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Tin dioxide (SnO2) has been demonstrated as one of the promising electron transport layers for high-efficiency perovskite solar cells (PSCs). However, scalable fabrication of SnO2 films with uniform coverage, desirable thickness and a low defect density in perovskite solar modules (PSMs) is still challenging. Here, we report preparation of high-quality large-area SnO2 films by chemical bath deposition (CBD) with the addition of KMnO4. The strong oxidizing nature of KMnO4 promotes the conversion from Sn(II) to Sn(VI), leading to reduced trap defects and a higher carrier mobility of SnO2. In addition, K ions diffuse into the perovskite film resulting in larger grain sizes, passivated grain boundaries, and reduced hysteresis of PSCs. Furthermore, Mn ion doping improves both the crystallinity and the phase stability of the perovskite film. Such a multifunctional interface engineering strategy enabled us to achieve a power conversion efficiency (PCE) of 21.70% with less hysteresis for lab-scale PSCs. Using this method, we also fabricated 5 × 5 and 10 × 10 cm2 PSMs, which showed PCEs of 15.62% and 11.80% (active area PCEs are 17.26% and 13.72%), respectively. For the encapsulated 5 × 5 cm2 PSM, we obtained a T80 operation lifetime (the lifespan during which the solar module PCE drops to 80% of its initial value) exceeding 1000 h in ambient condition.

Two-dimensional Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) phase perovskites are promising alternatives to fabricate blue perovskite light-emitting diodes (PeLEDs) due to their strong quantum/dielectric confinement. While the RP phase perovskites have been widely used as emitter layers in blue PeLEDs, the DJ phase perovskites, possessing better structural stability and charge transfer property, have received little attention. Here, we report the use of DJ phase perovskites for fabricating efficient sky-blue PeLEDs. Organic diamine propane-1,3-diammonium cations were first incorporated into CsPbBr3 to prepare DJ phase perovskites. RbBr was further incorporated as a passivation agent to eliminate traps. It is found that diamine cations and RbBr are interdependent in terms of increasing the utilization of charges. Radiative recombination was enhanced, effectively benefiting from the synergetic confinement and passivation effects. The photoluminescence quantum yield approached 70%. Finally, the fabricated PeLEDs achieved an external quantum efficiency of 8.5% with an emission peak at 490 nm.

With the development of human society, the problems of environmental deterioration and energy shortage have become increasingly prominent. In order to solve these problems, metal halide perovskite solar cells (PSCs) stand out because of their excellent properties (i.e., high optical absorption coefficient, long carrier lifetime and carrier diffusion length, adjustable band gap) and have been widely studied. PSCs with low cost, high power conversion efficiency and high stability are the future development trend. The quality of perovskite film is essential for fabricating PSCs with high performance. To provide a full picture of realizing high performance PSCs, this review focuses on the strategies for preparing high quality perovskite films (including antisolvent, Lewis acid-base, additive engineering, scaleable fabrication, strain engineering and band gap adjustment), and therefore to fabricate high performance PSCs and to accelerate the commercialization.

The incorporation of a certain amount of Cl ions into methylammonium lead iodide (MAPbI3) perovskite films and how these incorporated Cl ions affect the structural and electronic properties of these films have been an intensively studied topic. In this study, we comprehensively investigated Cl incorporation in MAPbI3 at the atomic scale by a combined study of scanning tunneling microscopy, X-ray photoelectron spectroscopy, ultraviolet and inverse photoemission spectroscopy, density functional theory and molecular dynamics calculations. At a Cl concentration of 14.8 ± 0.6%, scanning tunneling microscopy images confirm the incorporation of Cl ions on the MAPbI3 surface, which also corresponds to the highest surface stability of MAPbI3 found from the viewpoint of both thermodynamics and kinetics by density functional theory and molecular dynamics calculations. Our results show that the Cl concentration is crucial to the surface bandgap and stability of MAPbI3.

All-inorganic α-CsPbBrxI3-x perovskites featuring nano-sized crystallites show great potential for pure-red light-emitting diode (LED) applications. Currently, the CsPbBrxI3–x LEDs based on nano-sized α-CsPbBrxI3-x crystallites have been fabricated mainly via the classical colloidal route including a tedious procedure of nanocrystal synthesis, purification, ligand or anion exchange, film casting, etc. With the usually adopted conventional LED device structure, only high turn-on voltages (> 2.7) have been achieved for CsPbBrxI3-x LEDs. Moreover, this mix-halide system may suffer from severe spectra-shift under bias. In this report, CsPbBrxI3-x thin films featuring nano-sized crystallites are prepared by incorporating multiple ammonium ligands in a one-step spin-coating route. The multiple ammonium ligands constrain the growth of CsPbBrxI3-x nanograins. Such CsPbBrxI3-x thin films benefit from quantum confinement. The corresponding CsPbBrxI3-x LEDs, adopting a conventional LED structure of indium-doped tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/CsPbBrxI3-x/[6, 6]-phenyl C61 butyric acid methyl ester (PCBM)/bathocuproine (BCP)/Al, emit pure-red color at Commission Internationale de l’eclairage (CIE) coordinates of (0.709, 0.290), (0.711, 0.289), etc., which represent the highest color-purity for reported pure-red perovskite LEDs and meet the Rec. 2020 requirement at CIE (0.708, 0.292) very well. The CsPbBrxI3-x LED shows a low turn-on voltage of 1.6 V, maximum external quantum efficiency of 8.94%, high luminance of 2,859 cdm−2, and good color stability under bias.

