The fabrication of multidimensional organometallic halide perovskite via a low‐pressure vapor‐assisted solution process is demonstrated for the first time. Phenyl ethyl‐ammonium iodide (PEAI)‐doped ...lead iodide (PbI2) is first spin‐coated onto the substrate and subsequently reacts with methyl‐ammonium iodide (MAI) vapor in a low‐pressure heating oven. The doping ratio of PEAI in MAI‐vapor‐treated perovskite has significant impact on the crystalline structure, surface morphology, grain size, UV–vis absorption and photoluminescence spectra, and the resultant device performance. Multiple photoluminescence spectra are observed in the perovskite film starting with high PEAI/PbI2 ratio, which suggests the coexistence of low‐dimensional perovskite (PEA2MAn−1PbnI3n+1) with various values of n after vapor reaction. The dimensionality of the as‐fabricated perovskite film reveals an evolution from 2D, hybrid 2D/3D to 3D structure when the doping level of PEAI/PbI2 ratio varies from 2 to 0. Scanning electron microscopy images and Kelvin probe force microscopy mapping show that the PEAI‐containing perovskite grain is presumably formed around the MAPbI3 perovskite grain to benefit MAPbI3 grain growth. The device employing perovskite with PEAI/PbI2 = 0.05 achieves a champion power conversion efficiency of 19.10% with an open‐circuit voltage of 1.08 V, a current density of 21.91 mA cm−2, and a remarkable fill factor of 80.36%.
A high‐efficiency perovskite solar cell using 2D/3D hybrid perovskite prepared by a low‐pressure vapor‐assisted solution process is demonstrated. Phenyl ethyl‐ammonium iodide (PEAI)‐containing 2D perovskite forms around the MAPbI3 perovskite grain and is beneficial for MAPbI3 grain growth. The optimized device employing perovskite with PEAI/PbI2 = 0.05 achieves a promising power conversion efficiency of 19.10% with an open‐circuit voltage of 1.08 V.
This review presents various hole transport layers (HTLs) employed in perovskite solar cells (PSCs) in pursuing high power conversion efficiency (PCE) and functional stability. The PSCs have achieved ...high PCE (over 23%, certified by NREL) and more efforts have been devoted into research for stability enhancement. Inorganic HTLs become a popular choice as selective contact materials because of their intrinsic chemical stability and low cost. HTLs and electron transport layers (ETLs) are critical components of PSCs due to the requirement to create charge collection selectivity. Herein the authors provide an overview on inorganic HTLs synthesis, properties, and their application in various PSCs for both mesoporous and planar architectures. Inorganic HTLs with appropriate properties, such as proper energy level and high carrier mobility, can not only assist with charge transport, but also improve the stability of PSCs under ambient conditions. The importance of interfacial chemistry and interfacial charge transport is further addressed to understand the underlying mechanism of related degradation and carrier dynamic. It is expected that the success of the inorganic HTL in PSCs can stimulate further research and bring real impact for future photovoltaic technologies.
The perovskite solar cell (PSC) has boosted its power conversion efficiency along with the application of inorganic hole transport layer (HTL). The presence of inorganic HTL assist the carrier transport and improve the stability. Wide variety of inorganic HTLs are reviewed in this report along with their properties, synthesis technique and interfacial chemistry and carrier dynamic.
Perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) over 25%. Though their high PCE can be achieved by optimizing absorber layer and device interfaces, the ...intrinsic instability of perovskite materials is still a key issue to be resolved. Mixed‐halide perovskites using multiple halogen constituents have been proved to improve robustness; however, the anion at the X site in the ABX3 formula is not limited to halogens. Other negative monovalent ions with similar properties to halogens, such as pseudo‐halogens, have the opportunity to form perovskites with ABX3 stoichiometry. Recently, thiocyanates and formates have been utilized to synthesize stable perovskite materials. This review presents the evolution of pseudo‐halide perovskite solar cells in the past few years. The intrinsic properties, their effects on crystal structure, and bandgap engineering of the pseudo‐halide perovskites are summarized. Various thiocyanate compounds applied in the fabrication of perovskite solar cells are discussed. The fabrication process, film formation mechanism, and crystallinity of pseudo‐halide perovskites are elucidated to understand their effects on the photovoltaic performance and device stability. Other applications of pseudo‐halide perovskites are summarized in the final section. Lastly, this review concludes with suggestions and outlooks for further research directions.
Monovalent pseudo‐halide anions share similar properties to halide anions. This review presents the evolution of pseudo‐halide perovskite solar cells in the past few years. The role of pseudo‐halides and their position and occupation in perovskite crystal, its impact on perovskite film quality, solar cell stability and photovoltaic performance, and pseudo‐halide optoelectronic devices beyond solar cells are compared comprehensively.
