Search

Cathode–electrolyte interphase (CEI) formation between the cathode and the electrolyte is a critical factor that determines the stability of lithium-ion batteries (LiBs). The CEI layer consists of various by-products (e.g., LiF, Li2CO3, ROLi, and ROCO2Li (R: alkyl group)) decomposed from redox reactions between the cathode and the electrolyte, which can lead to dramatic capacity fading and stability issues. Herein, we empirically identify the energy level band bending of a Ni-rich NMC cathode (i.e., Li(Ni0.5Mn0.3Co0.2)O2) with the visual evidence of Li+ transfer from the electrode to the CEI layer (adsorbate). Negatively charged elements tend to be present at the close surface of the cathode, while the positively charged Li+ migrates from the cathode to the CEI layer. Hence, a downward band bending could be depicted based on the work function and the energy level difference between the Fermi level (EF) and the valence band maximum (EVBM). Energy level alignment itself is likely to be the key process that leads to the active formation of unstable CEI layers on charge–discharge.

Nickel oxide (NiOx) is a promising hole-selective contact to produce efficient inverted p-i-n structured perovskite solar cells (PSCs) due to its high carrier mobility and high transparency. However, the light-induced degradation of the NiOx–perovskite heterojunction is the main factor limiting its long-term operational lifetime. In this study, we used the time-resolved mass spectrometry technique to clarify the degradation mechanism of the NiOx-formamidinium–methylammonium iodide perovskite (a common composition for high-performance PSCs) heterojunction under operational conditions, and observed that (1) oxidation of iodide and generation of free protons under 1-sun illumination, (2) formation of volatile hydrogen cyanide, methyliodide, and ammonia at elevated temperatures, and (3) a condensation reaction between the organic components under a high vapor pressure. To eliminate these multi-step photochemical reactions, we constructed an aprotic trimethylsulfonium bromide (TMSBr) buffer layer at the NiOx/perovskite interface, which enables excellent photo-thermal stability, a matched lattice parameter with the perovskite crystal, and robust trap-passivation ability. Inverted PSCs stabilized with the TMSBr buffer layer reached the maximum efficiency of 22.1% and retained 82.8% of the initial value after continuous operation for 2000 hours under AM1.5G light illumination, which translates into a T80 lifetime of 2310 hours that is among the highest operational lifetimes for NiOx-based PSCs.

Upscalable fabrication of efficient and stable perovskite solar modules is urgently needed for commercialization. Here we introduce methylammonium chloride additives in the co-solvent system of N-methyl-2-pyrrolidone/N,N-dimethylformamide to control the formation of intermediate phases during the growth of formamidinium–caesium lead triiodide perovskite films. We achieve high-quality films upon drying without the use of anti-solvent. By implementing bulk and surface passivation, champion efficiencies of 24.02% for a small-sized solar cell and 20.5% for a 5 cm × 5 cm solar mini-module on an aperture area of 22.4 cm2 (geometric fill factor ∼ 96%) are achieved by spin-coating. The fully blade-coated perovskite solar sub-module demonstrates a champion efficiency of 15.3% on an aperture area of 205 cm2. The solar mini-module exhibits impressive operational stability with a T80 lifetime of over 1,000 h at maximum power point tracking under continuous light illumination.

Effective distribution coefficients of 9 impurities in 1,2-Diphenylethane have been calculated by directional crystallization under different ambient frozen temperature. The effect of varied zone size, temperature difference between the melt and ambient frozen environment, number of zone on purity of 1,2-Diphenylethane have been also investigated during the process of zone refining. The results indicate that the product purity in the intermediate purified region with varied zone size is higher 0.04%−0.2% than that with constant zone size. The product purity increases with temperature difference between the melt and ambient frozen environment. The appropriate temperature difference is adopted 50℃.The product purity in the intermediate region of sample bar with 2 molten zones is higher 0.05%−0.43% than that with 1 molten zone. In addition, the change of enthalpy and entropy between impurities and 1,2-Diphenylethane have been determined.