The upscaling of perovskite solar cells to module scale and long-term stability have been recognized as the most important challenges for the commercialization of this emerging photovoltaic technology. In a perovskite solar module, each interface within the device contributes to the efficiency and stability of the module. Here, we employed a holistic interface stabilization strategy by modifying all the relevant layers and interfaces, namely the perovskite layer, charge transporting layers and device encapsulation, to improve the efficiency and stability of perovskite solar modules. The treatments were selected for their compatibility with low-temperature scalable processing and the module scribing steps. Our unencapsulated perovskite solar modules achieved a reverse-scan efficiency of 16.6% for a designated area of 22.4 cm2. The encapsulated perovskite solar modules, which show efficiencies similar to the unencapsulated one, retained approximately 86% of the initial performance after continuous operation for 2,000 h under AM1.5G light illumination, which translates into a T90 lifetime (the time over which the device efficiency reduces to 90% of its initial value) of 1,570 h and an estimated T80 lifetime (the time over which the device efficiency reduces to 80% of its initial value) of 2,680 h. The upscaling of layer treatments and processing that afford high efficiency and stability in small-area perovskite solar cells remains challenging. Liu et al. show how the efficiency and stability of perovskite modules can be improved using an integrated approach to interface and layer engineering.

The booming growth of organic-inorganic hybrid lead halide perovskite solar cells have made this promising photovoltaic technology to leap towards commercialization. One of the most important issues for the evolution from research to practical application of this technology is to achieve high-throughput manufacturing of large-scale perovskite solar modules. In particular, realization of scalable fabrication of large-area perovskite films is one of the essential steps. During the past ten years, a great number of approaches have been developed to deposit high quality perovskite films, to which additives are introduced during the fabrication process of perovskite layers in terms of the perovskite grain growth control, defect reduction, stability enhancement, etc. Herein, we first review the recent progress on additives during the fabrication of large area perovskite films for large scale perovskite solar cells and modules. We then focus on a comprehensive and in-depth understanding of the roles of additives for perovskite grain growth control, defects reduction, and stability enhancement. Further advancement of the scalable fabrication of high-quality perovskite films and solar cells using additives to further develop large area, stable perovskite solar cells are discussed.

Control of forward and inverse reactions between perovskites and precursor materials is key to attaining high-quality perovskite materials. Many techniques focus on synthesizing nanostructured CsPbX3 materials (e.g., nanowires) via a forward reaction (CsX + PbX2 → CsPbX3). However, low solubility of inorganic perovskites and complex phase transition make it difficult to realize the precise control of composition and length of nanowires using the conventional forward approach. Herein, we report the self-assembly inverse growth of CsPbBr3 micronanowires (MWs) (CsPb2Br5 → CsPbBr3 + PbBr2↑) by controlling phase transition from CsPb2Br5 to CsPbBr3. The two-dimensional (2D) structure of CsPb2Br5 serves as nucleation sites to induce initial CsPbBr3 MW growth. Also, phase transition allows crystal rearrangement and slows down crystal growth, which facilitates the MW growth of CsPbBr3 crystals along the 2D planes of CsPb2Br5. A CsPbBr3 MW photodetector constructed based on the inverse growth shows a high responsivity of 6.44 A W–1 and detectivity of ∼1012 Jones. Large grain size, high crystallinity, and large thickness can effectively alleviate decomposition/degradation of perovskites, which leads to storage stability for over 60 days in humid environment (relative humidity = 45%) and operational stability for over 3000 min under illumination (wavelength = 400 nm, light intensity = 20.06 mW cm–2).

In several photovoltaic (PV) technologies, the presence of electronic defects within the semiconductor band gap limit the efficiency, reproducibility, as well as lifetime. Metal halide perovskites (MHPs) have drawn great attention because of their excellent photovoltaic properties that can be achieved even without a very strict film‐growth control processing. Much has been done theoretically in describing the different point defects in MHPs. Herein, we discuss the experimental challenges in thoroughly characterizing the defects in MHPs such as, experimental assignment of the type of defects, defects densities, and the energy positions within the band gap induced by these defects. The second topic of this Review is passivation strategies. Based on a literature survey, the different types of defects that are important to consider and need to be minimized are examined. A complete fundamental understanding of defect nature in MHPs is needed to further improve their optoelectronic functionalities., Watching the defects: Defects play a pivotal role in the overall performance of perovskite solar cells. This Review focuses on central questions of “what defects exist in metal halide perovskites” and “how can one reduce detrimental defects towards high‐performance perovskite solar cells”.

All-inorganic halide perovskites are promising materials for optoelectronic applications. The surface or interface structure of the perovskites plays a crucial role in determining the optoelectronic conversion efficiency, as well as the material stability. A thorough understanding of surface atomic structures of the inorganic perovskites and their contributions to their optoelectronic properties and stability is lacking. Here we show a scanning tunneling microscopy investigation on the atomic and electronic structure of CsPbBr3 perovskite. Two different surface structures with a stripe and an armchair domain are identified, which originates from a complex interplay between Cs cations and Br anions. Our findings are further supported and correlated with density functional theory calculations and photoemission spectroscopy measurements. The stability evaluation of photovoltaic devices indicates a higher stability for CsPbBr3 in comparison with MAPbBr3, which is closely related to the low volatility of Cs from the perovskite surface.

