Metal halide perovskite materials are emerging solution-processed semiconductors with considerable promise in optoelectronic devices 1,2 . Metal halide perovskite-based light-emitting devices (pLEDs) have received extensive interest for applications in flat-panel displays and solid-state lighting owing to their promise of low cost, tunable colors with narrow emission bandwidths, high photoluminescence quantum yield (PLQY), and facile solution processing [3][4][5][6][7] .However, the highest reported external quantum efficiency (EQE) of green-and red-emitting pLEDs are 14.36% 6,8 and 11.7% 7 , still far behind the performance of organic LEDs (OLEDs) [9][10][11] and inorganic quantum dot LEDs (QLEDs) 12 . Here we report visible perovskite LEDs that

The spontaneous α-to-δ phase transition of the formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by alloying with methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this Communication, we grow high-quality mixed cations and halides perovskite single crystals (FAPbI)(MAPbBr) to understand the principles for maintaining pure perovskite phase, which is essential to device optimization. We demonstrate that the best composition for a perfect α-phase perovskite without segregation is x = 0.1-0.15, and such a mixed perovskite exhibits carrier lifetime as long as 11.0 μs, which is over 20 times of that of FAPbI single crystal. Powder XRD, single crystal XRD and FT-IR results reveal that the incorporation of MA is critical for tuning the effective Goldschmidt tolerance factor toward the ideal value of 1 and lowering the Gibbs free energy via unit cell contraction and cation disorder. Moreover, we find that Br incorporation can effectively control the perovskite crystallization kinetics and reduce defect density to acquire high-quality single crystals with significant inhibition of δ-phase. These findings benefit the understanding of α-phase stabilization behavior, and have led to fabrication of perovskite solar cells with highest efficiency of 19.9% via solvent management.

Perovskite solar cells are strong competitors for silicon-based ones, but suffer from poor long-term stability, for which the intrinsic stability of perovskite materials is of primary concern. Herein, we prepared a series of well-defined cesium-containing mixed cation and mixed halide perovskite single-crystal alloys, which enabled systematic investigations on their structural stabilities against light, heat, water, and oxygen. Two potential phase separation processes are evidenced for the alloys as the cesium content increases to 10% and/or bromide to 15%. Eventually, a highly stable new composition, (FAPbI3)0.9(MAPbBr3)0.05­(CsPbBr3)0.05, emerges with a carrier lifetime of 16 μs. It remains stable during at least 10 000 h water–oxygen and 1000 h light stability tests, which is very promising for long-term stable devices with high efficiency. The mechanism for the enhanced stability is elucidated through detailed single-crystal structure analysis. Our work provides a single-crystal-based paradigm for stability investigation, leading to the discovery of stable new perovskite materials.

1603568(1 of 8) photoluminescence (PL) yield for potential optoelectronic application such as in LED and laser devices. [10][11][12][13][14][15][16][17][18] Luminescent MAPbBr 3 films have been deposited onto mesoporous Al 2 O 3 substrate. [19,20] Beside regular bulk lead halide perovskite, 2D or nanostructured lead halide perovskites had been previously synthesized for use as LEDs or other optoelectronic materials. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] These progresses have demonstrated the great success of classic solution chemistry method in the preparation of high quality lead halide nanocrystals with excellent photoluminescent properties for optoelectronic applications.It should be pointed out that although high quality nanocrystals can be successfully fabricated into devices via follow-up processes, a high quality film is more easy-to-process than nanocrystals suspensions for optoelectronic applications. For example, smooth lead halide perovskite films have been directly fabricated via simple one-step or two-step method in solar cell applications. [37] However, we found the high quality smooth planar MAPbBr 3 films for solar cells usually do not exhibit high photoluminescent properties as the nanocrystals suspension or the film deposited in the mesoporous Al 2 O 3 matrix. This is because the MAPbBr 3 films usually consist of large perovskite nanocrystals with size up to hundreds nanometers to micrometers, while the mesoporous support can be used to prevent crystal growth and control the particle size. As recently reported, lead halide perovskite nanoplate with quantum confine without the mesoporous support could grow in large crystals and thus lose the quantum confine effect. [38] It would be urgent to develop a facile method to fabricate highly luminescent perovskite-based film with good controllability and high stability.Metal-organic frameworks (MOFs) are periodic networks formed by coordination of metal ions with organic molecules. This configuration bears the similar structure as the organicinorganic perovskite from the viewpoints that both consist of the metal ions and organic molecules in the framework or lattice. Inspired by the ease preparation and various advantages of the MOFs configuration, [39][40][41] here, we report a strategy for fabricating highly luminescent and stable lead bromide The perovskite quantum dots are usually synthesized by solution chemistry and then fabricated into film for device application with some extra process. Here it is reported for the first time to in situ formation of a crosslinked 2D/3D NH 3 C 4 H 9 COO(CH 3 NH 3 ) n Pb n Br 3n perovskite planar films with controllable quantum confine via bifunctional amino acid crosslinkage, which is comparable to the solution chemistry synthesized CH 3 NH 3 PbBr 3 quantum dots. These atomic layer controllable perovskite films are facilely fabricated and tuned by addition of bi-functional 5-aminovaleric acid (Ava) of NH 2 C 4 H 9 COOH into regular (CH 3 NH 3 )PbBr 3 (MAPbBr 3 ) perovskite precursor solu...