Lithium metal batteries are promising candidates for meeting the increasing demand for next-generation energy storage devices with high energy density; however, the problems of lithium dendrites and unstable solid electrolyte interphases (SEIs) for lithium anodes with nonaqueous electrolytes severely hinder their practical applications. The first step to address these issues is to establish a better understanding about these phenomena. In this review, we first discuss the formation processes and related mechanisms of dendritic lithium and SEIs, which are revealed and supported by the specially designed setups combined with various advanced characterization techniques including operando scanning transmission electron microscopy (STEM) and deduced theoretical models. Because of the high sensitivity of lithium metal anodes to the ambient environment, their microscopic characterization remained challenging until the development of noninvasive cryogenic electron microscopy. Then, we present the real-state atomic structures and chemical compositions of lithium dendrites and SEIs by cryogenic transmission electron microscopy (cryo-TEM) coupled with electron energy loss spectroscopy (EELS). Based on these fundamental insights, various strategies including electrolyte engineering, construction of artificial SEI layers, and use of three-dimensional hosts for lithium, introduced to solve the lithium anode problems, are summarized. Finally, the future directions and opportunities regarding lithium anode research are discussed.

Flexible perovskite solar cells (F-PSCs) hold promise for portable power sources for applications in various fields, such as wearable and portable electronics and lightweight power supply in stratosphere and space applications. To date, it is still a challenge to achieve efficient and stable F-PSCs. Herein, a pre-applied strain on a flexible substrate to release the residual strain of the perovskite layers of the F-PSCs is reported. As a result, the F-PSC based on this strategy yielded a power conversion efficiency (PCE) of up to 18.71%, approaching that of its counterpart based on a glass substrate (20.32%). And it retained 90% of its initial PCE after 300 h under AM 1.5G light illumination with an extrapolated T80 lifetime (the time over which the device efficiency reduces to 80% of its initial value) exceeding 700 h. Furthermore, the PCE remained above 80% of its initial value even after 1500 tension-only bending cycles. The result of this work paves a possible way toward fabricating efficient and stable F-PSCs.

Herein, we report the use of pyridine anchoring group functionalized poly(triarylamine) (p-PY) as a hole transport layer at buried interfaces between the ITO and formamidinium–cesium perovskite layer to enhance the efficiency and stability of inverted PSCs.

Perovskite solar cells (PSCs) are a promising third-generation photovoltaic (PV) technology developed rapidly in recent years. Further improvement of their power conversion efficiency is focusing on reducing the non-radiative charge recombination induced by the defects in metal halide perovskites. So far, defect passivation by the organic small molecule has been considered as a promising approach for boosting the PSC performance owing to their large structure flexibility adapting to passivating variable kinds of defect states and perovskite compositions. Here, the recent progress of defect passivation toward efficient and stable PSCs was reviewed from the viewpoint of molecular structure design and device performance. To comprehensively reveal the structure-performance correlation of passivation molecules, it was separately discussed how the functional groups, organic frameworks, and side chains affect the corresponding PV parameters of PSCs. Finally, a guideline was provided for researchers to select more suitable passivation agents, and a perspective was given on future trends in development of passivation strategies.

CsPbCl3 nanocrystals are potential ultrapure emitters. But it is challenging to synthesize CsPbCl3 nanocrystals with sufficient stability, which impedes their application in light-emitting devices. In this work, we report a facile phosphoryl-chemistry-mediated synthesis approach to synthesizing stable CsPbCl3 nanocrystals, in which the phenylphosphonic dichloride (PhPOCl2) precursor is employed. In addition to the high reactivity of the P–Cl bond of PhPOCl2 for providing adequate Cl, the derived P=O with good proton affinity facilitates the formation of a distinct nanocrystal surface with the nonprotonated oleylamine (OLA) ligand. Accordingly, the L-type-ligand-capped CsPbCl3 nanocrystals exhibited not only bright luminance but also good stability that endured repeated purification up to 10 cycles. Based on the stable CsPbCl3 nanocrystals, we achieved violet LEDs with extremely narrow electroluminescence spectra (full width at half-maximum ≈ 10.6 nm).

Metal halide perovskites (MHPs) have become a major topic of research in thin film photovoltaics due to their advantageous optoelectronic properties. These devices typically have the MHP absorber layer sandwiched between two charge selective layers (CSLs). The interfaces between the perovskite layer and these CSLs are potential areas of higher charge recombination. Understanding the nature of these interfaces is key for device improvement. Additionally, non-stoichiometric perovskite films are expected to strongly impact the interfacial properties. In this study, the interface between CH3NH3PbI3 (MAPbI3) and copper phthalocyanine (CuPc), a hole transport layer (HTL), is studied at the atomic scale. We use scanning tunneling microscopy (STM) combined with density functional theory (DFT) predictions to show that CuPc deposited on MAPbX3 (X = I,Br) forms a self-assembled layer consistent with the α-polymorph of CuPc. Additionally, STM images show a distinctly different adsorption orientation for CuPc on non-perovskite domains of the thin film samples. These findings highlight the effect of non-stoichiometric films on the relative orientation at the MHP/HTL interface, which may affect interfacial charge transport in a device. Our work provides an atomic scale view of the MHP/CuPc interface and underscores the importance of understanding interfacial structures and the effect that the film stoichiometry can have on interfacial properties.

