All-inorganic perovskite cesium lead halide quantum dots (QDs) have been widely investigated as promising materials for optoelectronic application because of their outstanding photoluminescence (PL) properties and benefits from quantum effects. Although QDs with fullspectra visible emission have been synthesized for years, the PL quantum yield (PLQY) of pure blue-emitting QDs still stays at a low level, in contrast to their green-or redemitting counterparts. Herein, we obtained core−shell structured cubic CsPbBr 3 @amorphous CsPbBr x (A-CsPbBr x ) perovskite QDs via a facile hot injection method and centrifugation process. The core−shell structure QDs showed a record blue emission PLQY of 84%, which is much higher than that of blue-emitting cubic CsPbBr 3 QDs and CsPbBr x Cl 3−x QDs. Furthermore, a blue-emitting QDsassisted LED with bright pure blue emission was prepared and illustrated the core−shell QDs' promising prospect in optoelectrical application.

Strain engineering has emerged as a powerful tool to create new states of known materials with excellent performance. Here, we show a general and practically realizable method via interphase strain to obtain a new super tetragonality providing giant polarization. This method is illustrated for the case of PbTiO3, where we report a c/a ratio of up to 1.238 in epitaxial composite thin films, compared to that of 1.065 in bulk PbTiO3. These thin films of super-tetragonal structure possess an unprecedented giant remanent polarization, 236.3 μC/cm 2 , which is almost twice the value of all known ferroelectrics. The tetragonal phase is stable up to 725 °C as compared to the bulk's transition temperature of 490 °C. The present interphase strain approach could provide a new avenue to enhance the physical properties of materials with respect to their multiferroic, photonic, superconductor, and energy-harvesting behavior.

A fully automated spray-coated technology with ultrathin-film purification is exploited for the commercial large-scale solution-based processing of colloidal inorganic perovskite CsPbI 3 quantum dot (QD) films toward solar cells. This process is in the air outside the glove box. To further improve the performance of QD solar cells, the short-chain ligand of phenyltrimethylammonium bromide (PTABr) with a benzene group is introduced to partially substitute for the original long-chain ligands of the colloidal QD surface (namely PTABr-CsPbI 3 ). This process not only enhances the carrier charge mobility within the QD film due to shortening length between adjacent QDs, but also passivates the halide vacancy defects of QD by Br − from PTABr. The colloidal QD solar cells show a power conversion efficiency (PCE) of 11.2% with an open voltage of 1.11 V, a short current density of 14.4 mA cm −2 , and a fill factor of 0.70. Due to the hydrophobic surface chemistry of the PTABr-CsPbI 3 film, the solar cell can maintain 80% of the initial PCE in ambient conditions for one month without any encapsulation. Such a low-cost and efficient spraycoating technology also offers an avenue to the film fabrication of colloidal nanocrystals for electronic devices.with a large bandgap of 2.82 eV. [24,25] Many efforts have tried to partly replace I − with Br − to increase the stability of the black phase. [17,26,27] Unfortunately, the introduction of the bromine component enlarges the bandgap of the perovskite, correspondingly to harm the light-harvesting performance. The cubic structure of CsPbI 3 also can be stabilized by the colloidal quantum dot (QD) method, because the enlarging surface energy inhibits the phase transition. [28][29][30] In addition, on the basis of the multiple exciton generation effects, the narrow bandgap colloidal QDs will exceed the single-junction Shockley-Queisser solar efficiency limit to achieve higher theoretical efficiency. [31,32] Several efforts have built the devices with quite inspiring efficiency using the CsPbI 3 QD film as the active layer. [14,30,[33][34][35][36][37][38] However, the CsPbI 3 QDs are usually deposited to form the thin film by the spin-coating method. This method is an undesirable way to realize the scaled manufacture of the QD thin film because of the small deposition area. [39] To economize the cost of materials and realize scalable film deposition, the spray coating is emerging as a typical process for the fabrication of the thin films and has been used in the commercial paint coat technology. [32,39] However, the spray-coating process is hard to obtain high quality compact thin-film of colloidal QD due to long chain surface organic ligands of QD that weakens the adhesive force between QD and substrate. The surface ligands are obstructive to the formation of QD films and performance of the devices by hindering the charge transport. But the surface ligands are necessary to maintain monodisperse QDs and suppress their agglomeration. How to balance the surface ligands and the adhesive f...