Hybrid chemical vapor deposition (HCVD) has been employed in the fabrication of perovskite solar cells (PSCs) and modules (PSMs), and it shows strong promise for upscalable fabrication. The conventional HCVD process needs a relatively long processing time (e.g., several hours) and the fabricated PSCs often exhibit salient hysteresis, which impedes utilization of this technology for mass production. Herein, we demonstrate a rapid HCVD (RHCVD) fabrication process for PSCs using a rapid thermal process, which not only significantly reduces the deposition time to less than 10 min, but also effectively suppresses hysteresis. This markedly reduced deposition time is comparable to that of solution-coating processes. Furthermore, the shorter processing time inside the furnace reduces the exposure time of the glass/ITO/SnO2 substrates under vacuum, which helps maintain the high quality of the SnO2 electron-transport layer and results in a lower density of gap states. Finally, PSMs with a designated area of 22.4 cm2 fabricated via RHCVD achieved an efficiency of 12.3%, and maintained 90% of the initial value after operation under continuous light illumination for over 800 h.

Highlights Recent progress of efficiency and long-term stability for perovskite solar cells, and the development of perovskite-based tandem solar cells are described. The progress of lead-free perovskite solar cells and their potential for industrial production are discussed in detail. The current status, ongoing challenges, and the future outlooks of perovskite solar cells are highlighted., Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

Atomistic characterization of surface termination and the corresponding mechanical properties of single-crystal methylammonium lead tribromide (MAPbBr3) are performed using combined atomic force microscopy (AFM) measurements and density functional theory (DFT) calculations. A clean MAPbBr3 surface is obtained by in situ cleavage in ultrahigh vacuum at room temperature, and the subsequent AFM measurements of the as-cleaved MAPbBr3 exhibit the coexistence of two different surface terrace types with step height differences corresponding to about half the thickness of a PbI6 octahedron layer. Concurrent friction force microscopy measurements show that the two surfaces result in two distinct friction values. Based on DFT calculations, we attribute the higher-friction and lower-friction surfaces to MABr-terminated flat and PbBr2-terminated vacant surface terminations, respectively. The calculated electronic band structures of the various MABr- and PbBr2-terminated surfaces show that the midgap states are absent, revealing the defect-tolerant nature of the ideal single-crystal MAPbBr3 surfaces.

A series of challenging issues such as field-driven spectral drift for the CsPbClxBr3–x system and mixed phases in quasi-two-dimensional structures still exist when devising blue-emitting perovskites. In this Letter, the CsPbBr3 quantum-dot (QD) system is proposed to overcome these challenges. However, to date, the CsPbBr3 QD films with tunable colors from green to blue still cannot be achieved using existing methods. Herein, a simple one-step spin-coating route incorporated with efficient ligand passivation is developed to realize this goal. The size restriction of CsPbBr3 QDs is enabled by a diammonium ligand, propane-1,3-diammonium bromide (PDAB). A mixed-ligand system of phenethylammonium bromide (PEAB) with PDAB is further explored to enhance their optical performance. The CsPbBr3 QDs experience a second growth process upon controlled air exposure, which is utilized to realize their size control and emission wavelength tunability. The CsPbBr3 QD-based devices exhibit no spectral drift in electroluminescence under voltage bias.

Metal halide-based perovskite solar cells (PSCs) have developed rapidly due to exceptional optoelectronic properties of perovskite materials (such as high optical absorption coefficient, long charge carrier lifetime, long diffusion length, high carrier mobility and tunable bandgaps) and low-cost fabrication processes. The record power conversion efficiency has exceeded 24%, demonstrating the great potential for photovoltaic application. However, the lead toxicity and instability still present as major obstacles for commercialization. In principle, Pb can be replaced with other less-toxic as well as environmentally benign metals, such as Ag, Na, Sn, Ge, Bi, Sb and Ti, to solve the toxicity issue. Replacing methylammonium (MA(+)) or formamidinium (FA(+)) with cesium (Cs+) represents a promising direction to address the instability issue. Herein, we review the recent progress of all-inorganic cesium lead-free halide PSCs. At the end, we outline challenges and future directions.

Perovskite photovoltaic (PV) technology toward commercialization relies on high power conversion efficiency (PCE), long lifetime, and low-toxicity in addition to development of scalable fabrication...

Carbon electrode-based perovskite solar cells (PSCs) with low-cost and long-term stability have been recognized as a competitive candidate toward future practical applications. However, energy leve...

In recent years, the major factors that determine commercialization of perovskite photovoltaic technology have been shifting from solar cell performance to stability, reproducibility, device upscaling and the prevention of lead (Pb) leakage from the module over the device service life. Here we simulate a realistic scenario in which perovskite modules with different encapsulation methods are mechanically damaged by a hail impact (modified FM 44787 standard) and quantitatively measure the Pb leakage rates under a variety of weather conditions. We demonstrate that the encapsulation method based on an epoxy resin reduces the Pb leakage rate by a factor of 375 compared with the encapsulation method based on a glass cover with an ultraviolet-cured resin at the module edges. The greater Pb leakage reduction of the epoxy resin encapsulation is associated with its optimal self-healing characteristics under the operating conditions and with its increased mechanical strength. These findings strongly suggest that perovskite photovoltaic products can be deployed with minimal Pb leakage if appropriate encapsulation is employed. Lead leakage from damaged perovskite solar cells poses a challenge to the deployment of such technology. Here, Jiang, Qiu and co-workers quantify lead leakage caused by a simulated hail impact under a number of weather conditions and show that self-healing encapsulations can effectively reduce it.

