A facile preparation of phase-stable cesium lead triiodide perovskite for high-performance solar cells.

Organometallic halide perovskite solar cells (PSCs) have shown great promise as a low-cost, high-efficiency photovoltaic technology. Structural and electro-optical properties of the perovskite absorber layer are most critical to device operation characteristics. Here we present a facile fabrication of high-efficiency PSCs based on compact, large-grain, pinhole-free CH3NH3PbI3−xBrx (MAPbI3−xBrx) thin films with high reproducibility. A simple methylammonium bromide (MABr) treatment via spin-coating with a proper MABr concentration converts MAPbI3 thin films with different initial film qualities (for example, grain size and pinholes) to high-quality MAPbI3−xBrx thin films following an Ostwald ripening process, which is strongly affected by MABr concentration and is ineffective when replacing MABr with methylammonium iodide. A higher MABr concentration enhances I–Br anion exchange reaction, yielding poorer device performance. This MABr-selective Ostwald ripening process improves cell efficiency but also enhances device stability and thus represents a simple, promising strategy for further improving PSC performance with higher reproducibility and reliability.

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...

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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.