Nanoheterostructures (NHSs) based on lead halide perovskites (LHPs) and chalcogenide quantum dots have proved to be promising candidates for photovoltaic device applications. However, understanding the defect chemistry at the interfaces of LHPs and chalcogenides is essential to stabilize them and further tune their optoelectronic properties. Here, we demonstrate a route for designing CsPbBr3-PbSe NHSs and other derivatives of LHP-based NHSs using defect-rich MoSe2 nanosheets (NSs) and study the effect of the size of PbSe NPs on their optical properties. In this synthesis route, PbSe nanoparticles (NPs) are formed at an early stage of the reaction through a unique cation displacement reaction, over which CsPbBr3 nanocrystals (NCs) are epitaxially grown. Using this methodology, a nearly 3-fold enhancement in photoluminescence (PL) is achieved, whereas other selenium precursors, which form larger PbSe NPs, result in negligible PL enhancement with respect to the pure CsPbBr3 NCs. Detailed density functional theory (DFT) calculations suggest that the PbSe NPs are responsible for passivating the surface defects that consequently enhance the PL intensity. However, in the case of larger PbSe NPs, the associated valence and conduction bands lie within the band-gap region of CsPbBr3, creating a type-I heterostructure between the two materials, thereby affecting the luminescence properties. Strong passivation of surface defects in CsPbBr3-PbSe NHSs is also evidenced from low-temperature PL studies. Furthermore, the resulting CsPbBr3-PbSe NHSs demonstrate enhanced stability in the presence of water and do not degrade under ambient conditions for several months.

Cu 3 TaS 4 , a ternary chalcogenide, is a promising photovoltaic material. The growth of Cu 3 TaS 4 occurs via the formation of Cu 2− x S with Cu vacancies. Ta incorporation occurs in the Cu 2− x S at Cu vacancy sites, followed by diffusion of Ta to form Cu 3 TaS 4 .

We show that the colloidal growth of SnS nanosheets (NS), a group IV metal chalcogenide (MC), on MoSe2 NS, a transition metal dichalcogenide (TMDC), results in the formation of type-II nanoheterostructures (NHS). The MoSe2/SnS NHS synthesis is accompanied by in situ generation of MoO3-x at the MoSe2 and SnS interface activating the otherwise electrochemically inert basal planes of MoSe2 NS. The MoSe2/SnS NHS exhibit more active sites, and the built-in electric field at the interface enhances the rate of charge transfer. The largely enhanced electrocatalytic activities are attributed to the electronic property manipulation due to the synergistic interactions between MoSe2 NS and SnS NS. This work provides insights into the design of multicomponent low-dimensional 2D/2D (D = dimension) NHS based on TMDC/MC combination with enhanced electrochemical properties, in particular for applications of water splitting.

Two-dimensional (2D) layered Ruddlesden-Popper metal halide perovskites (MHPs) show enhanced stability compared to threedimensional (3D) MHPs. The general formula of 2D layered perovskite is L(2)A(n-1)M(n)X(3n+1), where L is the large organic spacer and n is the number of metal octahedra. However, the syntheses of such 2D layered perovskites yield a mixture of 3D and 2D layered perovskites with different layers of the metal octahedra. In this work, we have synthesized 2D layered (MA)(n+1)PbnI3n+1 perovskite by the sonochemical method. We have shown that the dimensionality n can be controlled by the sonication time and reaction temperature. Using absorption and photoluminescence spectroscopy, we have probed the reaction and growth mechanisms of the 2D layered perovskites and their transformation to 3D MAPbI(3) (MAPI). At both lower temperature and early stage of the reaction, 2D layered perovskites with lower dimensionality form and eventually covert to higher-dimensional layered perovskite before transforming to 3D perovskites. The dissimilarity in the solubility of the precursors (PbI2 and MAI) is responsible for such transformations. We show that these mixed (2D layered and 3D MAPI) perovskites can be used to fabricate a white light-emitting diode.

Anion exchange of CsPbX3 nanocrystals (NCs) is an easy pathway to tune the bandgap over the entire visible region. Even the mixing of pre-synthesized CsPbBr3 and CsPbI3 NCs at room temperature leads to the formation of mixed halide CsPbBr3-xIx NCs. Understanding the reaction mechanism and the kinetics of interparticle mixing is essential for fundamental aspects and device applications. Here, we probed the kinetics of ion migration through time-dependent steady-state photoluminescence (PL) spectroscopy. We found three primary PL peaks after the mixing of NCs-bromide side peak, iodide side peak, and a new peak that emerges during the reaction. The reaction follows first-order kinetics and the activation energy is 0.75 ± 0.05 eV. We propose that the free oleylammonium halides which are in dynamic equilibrium with the NCs, eventually promote interparticle mixing that follows the anion migration from the surface to the core of the nanocrystal, which is the rate-limiting step. Overall, the inherent reaction rate between the halide anions and the nanocrystals governs the reaction kinetics.

Lead-free halide perovskites have attracted interest in the photovoltaic industry out of concern for the toxic nature of the lead. Antimony-based perovskite, cesium antimony iodide (Cs3Sb2I9), is o...

