No abstract

This communication reports that the TiO2@polydopamine nanocomposite with a core-shell structure could be a highly active photocatalyst working under visible light. A very thin layer of polydopamine at around 1 nm was found to be critical for the degradation of Rhodamine B.

Mixed organolead halide perovskites (MOHPs), CH 3 NH 3 Pb(Br x I 1Àx ) 3 ,h ave been shown to undergo phase segregation into iodide-richd omains under illumination, which presents am ajor challenge to their development for photovoltaic and light-emitting devices.Recent work suggested that phase-segregated domains are localized at crystal boundaries,driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, am ethod for growing large (30 30 1 mm 3 )m onocrystalline MAPb(Br x I 1Àx ) 3 single crystals is presented. The direct visualization of the growth of nanocluster-like I-richd omains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time-resolved spectroscopyp rovided new insight into the nature of the phase-segregated domains and the collective impact on the optoelectronic properties.

To date, the most efficient perovskite solar cells (PSCs) employ an n–i–p device architecture that uses a 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) hole‐transporting material (HTM), which achieves optimum conductivity with the addition of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. However, this additive along with its oxidation process leads to poor reproducibility and is detrimental to stability. Herein, a dicationic salt spiro‐OMeTAD(TFSI)2, is employed as an effective p‐dopant to achieve power conversion efficiencies of 19.3% and 18.3% (apertures of 0.16 and 1.00 cm2) with excellent reproducibility in the absence of LiTFSI and air exposure. As far as it is known, these are the highest‐performing n–i–p PSCs without LiTFSI or air exposure. Comprehensive analysis demonstrates that precise control of the proportion of [spiro‐OMeTAD]+ directly provides high conductivity in HTM films with low series resistance, fast hole extraction, and lower interfacial charge recombination. Moreover, the spiro‐OMeTAD(TFSI)2‐doped devices show improved stability, benefitting from well‐retained HTM morphology without forming aggregates or voids when tested under an ambient atmosphere. A facile approach is presented to fabricate highly efficient PSCs by replacing LiTFSI with spiro‐OMeTAD(TFSI)2. Furthermore, this study provides an insight into the relationship between device performance and the HTM doping level.

Forming uniform metal oxide nanocoatings is a well-known challenge in the construction of core-shell type nanomaterials. Herein, by using buffer solution as a specific reaction medium, we demonstrate the possibility to grow thin nanoshells of metal oxides, typically Al2 O3 , on different kinds of core materials, forming a uniform surface-coating layer with thicknesses achieving one nanometer precision. The application of this methodology for the surface modification of LiCoO2 shows that a thin nanoshell of Al2 O3 can be readily tuned on the surface for an optimized battery performance.

Photoinduced phase segregation in mixed halide perovskites has received considerable attention due to its critical roles in diminishing device performance in photovoltaic and light‐emitting applications. Here, dynamic photoinduced phase segregation and dark recovery in mixed halide perovskite single crystal microplatelets are investigated, combining depth‐resolved, temporal‐resolved, and detection‐wavelength selective spectroscopic imaging techniques. Under identical illumination, the edges and interior of microplatelets exhibit significantly different phase segregation. An intimate correlation of PL dynamics between I‐phase and Br‐phase indicates that the halide substitution is the dominant effect. In the dark, the phase‐segregated crystals reversibly recover to the stable equivalence. This work clarifies the critical role of the edge state of the microplatelets and reveals the physical mechanism of phase segregation in mixed halide perovskites, which is of crucial importance for their applications in photovoltaics and photonics.

Organo-lead halide perovskites (OHPs) have recently emerged as a new class of exceptional optoelectronic materials, which may find use in many applications, including solar cells, light emitting diodes, and photodetectors. More complex applications, such as lasers and electro-optic modulators, require the use of monocrystalline perovskite materials to reach their ultimate performance levels. Conventional methods for forming single crystals of OHPs like methylammonium lead bromide (MAPbBr ) afford limited control over the product morphology, rendering the assembly of defined microcavity nanostructures difficult. We overcame this by synthesizing for the first time (MA)[PbBr ]⋅DMF (1), and demonstrating its facile transformation into monocrystalline MAPbBr microplatelets. The MAPbBr microplatelets were tailored into waveguide based photonic devices, of which an ultra-low propagation loss of 0.04 dB μm for a propagation distance of 100 μm was demonstrated. An efficient active electro-optical modulator (AEOM) consisting of a MAPbBr non-linear arc waveguide was demonstrated, exhibiting a 98.4 % PL intensity modulation with an external voltage of 45 V. This novel synthetic approach, as well as the demonstration of effective waveguiding, will pave the way for developing a wide range of photonic devices based on organo-lead halide perovskites.

Novel surface modification of self-assembling large cations enables the achievement of high quality perovskite films for hysteresis-free and stable solar cells with an optimized efficiency over 20%.