Designing functional fullerenes with roles beyond defect passivation and electron‐transporting for perovskite solar cells (PSCs) is essential to the development of fullerenes and PSCs. Here, the authors design and synthesize a functional fullerene, FPD, composed of a C60 cage, a porphyrin ring, and three pentafluorophenyl groups. The structure features of FPD enable it can form chemical interactions with the perovskite lattices. These interactions enhance the defect passivation effect and prevent the decomposition of perovskite under irradiation. As a result, the FPD‐based device yields an improved power conversion efficiency of 23% with substantially enhanced operational stability (T80 > 1500 h). Furthermore, once got damaged, the FPD can prevent lead leakage by forming a stable and water‐insoluble complex (FPD‐Pb). Their findings provide a novel strategy to achieve high‐performance and eco‐friendly PSCs with functional fullerene materials.

Organolead halide perovskites exhibit superior photoelectric properties, which have given rise to the perovskite-based solar cells whose power conversion efficiency has rapidly reached above 20% in the past few years. However, perovskite-based solar cells have also encountered problems such as current-voltage hysteresis and degradation under practical working conditions. Yet investigations into the intrinsic chemical nature of the perovskite material and its role on the performance of the solar cells are relatively rare. In this work, Raman spectroscopy is employed together with CASTEP calculations to investigate the organic-inorganic interactions in CH3NH3PbI3 and CH3NH3PbBr3-xClx perovskite single crystals with comparison to those having ammonic acid as the cations. For Raman measurements of CH3NH3PbI3, a low energy line of 1030 nm is used to avoid excitation of strong photoluminescence of CH3NH3PbI3. Raman spectra covering a wide range of wavenumbers are obtained, and the restricted rotation modes of CH3-NH3(+) embedded in CH3NH3PbBr3 (325 cm(-1)) are overwhelmingly stronger over the other vibrational bands of the cations. However, the band intensity diminishes dramatically in CH3NH3PbBr3-xClx and most of the bands shift towards high frequency, indicating the interaction with the halides. The details of such an interaction are further revealed by inspecting the band shift of the restricted rotation mode as well as the C-N, NH3(+) and CH3 stretching of the CH3NH3(+) as a function of Cl composition and length of the cationic ammonic acids. The results show that the CH3NH3(+) interacts with the PbX3(-) octahedral framework via the NH3(+) end through N(+)-HX hydrogen bonding whose strength can be tuned by the composition of halides but is insensitive to the size of the organic cations. Moreover, an increase of the Cl content strengthens the hydrogen bonding and thus blueshifts the C-N stretching bands. This is due to the fact that Cl is more electronegative than Br and an increase of the Cl content decreases the lattice constant of the perovskite. The findings of the present work are valuable in understanding the role of cations and halides in the performance of MAPbX3-based perovskite solar cells.

Recently, low-bandgap formamidinium lead iodide FAPbI 3 -based perovskites are of particular interest for highperformance perovskite solar cells (PSCs) due to their broad spectral response and high photocurrent output. However, to inhibit the spontaneous α-to-δ phase transition, 15−17% (molar ratio) of bromide and cesium or methylammonium incorporated into the FAPbI 3 are indispensable to achieve efficient PSCs. In return, the high bromide content will increase bandgap and narrow the spectral response region. If simply reducing the bromide content, the corresponding PSCs exhibit inferior operational stability due to α-toδ phase transition, interface degradation, and halide migration. Herein, we report a CsPbBr 3 -cluster assisted vertically bottom-up crystallization approach to fabricate low-bromide (1% ∼ 6%), αphase pure, and MA-free FAPbI 3 -based PSCs. The clusters, in the size of several nanometers, could act as nuclei to facilitate vertical growth of high quality α-FAPbI 3 perovskite crystals. Moreover, these clusters can show further intake by perovskite after thermal annealing, which improves the phase homogeneity of the as-prepared perovskite films. As a result, the corresponding mesoporous PSCs deliver a champion efficiency of 21.78% with photoresponse extended to 830 nm. Moreover, these devices show remarkably improved operational stability, retaining ∼82% of the initial efficiency after 1,000 h of maximum power point tracking under 1 sun condition.

Understanding the function of moisture on perovskite is challenging since the random environmental moisture strongly disturbs the perovskite structure. Here, we develop various N2-protected characterization techniques to comprehensively study the effect of moisture on the efficient cesium, methylammonium, and formamidinium triple-cation perovskite (Cs0.05FA0.75MA0.20)Pb(I0.96Br0.04)3. In contrast to the secondary measurements, the established air-exposure-free techniques allow us directly monitor the influence of moisture during perovskite crystallization. We find a controllable moisture treatment for the intermediate perovskite can promote the mass transportation of organic salts, and help them enter the buried bottom of the films. This process accelerates the quasi-solid-solid reaction between organic salts and PbI2, enables a spatially homogeneous intermediate phase, and translates to high-quality perovskites with much-suppressed defects. Consequently, we obtain a champion device efficiency of approaching 24% with negligible hysteresis. The devices exhibit an average T80-lifetime of 852 h (maximum 1210 h) working at the maximum power point.