Construction and Interfacial Modification of a ß-PbSnF4 Electrolyte with High Intrinsic Ionic Conductivity for a Room-Temperature Fluoride-Ion Battery.

Solid-state fluoride-ion batteries (FIBs) attract significant attention worldwide because of their high theoretical volume, energy density, and high safety. However, the large interfacial resistance caused by the point-point contact between the electrolyte and the electrode seriously impedes their further development. Using liquid-phase therapy to construct a conformal interface is a good choice to eliminate the influence of inadequate contact between the electrode and the electrolyte. In this study, a ß-PbSnF4 solid-state electrolyte with high room-temperature ionic conductivity is prepared, and a trace amount of the liquid electrolyte (LE) between the electrode and the electrolyte is introduced in order to minimize the interfacial resistance and enhance the cycle life. The Allen-Hickling simulations show that the introduction of an interfacial wetting agent (LE) can significantly reduce the energy barrier of charge transfer and mass transfer processes at the interface and reciprocate FIBs an enhanced interfacial reaction kinetics. As a result, the initial discharge capacity of the fabricated FIBs is 210.5 mAh g-1 and the capacity retention rate is 82.6% after 50 cycles at room temperature, while the initial discharge capacity of the unmodified battery is only 170.9 mAh g-1 and the capacity retention rate is 22.1% after 50 cycles. Therefore, interfacial modification with a trace amount of LE provides a significant exploration for the improvement of FIB performances.

Improved Structural Order and Exciton Delocalization in High-Member Quasi-Two-Dimensional Tin Halide Perovskite Revealed by Electroabsorption Spectroscopy.

Engineering of quasi-two-dimensional (quasi-2D) tin halide perovskite structures is a promising pathway to achieve high-performance lead-free perovskite solar cells, with recently developed devices demonstrating over 14% efficiency. Despite the significant efficiency improvement over the bulk three-dimensional (3D) tin perovskite solar cells, the precise relationship between structural engineering and electron-hole (exciton) properties is not fully understood. Here, we study exciton properties in high-member quasi-2D tin perovskite (which is dominated by large n phases) and bulk 3D tin perovskite using electroabsorption (EA) spectroscopy. By numerically extracting the changes in polarizability and dipole moment between the excited and ground states, we show that more ordered and delocalized excitons are formed in the high-member quasi-2D film. This result indicates that the high-member quasi-2D tin perovskite film consists of more ordered crystal orientations and reduced defect density, which is in agreement with the over 5-fold increase in exciton lifetime and much improved solar cell efficiency in devices. Our results provide insights on the structure-property relationship of high-performance quasi-2D tin perovskite optoelectronic devices.

In-situ growth of low-dimensional perovskite-based insular nanocrystals for highly efficient light emitting diodes.

Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices. However, judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology, composition, and defect. Herein, we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization. The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX3 perovskite, respectively. The formation of supramolecular structure retard perovskite nucleation, while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth. This judicious control enables a segmented growth, inducing the growth of insular nanocrystal consist of low-dimensional structure. Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%, ranking among the highest efficiency achieved. The homogeneous nano-island structure also enables high-efficiency large area (1 cm2) device up to 21.6%, and a record high value of 13.6% for highly semi-transparent ones.

Surface-Energy-Regulated Growth of α-Phase Cs0.03 FA0.97 PbI3 for Highly Efficient and Stable Inverted Perovskite Solar Cells.

Methylammonium (MA)-free formamidinium (FA)-dominated Csx FA1-x PbI3 is rising as the most promising candidate for highly efficient and stable perovskite solar cells. However, the growth of high-quality Csx FA1-x PbI3 black-phase perovskite structure without ion doping in the lattice remains a challenge. Herein, propeller-shaped halogenated tertiary ammonium is synthesized, showing high binding energy on the perovskite surface and large steric hindrance. This molecule can significantly reduce the barrier of high surface energy that suppresses the growth of the α-phase Csx FA1-x PbI3 structure. As a result, the α-phase structure can be formed at room temperature, which can further act as a seed for the growth of high-quality film. Solar cells based on the film show a record efficiency up to 23.6% for MA free Csx FA1- x PbI3 solar cells with inverted structure and excellent stability at 85 °C over 200 h.

Efficient Mutual-Compensating Li-Loss Strategy toward Highly Conductive Garnet Ceramics for Li-Metal Solid-State Batteries.