The correct identification of all gases released during hybrid perovskite degradation is of great significance to develop strategies to extend the lifespan of any device based on this semiconductor. CH3X (X = Br/I) is a released degradation gas/low boiling point liquid arising from methylammonium (MA+) based perovskites, which has been largely overlooked in the literature focusing on stability of perovskite solar cells. Herein, we present an unambiguous identification of CH3I release using microwave (rotational) spectroscopy. An experimental back-reaction test demonstrates that the well-known CH3NH2/HX degradation route may not be the ultimate degradation pathway of MAPbX3 in thermodynamic closed systems. Meanwhile, the CH3X/NH3 route cannot back-react selectively to MAX formation as occurred for the former back-reaction. Metadynamics calculations uncover the X halide effect on energy barriers for both degradation reactions showing a better stability of Br based perovskite ascribed to two aspects: (i) lower Brönsted–Lowry acidity of HBr compared to HI and (ii) higher nucleophilic character of CH3NH2 compared to NH3. The latter property makes CH3NH2 molecules stay preferentially attached on the electrophilic perovskite surface (Pb2+) during the dynamic simulation instead of being detached as observed for the NH3 molecule.

Grain boundaries in organic–inorganic halide perovskite solar cells (PSCs) have been found to be detrimental to the photovoltaic performance of devices. Here, we develop a unique approach to overcome this problem by modifying the edges of perovskite grain boundaries with flakes of high-mobility two-dimensional (2D) materials via a convenient solution process. A synergistic effect between the 2D flakes and perovskite grain boundaries is observed for the first time, which can significantly enhance the performance of PSCs. We find that the 2D flakes can conduct holes from the grain boundaries to the hole transport layers in PSCs, thereby making hole channels in the grain boundaries of the devices. Hence, 2D flakes with high carrier mobilities and short distances to grain boundaries can induce a more pronounced performance enhancement of the devices. This work presents a cost-effective strategy for improving the performance of PSCs by using high-mobility 2D materials.

Summary With the rapid developments in lead halide perovskite solar cell technology, record-high power conversion efficiencies have been achieved, and significant research efforts have been directed toward stability, which is still a major challenge facing the commercialization of perovskite solar cell technology. In this review article, we review the research progress that has been made on the stability of perovskite solar cells. We start with an analysis of recently reported operational stability profiles of perovskite solar cells. On the basis of the analysis, we determine the solar cell lifetime (i.e., T80 values) and the total amount of energy generated during the lifespan of a perovskite solar cell, from which several trends are inferred. In the subsequent sections, we further examine the instability issues associated with various constituents in a perovskite solar cell and the new methods/strategies that have been developed to solve these issues.

Summary In recent years, metal halide perovskite opens the new era of the photovoltaic field. The highest power conversion efficiency has exceeded 23%. Although most of reported perovskite solar cells (PSCs) were fabricated by solution methods, the vacuum thermal evaporation method has its unique advantages, such as easy controlling of film thickness, compatibility with tandem cell designs, flexibility to tune interfaces, free of solvent, etc. In this paper, we review the development and progress of the vacuum thermal evaporation method for fabricating PSCs.

Besides high efficiency, the stability and reproducibility of perovskite solar cells (PSCs) are also key for their commercialization. Herein, we report a simple perovskite formation method to fabricate perovskite films with thickness over 1 μm in ambient condition on the basis of the fast gas−solid reaction of chlorine-incorporated hydrogen lead triiodide and methylamine gas. The resultant thick and smooth chlorine-incorporated perovskite films exhibit full coverage, improved crystallinity, low surface roughness and low thickness variation. The resultant PSCs achieve an average power conversion efficiency of 19.1 ± 0.4% with good reproducibility. Meanwhile, this method enables an active area efficiency of 15.3% for 5 cm × 5 cm solar modules. The un-encapsulated PSCs exhibit an excellent T80 lifetime exceeding 1600 h under continuous operation conditions in dry nitrogen environment.

Organic field-effect transistors (OFETs) are the most fundamental device units in organic electronics. Interface engineering at the semiconductor/dielectric interface is an effective approach for improving device performance, particularly for enhancing charge transport in conducting channels. Here, we report flat-lying molecular monolayers that exhibit good uniformity and high crystallinity at the semiconductor/dielectric interface, deposited through slow thermal evaporation. Transistor devices achieve high carrier mobility up to 2.80 cm2 V–1 s–1, which represents a remarkably improvement in device performance compared with devices that are completely based on fast-evaporated films. Interfacial flat-lying monolayers benefit charge transport by suppressing the polarization of dipoles and narrowing the broadening of trap density of states. Our work provides a promising strategy for enhancing the performance of OFETs by using interfacial flat-lying molecular monolayers.

A multi-layer of stacked-graphene (8 layers of basal planes) grown by chemical vapour deposition (CVD) is introduced as an artificial solid electrolyte interphase (SEI) layer onto a transition metal oxide cathode for lithium-ion batteries. The basal planes are generally regarded as a strong physical barrier that prevents lithium-ion diffusion, although it is believed that a small number of lithium-ions can migrate through the defect sites of the stacked layers. Interestingly, the unique design of the stacked-graphene perpendicular to the basal planes not only effectively suppresses the formation of instable SEI layers, but also achieves a reasonable amount of battery charge capacities. To correctly understand the impact from the stacked design, we further studied the rate kinetics difference between slow cycles (0.125 C→0.250 C→0.400 C→0.125 C) and rapid cycles (C→2 C→3 C→C). We propose that the clap-net like design of the stacked-graphene could enable the effective conducting pathway for electron transport, while protecting the active material inside. The magnetic measurements reveal the efficient Li+ (de)intercalation into graphene-layers. The artificial SEI also renders the electrode/electrolyte interface more stable against dynamic rate changes. The present approach provides a particular advantage in developing high stability battery that can be utilized at various charge rates.

