Grain boundaries in bulk perovskite films are considered as giant trapping sites for photo-generated carriers. Surface engineering via inorganic perovskite quantum dots has been employed for creating monolithically grained, pin-hole free perovskite films.

Two brilliant outcomes of supramolecular self-assembly directed, low molecular weight organic gelator based self-healable Co(II) and Ni(II) metallogels were achieved. The adipic acid as the low molecular weight organic gelator...

Simultaneous occurrence of saturable absorption nonlinearity and two-photon absorption nonlinearity in the same medium is well sought for the devices like optical limiter and laser mode-locker. Pristine graphene sheet consisting entirely of sp2-hybridized carbon atoms has already been identified having large optical nonlinearity. However, graphene oxide (GO), a precursor of graphene having both sp2 and sp3-hybridized carbon atom, is increasingly attracting cross-discipline researchers for its controllable properties by reduction of oxygen containing groups. In this work, GO has been prepared by modified Hummers method, and it has been further reduced by infrared (IR) radiation. Characterization of reduced graphene oxide (RGO) by means of Raman spectroscopy, X-ray photoelectron spectroscopy, and UV-Visible absorption measurements confirms an efficient reduction with infrared radiation. Here, we report precise control of non-linear optical properties of RGO in femtosecond regime with increased degrees of IR reduction measured by open aperture z-scan technique. Depending on the intensity, both saturable absorption and two-photon absorption effects are found to contribute to the non-linearity of all the samples. Saturation dominates at low intensity (∼127 GW/cm2) while two-photon absorption becomes prominent at higher intensities (from 217 GW/cm2 to 302 GW/cm2). The values of two-photon absorption co-efficient (∼0.0022–0.0037 cm/GW for GO, and ∼0.0128–0.0143 cm/GW for RGO) and the saturation intensity (∼57 GW/cm2 for GO, and ∼194 GW/cm2 for RGO) increase with increasing reduction, indicating GO and RGO as novel tunable photonic devices. We have also explained the reason of tunable nonlinear optical properties by using amorphous carbon model.

Two protein-based self-healing Cu(II)-metallohydrogels named BSA-CuA and BSA-CuCl have been synthesized by mixing acetate and chloride salts of Cu(II) distinctly with the protein bovine serum albumin (BSA) in water medium. Experimentally investigated rheological parameters of both synthesized metallohydrogels not only expose the viscoelastic semi solid nature and mechanical toughness but also reveal the self-healing properties of both metallohydrogel materials. Counteranion-directed morphological variations of these metallohydrogels are visualized through field-emission scanning electron microscopic images. The third-order optical nonlinear susceptibility x (3) of these synthesized metallohydrogels has been studied using the Z-scan technique at a wavelength of 550 nm under the femtosecond regime in the excitation intensity range from 66 to 283 GW/cm 2 . BSA-CuA and BSA-CuCl metallohydrogels exhibit a high value of the positive nonlinear refractive index n 2 I and two-photon absorption coefficient β eff , which are very important for all-optical switching, optical limiting, and other photonic applications. The polarity possibly associated with the self-healing property of these two synthesized metallohydrogels has been justified through the experimentally measured high value of optical nonlinearity. At 88 GW/cm 2 intensity of the excitation beam, the n 2 I values for BSA-CuA and BSA-CuCl are (14.40 ± 0.16) × 10 −7 cm 2 /GW and (10.99 ± 0.15) × 10 −7 cm 2 /GW, respectively, and at 283 GW/cm 2 intensity, the β eff values are (0.0662 ± 0.0002) cm/GW and (0.0540 ± 0.0001) cm/GW, respectively. The (x (3) ) of BSA@CuA and BSA@CuCl at 283 GW/cm 2 is (1.757 ± 0.018) (esu ×10 −14 ) and (1.560 ± 0.017) (esu ×10 −14 ), respectively.

The ambient stability, hysteresis, and trap states in organo-halide perovskite solar cells (PSCs) are correlated to the influence of interlayer interfaces and grain boundaries. Astute incorporation of Cu2ZnSnS4 (CZTS) and Au/CZTS core/shell nanocrystals (NCs) can realize the goal of simultaneously achieving better performance and ambient stability of the PSCs. With optimized Au/CZTS NC size and concentration in the photoactive layer, power conversion efficiency can be increased up to 19.97 ± 0.6% with ambient air stability >800 h, as compared to 14.46 ± 1.02% for the unmodified devices. Through efficient carrier generation by CZTS and perovskite, accompanied by the plasmonic effect of Au, carrier density is sufficiently increased as validated by transient absorption spectroscopy. NCs facilitate the interfacial charge transfer by suitable band alignment and removal of recombination centers such as metallic Pb0, surface defects, or impurity sites. NC embedding also increases the perovskite grain size and assists in pinhole filling, reducing the trap state density.