No abstract

Cesium halide perovskite CsPbX3 has emerged to be a promising candidate for photovoltaic materials due to their componential and thermal stability. During the fabrication of CsPbX3 films, rich halide ions could cause deep trap states on the surface of the perovskite film, leading to much charge recombination. Herein, Pb2+ solution post‐processing strategy is introduced to passivate the deep trap states of CsPbI2Br films. The dissociative Pb2+ in the solution effectively combines with the excess halide ions on the perovskite surface to reduce the deep trap states of Pb vacancy (VPb) and I interstitial (Ii). As a result, the average photoluminescence lifetimes τave of the perovskite film prolonged nearly double after passivation. The trap density of perovskite is effectively decreased from 8 × 1016 to 6.64 × 1016 cm−3. The CsPb2Br solar cell shows an open‐circuit‐voltage as high as 1.29 V and power conversion efficiency of 12.34% with small hysteresis. The postprocessing method would provide an avenue to improve further the efficiency of inorganic perovskite solar cells via reducing surface traps.

Inorganic halide perovskites exhibit significant photovoltaic performance due to their structural stability and high open-circuit voltage ( V). Herein, a general strategy of solution engineering has been implemented to enable a wide solution-processing window for high V (∼1.3 V) and power conversion efficiency (PCE, ∼12.5%). We introduce a nontoxic solvent of dimethyl sulfoxide (DMSO) and an assisted heating process in the fabrication of CsPbIBr (CPI2) to control the improved crystallization. A wide solution-processing window including a wide range of solvent components and solute concentrations has been realized. The CPI2-based inorganic perovskite solar cells (IPSCs) exhibit a high PCE up to 12.52%. More importantly, these devices demonstrate a remarkable V of 1.315 V. The performance has possessed such a region with high V and PCE in all Cs-based IPSCs, unveiling wide solution-processing windows with enhanced solution processability facilitating potential industrial application especially for tandem solar cells.

Organic-inorganic halide perovskites have recently attracted strong research interest for fabrication of high-performance, lowcost photovoltaic devices. Recently, we reported a highly reproducible procedure to fabricate high-performance organic-inorganic halide perovskite solar cells. This procedure, based on a onestep, solvent-induced, fast deposition-crystallization method, involves the use of sec-butyl alcohol as a new solvent to induce the CH 3 NH 3 PbI 3 fast crystallization deposition. In the present study, we propose a reproducible fabrication method to prepare both flat and large-grain perovskite film by adding a pre-annealing step to strengthen the perovskite nucleation, aiming to facilitate the excess CH 3 NH 3 I and solvent removal in the sec-butyl alcohol soaking process, in which all films with thickness between 420 nm and 1 mm performed uniformly. The best performing planar device obtained with this procedure had an efficiency of 17.2% under AM 1.5G illumination and an average power conversion efficiency of 16.2 AE 0.5%. We also analyzed the efficiency of halide perovskite planar solar cells as a function of the perovskite film thickness; the efficiency dropped only slightly to 15.7% when the perovskite film thickness was increased to 1 mm.

In article number 1906615, Jianjun Tian and co‐workers describe a fully automated spray‐coating technology with ultrathin‐film purification for a commercial large‐scale solution‐based process for colloidal inorganic perovskite CsPbI3 quantum dot (QD) films. The QD solar cells based on such films show a high power conversion efficiency of 11.2% and can maintain 80% of initial efficiency in air ambient for one month without any encapsulation.