When transferring photovoltaic technologies from laboratory-scale fabrication to industrial applications, low cost, large area, high throughput, high solar-to-energy power conversion efficiency, long lifetime, and low toxicity are crucial attributes. In recent years, organic–inorganic halide perovskite solar cells have emerged as a promising high-performance, cost-effective solar cell technology. However, most of the best reported efficiencies have been obtained on small active-area devices (∼0.1 cm 2 ). Therefore, development of protocols to industrialize such a technology is of paramount importance. In this article, we review the progress of perovskite solar cells with a particular emphasis on fabrication processes and instrumentation that have scale-up potential. For successful commercialization, the capacity to fabricate large-area modules is essential. Long-term stability is discussed, focusing on lifetime measurement and quantification protocols for commercialization. Cost-performance and life-cycle assessment analysis based on recently reported state-of-the-art perovskite solar cells are discussed. These analyses offer insights regarding required efficiency, module area size, and lifetime, in order for perovskite solar cells to be competitive with existing photovoltaic technologies. Finally, lead toxicity and possible solutions to this issue will be discussed. In the outlook, we outline future research directions based on reported results and trends in the field.

In organic field-effect transistors, the first few molecular layers at the semiconductor/dielectric interface are regarded as the active channel for charge transport; thus, great efforts have been devoted to the modification and optimization of molecular packing at such interfaces. Here, we report organic monolayers with large-area uniformity and high crystallinity deposited by an antisolvent-assisted spin-coating method acting as the templating layers between the dielectric and thermally evaporated semiconducting layers. The predeposited crystalline monolayers significantly enhance the film crystallinity of upper layers and the overall performance of transistors using these hybrid-deposited semiconducting films, showing a high carrier mobility up to 11.3 cm2 V–1 s–1. Additionally, patterned transistor arrays composed of the templating monolayers are fabricated, yielding an average mobility of 7.7 cm2 V–1 s–1. This work demonstrates a promising method for fabricating low-cost, high-performance, and large-...

To achieve industrially viable fabrication process for perovskite-based solar cells, every process step must be optimized for maximum throughput. We present a study of substituting laboratory-type UV-Ozone surface treatment with a high-throughput Corona treatment in a scalable perovskite solar cell fabrication process. It is observed that water contact angle measurements provide insufficient information to determine the necessary dose of Corona or UV-Ozone treatment, but the surface carbon signal measured by x-ray photoelectron spectroscopy accurately identifies when surface contamination has been completely removed. Furthermore, we observe highly accelerated de-contamination of ZnO surfaces by UV-Ozone treatment. The effect can be explained by photocatalytic O2− ion generation indicating that UV-Ozone treatment is also applicable in high-throughput processing.

An ever-growing demand for high-energy density and high-power Li-ion batteries has driven active research for electrode materials with superior capacity. Recent years have seen the development of Ni-rich transition metal oxide cathode materials due to their high reversible capacity and lower cost. To achieve full capacity from the charge compensation process, a high voltage (>4.4 V) charging is required. However, the battery operation at higher voltages eventually results in dramatic capacity fading and voltage decay with a rapid decomposition of the electrolyte upon further charge-discharge. While previous studies have reported the degradation mechanism within the electrode surface, there have been few empirical investigations into the solid-electrolyte interphase (SEI) formation on Ni-rich cathodes. In the current work, we visualize the different nature of the electrode-electrolyte interphase at various cut-off voltages (2.0-4.2 V, 2.0-4.5 V, and 2.0-4.8 V). We correlate the key properties of the SEI layer with the capacity fading mechanism in the high capacity battery system. The speciation of transition metal elements (Ni, Mn, and Co) into various oxidation and spin states has been identified as the dominant process of the capacity degradation.

Hybrid lead halide perovskites have emerged as promising active materials for photovoltaic cells. Although superb efficiencies have been achieved, it is widely recognized that long-term stability is a key challenge intimately determining the future development of perovskite-based photovoltaic technology. Herein, we present reversible and irreversible photodecomposition reactions of methylammonium lead iodide (MAPbI3). Simulated sunlight irradiation and temperature (40–80 °C) corresponding to solar cell working conditions lead to three degradation pathways: (1) CH3NH2 + HI (identified as the reversible path), (2) NH3 + CH3I (the irreversible or detrimental path), and (3) a reversible Pb(0) + I2(g) photodecomposition reaction. If only the reversible reactions (1) and (3) take place and reaction (2) can be avoided, encapsulated MAPbI3 can be regenerated during the off-illumination timeframe. Therefore, to further improve operational stability in hybrid perovskite solar cells, detailed understanding of how to mitigate photodegradation and thermal degradation processes is necessary. First, encapsulation of the device is necessary not only to avoid contact of the perovskite with ambient air, but also to prevent leakage of volatile products released from the perovskite. Second, careful selection of the organic cations in the compositional formula of the perovskite is necessary to avoid irreversible reactions. Third, selective contacts must be as chemically inert as possible toward the volatile released products. Finally, hybrid halide perovskite materials are speculated to undergo a dynamic formation and decomposition process; this can gradually decrease the crystalline grain size of the perovskite with time; therefore, efforts to deposit highly crystalline perovskites with large crystal sizes may fail to increase the long-term stability of photovoltaic devices.

Perovskite-based solar cell technology has advanced significantly and the power conversion efficiencies are nowadays on par with commercialized photovoltaic technologies. To realize the potential of perovskite solar cells, the focus is now shifting to scalable fabrication technologies that will enable low-cost solution processing of perovskite solar cells over large areas and with high yields. This review article discusses the fundamental concerns that arise when transitioning from laboratory to large area solution coating, available scalable coating technologies, and their applicability to the fabrication of high-performance perovskite solar cells. We find that a significant amount of work has been done to test scalable coating technologies, but also that often the methods that led to highest-performing cells in the laboratory (e.g. antisolvent processing) show limited compatibility with scalable coating methods. To achieve a high-yield and low-cost process, development must emphasize a high degree of control provided by sequential conversion of perovskite films and engineering of additives that fine-tune coating properties of perovskite precursor inks.