Garnet-type Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte (SSE) due to its high Li+ conductivity and stability against lithium metal. However, wide research and application of LLZO are hampered by the difficulty in sintering highly conductive LLZO ceramics, which is mainly attributed to its poor sinterability and the hardship of controlling the Li2O atmosphere at a high sintering temperature (∼1200 °C). Herein, an efficient mutual-compensating Li-loss (MCLL) method is proposed to effectively control the Li2O atmosphere during the sintering process for highly conductive LLZO ceramics. The Li6.5La3Zr1.5Ta0.5O12 (LLZTO) ceramic SSEs sintered by the MCLL method own high relative density (96%), high Li content (5.54%), high conductivity (7.19 × 10-4 S cm-1), and large critical current density (0.85 mA cm-2), equating those sintered by a hot-pressing technique. The assembled Li-Li symmetric battery and a Li-metal solid-state battery (LMSSB) show that the as-prepared LLZTO can achieve a small interfacial resistance (17 Ω cm2) with Li metal, exhibits high electrochemical stability against Li metal, and has broad potential in the application of LMSSBs. In addition, this method can also improve the sintering efficiency, avoid the use of mother powder, and reduce raw-material cost, and thus it may promote the large-scale preparation and wide application of LLZO ceramic SSE.

One-Step Synthesis of SnI2·(DMSO)x Adducts for High-Performance Tin Perovskite Solar Cells.

Contemporary thin-film photovoltaic (PV) materials contain elements that are scarce (CIGS) or regulated (CdTe and lead-based perovskites), a fact that may limit the widespread impact of these emerging PV technologies. Tin halide perovskites utilize materials less stringently regulated than the lead (Pb) employed in mainstream perovskite solar cells; however, even today's best tin-halide perovskite thin films suffer from limited carrier diffusion length and poor film morphology. We devised a synthetic route to enable in situ reaction between metallic Sn and I2 in dimethyl sulfoxide (DMSO), a reaction that generates a highly coordinated SnI2·(DMSO)x adduct that is well-dispersed in the precursor solution. The adduct directs out-of-plane crystal orientation and achieves a more homogeneous structure in polycrystalline perovskite thin films. This approach improves the electron diffusion length of tin-halide perovskite to 290 ± 20 nm compared to 210 ± 20 nm in reference films. We fabricate tin-halide perovskite solar cells with a power conversion efficiency of 14.6% as certified in an independent lab. This represents a ∼20% increase compared to the previous best-performing certified tin-halide perovskite solar cells. The cells outperform prior earth-abundant and heavy-metal-free inorganic-active-layer-based thin-film solar cells such as those based on amorphous silicon, Cu2ZnSn(S/Se)4 , and Sb2(S/Se)3.

Low-Dimensional Inorganic Tin Perovskite Solar Cells Prepared by Templated Growth.

The manipulation of the dimensionality and nanostructures based on the precise control of the crystal growth kinetics boosts the flourishing development of perovskite optoelectronic materials and devices. Herein, a low-dimensional inorganic tin halide perovskite, CsSnBrI2-x (SCN)x , with a mixed 2D and 3D structure is fabricated. A kinetic study indicates that Sn(SCN)2 and phenylethylamine hydroiodate can form a 2D perovskite structure that acts as a template for the growth of the 3D perovskite CsSnBrI2-x (SCN)x . The film shows an out-of-plane orientation and a large grain size, giving rise to reduced defect density, superior thermostability, and oxidation resistance. A solar cell based on this low-dimensional film reaches a power conversion efficiency of 5.01 %, which is the highest value for CsSnBrx I3-x perovskite solar cells. Furthermore, the device shows enhanced stability in ambient air.

Suppressing the Voltage Decay Based on a Distinct Stacking Sequence of Oxygen Atoms for Li-Rich Cathode Materials.

Li-rich cathode materials possess a much higher theoretical energy density than all intercalated cathode materials currently reported and thus are considered as the most promising candidate for next-generation high-energy density Li-ion batteries. However, the rapid voltage decay and the irreversible phase transition of O3-type Li-rich cathode materials often lessen their actual energy density and limit their practical applications, and thus, effectively suppressing the voltage decay of Li-rich cathodes becomes the hotspot of the current research. Herein, the F-doped O2-type Li-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2+δ-xFx (F-O2-LRO) are designed and prepared based on the P2-type sodium-ion cathode materials Na5/6Li1/4(Mn0.54Ni0.13Co0.13)3/4O2+δ (Na-LRO) by ion exchange. It has been found that the as-prepared F-O2-LRO exhibits excellent electrochemical performance, for example, a high discharge specific capacity of 280 mA h g-1 at 0.1 C with an initial Coulombic efficiency of 94.4%, which is obviously higher than the original LRO (77.2%). After 100 cycles, the F-O2-LRO cathode can still maintain a high capacity retention of 95% at a rate of 1 C, while the capacity retention of the original LRO is only 69.1% at the same current rate. Furthermore, the voltage difference (ΔV) of F-O2-LRO before and after cycling is only 0.268 V after 100 cycles at 1 C, which is less than that of the LRO cathode (0.681 V), indicating much lower polarization. Besides, even at a high current rate of 5 C, F-O2-LRO still displays a satisfactory discharge capacity of 210 mA h g-1 with a capacity retention of 90.1% after 100 cycles. Therefore, this work put forward a new strategy for the development and industrial application of Li-rich cathode materials in high-energy Li-ion batteries.