Controllable Black-to-Yellow Phase Transition by Tuning the Lattice Symmetry in Perovskite Quantum Dots.

The black-to-yellow phase transition in perovskite quantum dots (QDs) is more complex than in bulk perovskites, regarding the role of surface energy. Here, with the assistance of in situ grazing-incidence wide-angle and small-angle X-ray scattering (GIWAXS/GISAXS), distinct phase behaviors of cesium lead iodide (CsPbI ) QD films under two different temperature profiles-instant heating-up (IHU) and slow heating-up (SHU) is investigated. The IHU process can cause the phase transition from black phase to yellow phase, while under the SHU process, the majority remains in black phase.

Over-18%-Efficiency Quasi-2D Ruddlesden-Popper Pb-Sn Mixed Perovskite Solar Cells by Compositional Engineering.

Quasi-two-dimensional (2D) Pb-Sn mixed perovskites show great potential in applications of single and tandem photovoltaic devices, but they suffer from low efficiencies due to the existence of horizontal 2D phases. Here, we obtain a record high efficiency of 18.06% based on 2D ⟨⟩ = 5 Pb-S mixed perovskites (-BAMA(PbSn)I, = 0.

High-Efficiency Low-Lead Perovskite Photovoltaics Approaching 20% Enabled by a Vacuum-Drying Strategy.

Lead-tin mixed perovskites are excellent photovoltaic materials that can be used in single- or multi-junction perovskite solar cells (PSCs). However, most high-performance Pb-Sn mixed PSCs reported to date are still Pb-dominant. It is highly demanding to develop environmentally friendly low-lead PSCs, but the poor film quality caused by the uncontrollable crystallization kinetics has been hindering the efficiency improvement of low-lead PSCs.

Critical Influence of Organic A'-Site Ligand Structure on 2D Perovskite Crystallization.

Organic A'-site ligand structure plays a crucial role in the crystal growth of 2D perovskites, but the underlying mechanism has not been adequately understood. This problem is tackled by studying the influence of two isomeric A'-site ligands, linear-shaped n-butylammonium (n-BA ) and branched iso-butylammonium (iso-BA ), on 2D perovskites from precursor to device, with a combination of in situ grazing-incidence wide-angle X-ray scattering and density functional theory. It is found that branched iso-BA , due to the lower aggregation enthalpies, tends to form large-size clusters in the precursor solution, which can act as pre-nucleation sites to expedite the crystallization of vertically oriented 2D perovskites.

High Open Circuit Voltage Over 1 V Achieved in Tin-Based Perovskite Solar Cells with a 2D/3D Vertical Heterojunction.

2D-3D mixed tin halide perovskites are outstanding candidate materials for lead-free perovskite solar cells (PSCs) due to their improved stability and decreased trap density in comparison with their pure 3D counterparts. However, the mixture of multiple phases may lead to poor charge transfer across the films and limit the device efficiency. Here, a stacked quasi-2D (down)-3D (top) double-layered structure in perovskite films prepared via vacuum treatment is demonstrated, which can result in a planar bilayer heterojunction.

Highly oriented MAPbI crystals for efficient hole-conductor-free printable mesoscopic perovskite solar cells.

Highly crystalline perovskite films with large grains and few grain boundaries are conducive for efficient and stable perovskite solar cells. Current methods for preparing perovskite films are mostly based on a fast crystallization process, with rapid nucleation and insufficient growth. In this study, MAPbI perovskite with inhibited nucleation and promoted growth in the TiO/ZrO/carbon triple mesoscopic scaffold was crystallized by modulating the precursor and the crystallization process.

Excess Ion-Induced Efficiency Roll-Off in High-Efficiency Perovskite Light-Emitting Diodes.

Applying extensively excess ammonium halides in forming perovskites is a widely used approach to achieve high-performance perovskite light-emitting diodes (PeLEDs). However, most of these PeLEDs suffer from severe external quantum efficiency (EQE) roll-off at high current densities, thereby restricting the realization of high-brightness PeLEDs and laser diodes. In this work, we explore the underlying mechanism of the EQE roll-off in high-efficiency formamidinium lead iodide (FAPbI)-based PeLEDs.

High-Performance Blue Perovskite Light-Emitting Diodes Enabled by Efficient Energy Transfer between Coupled Quasi-2D Perovskite Layers.

While there has been extensive investigation into modulating quasi-2D perovskite compositions in light-emitting diodes (LEDs) for promoting their electroluminescence, very few reports have studied approaches involving enhancement of the energy transfer between quasi-2D perovskite layers of the film, which plays very important role for achieving high-performance perovskite LEDs (PeLEDs). In this work, a bifunctional ligand of 4-(2-aminoethyl)benzoic acid (ABA) cation is strategically introduced into the perovskite to diminish the weak van der Waals gap between individual perovskite layers for promoting coupled quasi-2D perovskite layers. In particular, the strengthened interaction between coupled quasi-2D perovskite layers favors an efficient energy transfer in the perovskite films.

Efficient Slantwise Aligned Dion-Jacobson Phase Perovskite Solar Cells Based on Trans-1,4-Cyclohexanediamine.

The crystalline orientation and phase distribution are two important parameters for high-performance 2D perovskite solar cells. Therefore, it is essential to understand how the structure of spacer ligands influences the orientation and phase distribution of resulting 2D perovskite films. In this work, a new member of Dion-Jacobson (DJ) phase 2D perovskites based on trans-1,4-cyclohexanediamine (CHDA) is demonstrated and it is found that the crystalline orientation is self-aligned spontaneously, which is different from the well-known graded distribution in controlled sample with its isomer 1,6-diaminohexane (HDA) as spacer ligand.

Precise Control of Perovskite Crystallization Kinetics via Sequential A-Site Doping.

Two-step-fabricated FAPbI -based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI -based perovskite film with sequential A-site doping of Cs and GA is revealed by in situ X-ray scattering and first-principles calculations.

Hierarchical cobalt-based hydroxide microspheres for water oxidation.

3D hierarchical cobalt hydroxide carbonate hydrate (Co(CO3)0.5(OH)·0.11H2O) has been synthesized featuring a hollow urchin-like structure by a one-step hydrothermal method at modest temperature on FTO glass substrates.

Hierarchical wreath-like Au-Co(OH)2 microclusters for water oxidation at neutral pH.

Hierarchical Au-Co(OH)2 microclusters have been synthesized by a facile ethanol-assisted hydrothermal method on FTO glass substrates. The as-fabricated Au-Co(OH)2 forms a typical wreath-shaped structure on a nanosheet with an urchin-like Au-Co(OH)2 structure located in the centre surrounded by densely grown Co(OH)2 nanoarrays. Morphological evolution of the Au-Co(OH)2 microclusters through intermediate steps could be identified by varying the reaction time.