Since a hybrid perovskite‐based solar cell was reported for the first time, its efficiency and stability were boosted to remarkably high levels. With record efficiencies beyond 22 % and record stability up to 10 000 h under working conditions, perovskite solar cells are a promising candidate for further commercial applications. Among the myriads of fabrication methods to deposit perovskite films, we have chosen a unique technique that only needs methylamine gas (CH3NH2) to convert the inorganic film. In contrast to all other fabrication methods, this is based on room temperature and exposure to an organic gas exposure at ambient pressure, which can be easily employed for large‐area and fast coatings. In this Review, the advantages and characteristics of methylamine gas applications will be discussed. First, we will evaluate the different techniques to convert an inorganic film into a perovskite with an emphasis on the chemical interactions. Then, we will summarize the applications of methylamine gas to “heal” and improve the perovskite films prepared by other methods.

Organic–inorganic halide perovskite materials (e.g., MAPbI3, FAPbI3, etc.; where MA = CH3NH3+, FA = CH(NH2)2+) have been studied intensively for photovoltaic applications. Major concerns for the commercialization of perovskite photovoltaic technology to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still need for further exploration of alternative candidates. Elemental composition engineering of MAPbI3 and FAPbI3 has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Laboratory on perovskite-based solar cells, five are based on mixed perovskites (e.g., MAPbI1–xBrx, FA0.85MA0.15PbI2.55Br0.45, Cs0.1FA0.75MA0.15PbI2.49Br0.51). In this paper, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future research directions based on the reported results as well as related topics that warrant further investigation.(Some mathematical expressions are not properly displayed. Please see the attachment.)

Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of over 22%, and perovskite light-emitting diodes have recently achieved over 11% external quantum efficiency. To date, most research on perovskite light-emitting diodes has focused on solution-processed films. There are many advantages of a vapor-based growth process to prepare perovskites, including ease of patterning, ability to batch process, and material compatibility. We investigated an all-vapor perovskite growth process by chemical vapor deposition and demonstrated luminance up to 560 cd/m2.

The rapid rise of power conversion efficiency (PCE) of low cost organometal halide perovskite solar cells suggests that these cells are a promising alternative to conventional photovoltaic technology. However, anomalous hysteresis and unsatisfactory stability hinder the industrialization of perovskite solar cells. Interface engineering is of importance for the fabrication of highly stable and hysteresis free perovskite solar cells. Here we report that a surface modification of the widely used TiO2 compact layer can give insight into interface interaction in perovskite solar cells. A highest PCE of 18.5% is obtained using anatase TiO2, but the device is not stable and degrades rapidly. With an amorphous TiO2 compact layer, the devices show a prolonged lifetime but a lower PCE and more pronounced hysteresis. To achieve a high PCE and long lifetime simultaneously, an insulating polymer interface layer is deposited on top of TiO2. Three polymers, each with a different functional group (hydroxyl, amino, or aromatic group), are investigated to further understand the relation of interface structure and device PCE as well as stability. We show that it is necessary to consider not only the band alignment at the interface, but also interface chemical interactions between the thin interface layer and the perovskite film. The hydroxyl and amino groups interact with CH3NH3PbI3 leading to poor PCEs. In contrast, deposition of a thin layer of polymer consisting of an aromatic group to prevent the direct contact of TiO2 and CH3NH3PbI3 can significantly enhance the device stability, while the same time maintaining a high PCE. The fact that a polymer interface layer on top of TiO2 can enhance device stability, strongly suggests that the interface interaction between TiO2 and CH3NH3PbI3 plays a crucial role. Our work highlights the importance of interface structure and paves the way for further optimization of PCEs and stability of perovskite solar cells.

Ultrasonic spray coating is a promising pathway to scaling-up of perovskite solar cell production that can be implemented on any scale - from table-top to mass production. However, unlike spin-coating, spray coating processes are not easily described by a set of machine-independent parameters. In this work, in situ measurement and modeling of wet film thickness and evaporation rate are presented as a machine-independent description of the ultrasonic spray coating process, and applied to fabrication process optimization for high-performing perovskite solar cells. Optimization based on physical wet film parameters instead of machine settings leads to better understanding of the key factors affecting film quality and enables process transfer to another fabrication environment. Spray coated PbI2 film morphology is analyzed under a range of coating conditions and strong correlation is observed between spray coating parameters and PbI2 film uniformity. Premature precipitation and sparse nucleation are suggested as causes of film non-uniformity, and optimal process parameters are identified. Device fabrication based on the optimized process is demonstrated under ambient conditions with a relative humidity of 50%, achieving a power conversion efficiency of 13% in 1 cm2 area devices, with negligible hysteresis.

This themed issue includes a collection of articles on perovskite solar cells.

Increasing the stability of perovskites is essential for their integration in commercial photovoltaic devices. Halide mixing is suggested as a powerful strategy toward stable perovskite materials. However, the stabilizing effect of the halides critically depends on their distribution in the mixed compound, a topic that is currently under intense debate. Here we successfully determine the exact location of the I and Cl anions in the CH3NH3PbBr3–yIy and CH3NH3PbBr3–zClz mixed halide perovskite lattices and correlate it with the enhanced stability we find for the latter. By combining scanning tunneling microscopy and density functional theory, we predict that, for low ratios, iodine and chlorine incorporation have different effects on the electronic properties and stability of the CH3NH3PbBr3 perovskite material. In addition, we determine the optimal Cl incorporation ratio for stability increase without detrimental band gap modification, providing an important direction for the fabrication of stable perovskite devices. The increased material stability induced by chlorine incorporation is verified by performing photoelectron spectroscopy on a half-cell device architecture. Our findings provide an answer to the current debate on halide incorporation and demonstrate their direct influence on device stability., This work was supported by funding from the Energy Materials and Surface Sciences Unit of the Okinawa Institute of Science and Technology Graduate University, the OIST R&D Cluster Research Program, the OIST Proof of Concept (POC) Program, and JSPS KAKENHI Grant JP18K05266. The work at The University of Toledo was supported by the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science within the US Department of Energy. The theoretical calculation part used the resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC02-05CH11231. The work at ICN2 is funded by the CERCA Program/Generalitat de Catalunya, and supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706).