The health hazards associated with heavy metal ions in water demand the development of efficient and portable sensors, for rapid onsite detection of these ions. Several research groups have developed colorimetric/visual sensors based on plasmonic nanomaterials and quantum dots (QDs). Attempts for specific detection of metal ions have been partially achieved through the interaction between the metal ion and the passivating ligands around the QD. However, the underlying mechanism is not clearly understood. Here, we have used water-soluble Mn-doped ZnS QD to effectively detect Hg2+, Pb2+, and Cd2+ through the quenching of QD emission and understand the mechanism of sensing. Stern-Volmer plots indicate that the quenching is static in nature for Pb2+, and Cd2+, while for Hg2+, it is a combination of static and dynamic quenching. Overall, the metal ions bind to the QD through the passivating ligand. After excitation, the electron from the conduction band of the QD can get injected to the metal ion - which decreases the photoluminescence of the QD. The electron injection depends on the reduction potential of the metal ion, the orbital overlap and the overall stabilization energy of the metal ions bound to the QD. Hence, this method of sensing is not selective to a specific metal ion. A solid state sensor of QD-rGO composite detects Pb2+ down to 0.4 ppb. The findings will be important for future improvement of colorimetric/visual sensors based on QD emission.

A new 2-methoxy-4,6-bis(4-(4-nitrostyryl)phenyl)nicotinonitrile (W-NO2) has been synthesized and the photovoltaic performances in dye-sensitized solar cells (DSSCs) are investigated by utilizing it as co-sensitizer dye. From the study, its molar extinction coefficient value is found to be much higher than the N719 and the co-sensitized DSSC device showed a 1.78 times better efficiency than the N719 based devices. Preliminary DSSC results also revealed that the molecular architecture of dye (W-NO2) can be effectively utilized as a co-sensitizer along with the N719 to increase the spectral coverage as well as to achieve improved efficiency.

New cyanopyridine derivatives bearing different alkoxy substituents were designed and synthesized to study their optical and electrochemical properties. All the synthesized compounds were characterized using various spectroscopic techniques like IR, NMR, and Mass spectrometry. Their optical and electrochemical properties were explored with the aid of UV-visible spectroscopy, photoluminescence spectroscopy and cyclic voltammetry. Further, these compounds exhibited a very good solubility in organic solvents such as toluene, chloroform, ethyl acetate, THE and DMSO. Therefore, these compounds showed absorption band in the region of 274-355 nm and a blue emission band in the region of 412-438 nm. Finally, their cyclic voltammetry measurements revealed that the energy band gap of the molecules are lies between 1.37 eV and 2.12 eV. As a whole, the obtained preliminary results suggest that these compounds can be used further as optoelectronic materials.

A new class of molecular architecture made of five conjugated rings carrying terminal methyl or variable alkoxy (chain lengths of 4, 6, 8, or 16) substituted at para positions has been synthesized. Among the five rings, two rings are of cyanopyridones utilized as an electron deficient N-heterocycle along with blue luminescent motif, and the rest of them are phenylene motifs. All the compounds produced good yield and ATR-IR, NMR and Mass spectroscopy confirmed their structures. Further, the compounds were stable up to approximate to 200 degrees C and the degradation occurs at higher temperature as evident from the TGA analysis. The mesomorphic study reveals that compound is only having very long terminal n-hexadecyloxy substituents appeared in-layers liquid crystalline organization as confirmed by POM and variable temperature XRD analysis. Further, the compounds showed intense blue fluorescence in both solution as well as solid state and their fluorescence quantum yields are dependent on the length of alkoxy chains. Calculated HOMO/WMO levels by cyclic voltammetry measurements revealed that the compounds are ambipolar in nature and cited as an ideal candidates for electroluminescent applications. (C) 2018 Elsevier B.V. All rights reserved.

Three new fluorescent bent shaped conjugated compounds have been designed and synthesized by linking two 3,4-dialkoxyphenyl units to the para positions of 2-methoxy-4,6-diphenylnicotinonitrile core via olefin bonds. The effect of terminal linear chains (like hexyloxy, octyloxy, and hexadecyloxy chains) on their photophysical (solvatochromism and aggregation induced emission (AIE)) and electrochemical properties were systematically investigated. All the compounds exhibit strong solvatochromism and only the compounds bearing lower alkoxy chains (i.e. hexyloxy and octyloxy chains) shows the AIE behavior. Further, the electrochemical studies shows that the compounds possess a band gap of similar to 2.26 eV with deep-lying highest occupied molecular orbital (HOMO) energy level at similar to-5.94 eV and lowest unoccupied molecular orbital (LUMO) energy level at similar to-3.70 eV. From the literature, it was noted that the observed frontier energy values of these compounds are encouragingly matching to the frontier energy values of perylene diimide (PDI) and indandione derivative based non-fullerene acceptors, thus, these compounds pave the way for their potential applications in solar cells.

Versatile conjugated small molecules bearing cyanopyridone core (CP1–5), composed of various donor/acceptor moieties at position −4 and −6 have been designed, developed and characterized. Their solvatochromic studies were conducted and analyzed using Lippert-Mataga, Kamlet-Taft and Catalan solvent scales and interesting results were obtained. The polarizability/dipolarity of the solvent greatly influenced the spectra. The electrochemical studies were carried out using cyclic voltammetry to calculate the HOMO-LUMO energy levels. The study revealed that the synthesized conjugated small molecules possess low lying HOMO energy levels which can be exploited for application in various fields of optoelectronics.