和组分均匀性采用卢瑟福背散射（ＲＢＳ）和扩展电阻技术（ＳＲＰ）来分析、表征;采用Ｘ射线衍射（ＸＲＤ）技术研究了薄膜的退火特性。研究发现单独用常规退火或快速退火热处理的Ｂｉ４Ｔｉ３Ｏ１２薄膜中较容易出现Ｂｉ２Ｔｉ２Ｏ７杂相;而采用常规退火和快速退火相结合的方法,较好地解决了杂相出现的问题,得到相结构和结晶性完好的Ｂｉ４Ｔｉ３Ｏ１２薄膜。透射电子显微镜实验和扩展电阻实验表明,室温下制备的Ｂｉ４Ｔｉ３Ｏ１２薄膜具有良好的表面和界面特性。