An ideal anti-counterfeiting label not only needs to be unclonable and accurate but also must consider cost and efficiency. But the traditional physical unclonable function (PUF) recognition technology must match all the images in a database one by one. The matching time increases with the number of samples. Here, a new kind of PUF anti-counterfeiting label is introduced with high modifiability, low reagent cost (2.1 × 10-4 USD), simple and fast authentication (overall time 12.17 s), high encoding capacity (2.1 × 10623 ), and its identification software. All inorganic perovskite nanocrystalline films with clonable micro-profile and unclonable micro-texture are prepared by laser engraving for lyophilic patterning, liquid strip sliding for high throughput droplet generation, and evaporative self-assembling for thin film deposition. A variety of crystal film profile shapes can be used as "specificator" for image recognition, and the verification time of recognition technology based on this divide-and-conquer strategy can be decreased by more than 20 times.

Defects as a result of structural imperfections and/or extrinsic impurities in the perovskite films have a detrimental effect on efficiency and stability of perovskite solar cells (PSCs). Here, we propose to use pre-synthesized crystalline perovskite with perfect stoichiometry to control and lower the density of defects from precursors by the powder engineering method. Compared with raw materials (i.e., PbI2 and FAI) based perovskites, the average efficiency of the PSCs fabricated based on these pre-synthesized perovskite precursors increased from 18.62% to 19.85%. Moreover, the unwanted intermediate chemical compositions (i.e., the unreacted phases and residual solvent) in the raw material-based perovskite films were significantly reduced in the pre-synthesized δ-FAPbI3 and α-FAPbI3 perovskites according to the secondary ion mass spectroscopy depth profiling results. Finally, we obtained the champion efficiency of 22.76% for α-FAPbI3 and 23.05% for FAPb(I0.9Br0.1)3 based PSCs. Long-term operational stability measurements of the encapsulated FAPb(I0.9Br0.1)3 based PSCs showed a slow decay and maintained the efficiency about 88% after 1200 h (T80 > 2000 h). Furthermore, a proof-of-concept integrated perovskite solar module-lithium ion battery-light-emitting diode device was demonstrated.

Efficient and stable parallel perovskite solar module is achieved by slot-die coating., Perovskite solar cells have emerged as one of the most promising thin-film photovoltaic (PV) technologies and have made a strong debut in the PV field. However, they still face difficulties with up-scaling to module-level devices and long-term stability issue. Here, we report the use of a room-temperature nonvolatile Lewis base additive, diphenyl sulfoxide(DPSO), in formamidinium-cesium (FACs) perovskite precursor solution to enhance the nucleation barrier and stabilize the wet precursor film for the scalable fabrication of uniform, large-area FACs perovskite films. With a parallel-interconnected module design, the resultant solar module realized a certified quasi-stabilized efficiency of 16.63% with an active area of 20.77 cm2. The encapsulated modules maintained 97 and 95% of their initial efficiencies after 10,000 and 1187 hours under day/night cycling and 1-sun equivalent white-light light-emitting diode array illumination with maximum power point tracking at 50°C, respectively.

The fabrication of CH3NH3PbI3 perovskite by solution processes is known to induce impurities in the film, which is usually correlated to the low photovoltage or fill factor of the solar cells. The nature of such defects is not always easy to identify and is described in general as grain boundaries containing dangling bonds, vacancies, interstitials, or impurities. In this work, perovskite films were fabricated with a very large and known concentration of impurities (PbI2, Pbx(O/OH)y) and further characterized using chronoamperometry and impedance spectroscopy. The IS data was carefully analyzed and compared with existing literature and a new interpretation is proposed according to the results. The IS features at high frequency and close to open circuit were attributed to the photogenerated charge recombination. Despite large impurity levels (>30 mol %), minor differences were observed in regard to charge recombination, which minimally affected the photovoltage.

The use of a solid hole transport layer (HTL) was transformational for the recent perovskite solar cell (PSC) revolution in solar energy technology. Often high efficiency PSC devices employ heavily doped hole transport materials such as spiro-MeOTAD. Independent of HTL chemistry, lithium-bis-trifluoromethanesulfonyl-imide (LiTFSI) and tert-butylpyridine (TBP) are commonly used as additives in HTL formulations for PSCs. LiTFSI and TBP were originally optimized for dye-sensitized solar cells, where their roles have been extensively studied. However, in the case of PSCs, the function of TBP is not clearly understood. In this study, properties of the HTL composite deposited on flat silicon substrates were systematically measured at several length scales, e.g., macroscopically (profilometry, 4-point probe conductivity, and thermogravimetry-differential thermal analysis), microscopically, and at the nanoscale to investigate film morphology, conductivity, and dopant distribution. Microscopic distributions of spi...