This study examines the spatial distributions of precipitation during active and quiet times. Most previous studies commonly classified precipitation into different energy spectral types, but we ...utilized a classification according to particle energy channels. A general conclusion derived from these distributions suggests that regardless of active and quiet times, low‐energy (<1 keV) and high‐energy precipitating particles are mostly on the dayside and nightside, respectively. A comparison with past results reveals that the high‐energy electron precipitation during quiet times is mostly due to wave scattering and that during active times is mainly produced by quasi‐static potential structures (QSPS) and Alfvénic acceleration, while low‐energy electron precipitation is mostly caused by QSPS and Alfvénic acceleration regardless of quiet and active times. For both high‐energy proton and electron precipitation, the nightside dawn‐dusk asymmetry of their distributions during active times is found to be opposite of that during quiet times. We infer that the distribution of high‐energy precipitation during quiet times is dominated by the curvature and gradient drifts, while during active times it is mainly due to the physical processes or phenomena related to substorms in the magnetotail. Empirical orthogonal function analysis has been applied in this study to derive where the flux has the maximum enhancement as the geomagnetic activity increases. The results further demonstrate that low‐energy and high‐energy protons mainly increase in the noon and postmidnight sectors, respectively. The highest enhancements of low‐energy and high‐energy electrons are in the prenoon and premidnight sectors, respectively.
Plain Language Summary
The dynamic nature of the magnetosphere can precipitate charged particles into the upper atmosphere in the high‐latitude region, creating spectacular auroras. The number and energy fluxes of these particles and their distributions vary with the geomagnetic activity. When people studied particle precipitation, they usually categorized the precipitation according to the monoenergetic, broadband, and diffuse features shown in energy spectra. Using new categorization criteria based on different energy channels, we can conclude that, in general, low‐energy channels (154–224 and 688–1,000 eV) are mostly distributed on the dayside, while high‐energy channels (2,115–3,075 and 6,503–9,457 eV) are mainly distributed on the nightside regardless of geomagnetic conditions and particle charge types. Our results also demonstrate an intriguing dawn‐dusk asymmetric distribution of high‐energy protons/electrons on the nightside in reference to the magnetospheric state. High‐energy precipitating protons and electrons are respectively on premidnight and postmidnight during quiet times because of the regular drift motion of the magnetospheric particles, but their distributions during active times are swapped due to the physical processes of substorms in the magnetotail. All the results derived from this study provide a new look at particle precipitation, which can help reveal the secret of the dynamic magnetosphere.
Key Points
A new method of categorizing particle precipitation using energy channels is implemented
Low‐energy (high‐energy) precipitation is, in general, mostly on the dayside (nightside) regardless of geomagnetic states
The dawn‐dusk asymmetric distribution of high‐energy protons/electrons during quiet times is the opposite of that during active times
Dayside cusp aurorae are created from particles precipitating into the cusp, and ionospheric convection is driven by solar wind electric fields. In this study, we coordinated the observations ...obtained from the all‐sky camera on Svalbard, the Super Dual Auroral Radar Network, SuperMAG magnetometer data, and far ultraviolet imagers on board the Defense Meteorological Satellite Program satellites for the event January 4, 2014 to examine the morphology of aurorae and the patterns of ionospheric convection for radial interplanetary magnetic field (IMF). During the event, a poleward‐moving auroral form and antisunward ionospheric convection were observed when the IMF turned into almost purely radial. Moreover, both types of antisunward and sunward convection were simultaneously observed near the footprint of the cusp at different times during the radial IMF period. The antisunward convection and sunward convection are typically an indicator of the dayside reconnection for the southward IMF and the lobe reconnection for the northward IMF, respectively. All those observations support the concept of low‐latitude dayside and high‐latitude lobe reconnection for the radial IMF. This study further shows that the coexistence of the two types of reconnection for radial IMF, resulting in an interplay of repetitive antisunward and sunward convection.
Plain Language Summary
The event for January 4, 2014 enables us to study the features of dayside cusp aurorae and ionospheric convection for the radial IMF. During the event, a poleward‐moving auroral form and antisunward convection were observed near the footprint of the cusp, which provides indirect evidence of the magnetic reconnection that occurs at the dayside magnetopause for the radial IMF. S‐shaped aurorae, named from their morphology, near the cusp were also observed during the event. This type of aurora was possibly created by magnetosheath plasma jets impinging on the surface of the magnetopause or magnetic reconnection occurring locally on the magnetopause. For ionospheric convection, the primary convection pattern for the radial IMF was similar to that for the southward IMF, particularly for antisunward convection near the cusp. However, sunward convection near the cusp was also observed at the same time, indicating the lobe reconnection coexists with the dayside reconnection. In summary, the features of dayside cusp aurorae and ionospheric convection for the northward and southward IMFs can be seen at different times during the radial IMF event.