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.

Suppressing nucleation over large areas Although formamidinium-based lead iodide (PbI 2 ) perovskites have a favorable bandgap and good thermal stability, the difficulty in controlling nucleation makes it difficult to grow high-quality, large-area films compared with methylammonium counterparts. Bu et al. show that adding N -methyl-2-pyrrolidone to the perovskite precursors forms an adduct with PbI 2 that promotes the formation of the desired black α-phase at room temperature. The addition of potassium hexafluorophosphate eliminated hysteresis by passivating interfacial defects and promoted long-term thermal stability at 85°C in unencapsulated devices. Large-area modules (17 square centimeters) achieved power conversion efficiencies of 20.4%. Science , abh1035, this issue p. 1327

We present an efficient and easy synthesis method for incorporating organocatalytic moieties into Zr-metal organic frameworks (Zr-MOFs). The catalytic activity and selectivity of the new chiral catalysts were improved by adjusting the aperture of the MOF cavities. The hole size of the Zr-MOF was modulated by adding acid and replacing bridge ligands during synthesis. The difunctional chiral units of amino acid-thiourea are anchored onto the Zr-MOF by a mild synthesis method from an isothiocyanate intermediate which could effectively avoid the racemization of chiral moieties in the synthesis process. By means of specific surface area measurement (BET), scanning electron microscopy (SEM) and powder X-ray Diffraction (PXRD), it was confirmed that Zr-MOFs with different pore sizes were synthesized without breaking the basic octahedral structure of the MOF. Finally, good yields (up to 83%) and ee values (up to 73%) were achieved with the new heterogeneous catalysts in 48 hours for the aldol reaction of 4-nitrobenzaldehyde with acetone. By contrast, using the catalyst support without modulating the synthesis, the yield (30%) and the ee-value (26%) were both low. Experiments have confirmed the important influence on the reaction selectivity of providing a suitable reaction environment by controlling the aperture of MOF cavities.

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.

Flexible solar cells, which are compatible with low cost and high throughput roll-to-roll manufacturing, are specifically attractive for applications in wearable/portable electronic devices, building-integrated photovoltaics (BIPV), drones and satellites, etc. Integration of the narrow bandgap flexible solar cells, e.g., Cu(In, Ga)(S, Se)2 solar cells, organic solar cells, or the new class of lead-tin mixed perovskite solar cells (PSCs) with wide bandgap NIR-transparent PSCs allows two sub-cells to utilize solar light with different photon energies more efficiently and therefore minimizes thermalization loss to overcome the theoretical Shockley–Queisser single-junction limit (33%). In this review, we provide an overview of the recent progress of flexible perovskite-based tandem solar cells from the perspective of the narrow bandgap bottom cell and the near-infrared (NIR) transparent top cell. In addition, we discuss the key limitations related to energy losses in the recombination layer in two-terminal (2-T) tandems and the optical losses in four-terminal (4-T) tandems. Then we outline several strategies to overcome these limitations. Finally, we provide an outlook on roll-to-roll manufacturing and device encapsulation.

Metal halide perovskite solar cells are an emerging photovoltaic technology already exhibiting great potential. The main challenges at present that hinder the application of perovskite solar cells include scalable fabrication, operational stability, and environmental impact of Pb in Pb-containing perovskite solar cells. Among various scalable coating techniques, modified chemical vapor deposition (CVD) is a promising technology to enable large-area and uniform coating of perovskite layers at a low cost. Modified CVD also offers many other advantages such as being solvent-free, high compatibility with industrial manufacturing, and easy integration with other solar technologies to form tandem cells (or perovskite–perovskite tandem cells). In this review, we present the recent development of perovskite solar cells and modules prepared by modified CVD. We first discuss the differences between modified CVD and solution coating processing. We then summarize the present results from the cost-performance analysis point of view to show the potential of modified CVD for scalable fabrication of perovskite solar cells and modules with low cost. At the end of this review, we outline several future research directions.