Perovskite-based solar cells, typically CH3NH3PbI3, have reached power conversion efficiencies on par with single crystal silicon solar cells. Perovskite cells prepared with the most common perovskite solvent N,N-dimethylformamide (DMF) by different research groups exhibit disparate efficiencies and stability for nominally identical perovskite films. Although the differences can be related to processing conditions, a consistent physical cause for the differences has been lacking. Highly-sensitive time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveals significant dimethylamine (DMA) included in perovskite films. TOF-SIMS and x-ray photoelectron spectroscopy results suggest DMA levels ranging from roughly 10–50%. Only the highest levels register as perovskite peak shifts in x-ray diffraction; lower levels are invisible. We propose that methylamine (MA) can react with DMF solvent by transamidation to produce dimethylamine (DMA), which then displaces some MA in perovskite crystals, see Fig. 1. Transamidation of DMF can be catalyzed by TiO2, Al2O3, water, or acid, but in perovskite films transamidation is inhibited by water.

In this work we performed dopant diffusion experiments on the hole transport material spiro-OMeTAD. Pure spiro-OMeTAD/F4-TCNQ doped spiro-OMeTAD and pure spiro-OMeTAD/DMC doped spiro-OMeTAD thin films were deposited on Au/Si(100) substrates. The energy levels, chemical states, and surface morphologies of formed films were studied by ultraviolet photoemission spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy as a function of the storage time in ultrahigh vacuum. We found only the pure spiro-OMeTAD/DMC doped spiro-OMeTAD film showed the n-type doping with the Fermi level of the film shifting away from the HOMO edge by 0.3 eV after 36 h. We propose that the diffusion of DMC dopant leads to the increase of the efficiencies of perovskite solar cell with the pin-hole free n-i-p structured hole transport layer several days after fabrication.

Solution processable perovskite solar cells traditionally use CH3NH3I solid powder as one of the two precursors that requires solvation into a solution and a spin-coating step; the resulting films need post-annealing (∼1 h) for complete conversion to CH3NH3PbI3. Here we describe for the first time the formation of stoichiometric perovskite in ambient air by exposing PbI2 films to a simple CH3NH2 gas precursor (as opposed to CH3NH3I solid powders). The reaction completes within a few seconds forming complete-coverage perovskite films with a roughness of 2 nm. The non-stoichiometric reaction produces Pb oxides as by-products, which are reconverted by further HI gas exposure. With combined measurements of the thin film crystal structure, chemical state, and absorption properties, we elucidate the chemical reaction mechanisms underlying these gas-induced processes. Fabricated solar cell devices show an efficiency of 15.3%, which remains almost the same after 133 days. Such a gas-induced reaction also enabled the successful preparation of high quality perovskite films with a size of 100 cm2.

Tailoring the interface energetics between a polymeric hole extraction layer (HEL) and a photoactive layer (PAL) in organic photovoltaics (OPVs) and organic–inorganic hybrid perovskite solar cells (PrSCs) is very important to maximize open circuit voltage (Voc), power conversion efficiency (PCE), and device lifetime. In principle, when Fermi-level pinning and a vacuum level shift take place between the HEL and PAL, they give rise to an energy level offset between the HEL and the valence band maximum (VBM) (or the highly occupied molecular orbital (HOMO) in the case of organic photoactive materials) of the PAL and then Voc loss. However, here we show that the Voc loss at the interface can be overcome by universal energy level tailoring of a self-organized HEL (SOHEL) between the HEL and PAL irrespective of photoactive materials. A SOHEL composed of a conducting polymer and a perfluorinated ionomer (PFI) is effectively used to study the interface energetics in OPVs and PrSCs. We systematically tailored the interface energy level of the SOHEL to remove the energy offset at the interface and understand clearly the universal energy level alignment with the diverse photoactive materials of OPVs and PrSCs. The Fermi-level of the HEL is pinned to the midgap state of photoactive materials, which is about 0.6–0.7 eV above the VBM or HOMO. However, the interface energy state of the PFI-enriched surface layer of the SOHEL can be formed deeper below the Fermi-level by self-organized molecules so that it can match the top of the valence band of the photoactive materials. As a result, the energy offset at the interface between photoactive materials and the SOHEL can be significantly decreased to achieve high Voc and PCE. Furthermore, our SOHEL significantly prolonged the stability of OPVs (half lifetime: 2.84 year) compared with pristine PEDOT:PSS (half lifetime: 0.2 year) under continuous irradiation of air mass-1.5 global simulated sunlight at 100 mW cm−2 due to the diffusion-blocking ability of the self-organized PFI at the surface of SOHELs for impurities from indium tin oxide.

We deposited lead-free CH3NH3SnBr3 – organometal halide perovskite films using two vapor deposition-based methods (i.e., co-evaporation and sequential evaporation) using SnBr2 and CH3NH3Br. We obtained comprehensive information about the structural and electronic properties of these Pb-free perovskite films. X-ray diffraction results confirmed the crystalline structure of MASnBr3. Using UV-Vis measurements, we determined the optical bandgap of these films to be ∼2.2 eV. On the basis of ultraviolet photoemission spectroscopy results, the work function and ionization energy were measured to be 4.3 and 6.1 eV, respectively. Solar cells employing such a perovskite film in a planar structure were fabricated with various hole transport layers (HTLs) (spiro-OMeTAD, C60, and P3HT). For perovskite films prepared by co-deposition, we obtained solar cell efficiencies ranging from 0.03 to 0.35%. On the other hand, when we used sequential deposition, a higher efficiency up to 1.12% was obtained using P3HT as the HTL. We confirmed that the low efficiency of MASnBr3 based perovskite solar cells is due to their relatively high resistance and the fast formation of Sn–Br oxide on the top surface by air exposure during fabrication. The sequential deposition method helped avoid such oxidation resulting in higher efficiencies.