Key Points
A period of almost purely radial interplanetary magnetic field (IMF) (cone angle < 3°) was embedded in the radial IMF event for January 4, 2014
IMF By or Bz related poleward‐moving aurora was created by precipitating electrons along the open field lines in the cusp during the period
The antisunward ionospheric convection became stable and consistent with magnetometer observations when the IMF was almost purely radial
Cu/Cu2O films grown by ion beam sputtering were used as p-type modified layers to improve the efficiency and stability of perovskite solar cells (PSCs) with an n-i-p heterojunction structure. The ...ratio of Cu to Cu2O in the films can be tuned by the oxygen flow ratio (O2/(O2 + Ar)) during the sputtering of copper. Auger electron spectroscopy was performed to determine the elemental composition and chemical state of Cu in the films. Ultraviolet photoelectron spectroscopy and photoluminescence spectroscopy revealed that the valence band maximum of the p-type Cu/Cu2O matches well with the perovskite. The Cu/Cu2O film not only acts as a p-type modified layer but also plays the role of an electron blocking buffer layer. By introducing the p-type Cu/Cu2O films between the low-mobility hole transport material, spiro-OMeTAD, and the Ag electrode in the PSCs, the device durability and power conversion efficiency (PCE) were effectively improved as compared to the reference devices without the Cu/Cu2O interlayer. The enhanced PCE is mainly attributed to the high hole mobility of the p-type Cu/Cu2O film. Additionally, the Cu/Cu2O film serves as a protective layer against the penetration of humidity and Ag into the perovskite active layer.
The soft and polar nature of quasi‐2D (PEA)2PbBr4 perovskite, and robust photo‐generated excitons lead exciton‐polaritons and exciton‐polarons as the important phenomena near the band edge for ...application in the lighting aspect. In this work, a convenient methodology is proposed based on the polariton resonant modes in temperature‐dependent (77 K to RT) spectroscopy, and investigate the effect of these quasi‐particles on refractive index dispersion. The large binding energy (≈335 meV) of quasi‐2D excitons is obtained by the reflectance measurements at 77 K. Stable exciton‐polaritons and exciton‐polarons are confirmed by energy dispersions and the observation of self‐trapped exciton‐polaron state, respectively. Furthermore, the large negative thermal‐optic coefficient due to damping effect of exciton‐phonon scattering is observed. The phenomenon is opposite to those observed in conventional semiconductors (e.g., Si, Ge, GaN, AlN, GaAs, AlAs, and ZnO etc.). The observed stable negative thermal‐optic coefficients from 160 K to RT indicate that the quasi‐2D perovskite can be used as a phase compensator for conventional semiconductor materials.
The shrinkage of the energy difference between lower polariton branches (LPs) and upper polariton branches (UPs) proves that oscillator strength decreases when the temperature rises from 77 to 300 K. Therefore, the strong damping effect of exciton‐phonon interactions reduces the oscillator strength when the temperature rises, and further result in the negative thermal‐optic behaviors of quasi‐2D (PEA)2PbBr4 perovskite.
Considering the increasing global demand for energy and the harmful ecological impact of conventional energy sources, it is obvious that development of clean and renewable energy is a necessity. ...Since the Sun is our only external energy source, harnessing its energy, which is clean, non-hazardous and infinite, satisfies the main objectives of all alternative energy strategies. With attractive features, i.e., good performance, low-cost potential, simple processibility, a wide range of applications from portable power generation to power-windows, photoelectrochemical solar cells like dye-sensitized solar cells (DSCs) represent one of the promising methods for future large-scale power production directly from sunlight. While the sensitization of n-type semiconductors (n-SC) has been intensively studied, the use of p-type semiconductor (p-SC), e.g., the sensitization of wide bandgap p-SC and hole transport materials with p-SC have also been attracting great attention. Recently, it has been proved that the p-type inorganic semiconductor as a charge selective material or a charge transport material in organometallic lead halide perovskite solar cells (PSCs) shows a significant impact on solar cell performance. Therefore the study of p-type semiconductors is important to rationally design efficient DSCs and PSCs. In this review, recent published works on p-type DSCs and PSCs incorporated with an inorganic p-type semiconductor and our perspectives on this topic are discussed.
In this report, we fabricated thiocyanate‐based perovskite solar cells with low‐pressure vapor‐assisted solution process (LP‐VASP) method. Photovoltaic performances are evaluated with detailed ...materials characterizations. Scanning electron microscopy images show that SCN‐based perovskite films fabricated using LP‐VASP have long‐range uniform morphology and large grain sizes up to 1 μm. The XRD and Raman spectra were employed to observe the characteristic peaks for both SCN‐based and pure CH3NH3PbI3 perovskite. We observed that the Pb(SCN)2 film transformed to PbI2 before the formation of perovskite film. X‐ray photoemission spectra (XPS) show that only a small amount of S remained in the film. Using LP‐VASP method, we fabricated SCN‐based perovskite solar cells and achieved a power conversion efficiency of 12.72 %. It is worth noting that the price of Pb(SCN)2 is only 4 % of PbI2. These results demonstrate that pseudo‐halide perovskites are promising materials for fabricating low‐cost perovskite solar cells.
Pseudohalide, solid performance: Pseudohalide SCN‐based perovskite layers are fabricated using the low‐pressure vapor‐assisted solution processing method. The formation mechanism, full characterization of the films, and the SCN/I ratio in the final perovskite films are investigated. Devices fabricated using these films yielded power conversion efficiency values of 12.72 % with nearly 90 % of the initial PCE maintained after a 10 day stability test.
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