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The hexagonal NiCo2S4 hierarchical nanostructure was nucleated on the reduced graphene oxide (rGO) sheets using a simple hydrothermal method for use it as an electrode material for supercapacitor applications. Benefiting the synergistic effects from the hierarchical architecture of NiCo2S4 and outstanding conductivity of rGO, the hybrid rGO-NiCo2S4 composites provided many advantages such as increased electrolyte diffusion pathways, fast electron transport, and ample active sites. Thus, the hybrid rGO-NiCo2S4 composites presented a higher specific capacitance (972 F/g), compared with bare NiCo2S4 (716 F/g), at the current density of 1 A/g. Using the prepared nanomaterials, the asymmetric supercapacitor devices were constructed in the form of the 2-electrodes scheme. Remarkably, the rGO-NiCo2S4 based device demonstrated the excellent energy-storage characteristics with a higher specific capacitance (208 F/g) than that of the bare NiCo2S4 based device (86 F/g). After 2000 cycles, the rGO-NiCo2S4 supercapacitor device revealed an excellent cyclic stability with 94.1% of the capacitance retention at the current density of 3 A/g. Moreover, hybrid rGO-NiCo2S4 showed an admirable catalytic activity for nitroarene reduction. These findings suggest that the prepared rGO-NiCo2S4 MOF can be served as an excellent bifunctional electrocatalyst for the high-performance supercapacitor and the nitroarene reduction applications.

Luminescent solar concentrators (LSCs) provide a transformative approach to integrating photovoltaics into a built environment. In this paper, we report thin-film LSCs composed of intramolecular charge transfer fluorophore (DACT-II) and discuss the effect of two polymers, polymethyl methacrylate (PMMA), and poly (benzyl methacrylate) (PBzMA) on the performance of large-area LSCs. As observed experimentally, DACT-II with the charge-donating diphenylaminocarbazole and charge-accepting triphenyltriazine moieties shows a large Stokes shift and limited re-absorption losses in both polymers. Our results show that thin-film LSC (10 × 10 × 0.3 cm3) with optimized concentration (0.9 wt%) of DACT-II in PBzMA gives better performance than that in the PMMA matrix. In particular, optical conversion efficiency (ηopt) and power-conversion efficiency (ηPCE) of DACT-II/PBzMA LSC are 2.32% and 0.33%, respectively, almost 1.2 times higher than for DACT-II/PMMA LSC.

The steric shielding offered by sensitizers on semiconducting surfaces as a result of branching in the dyes used offers the less utilization of semiconducting substrate sites during device fabrication in dye-sensitized solar cells (DSSCs). This work proposes a strategy to increase the coverage through the utilization of small molecules which have the ability to penetrate into the sites. The small molecules play the dual role of vacancy filling and sensitization, which can be viewed as an alternative to co-sensitization also. Hence, we show for the first time ever that the co-adsorption of catechol with Z907 as a sensitizer enhances the electron density in the photo-anode by adsorbing on the vacant sites. Catechol was subsequently adsorbed on TiO2 after Z907 as it has a stronger interaction with TiO2 owing to its favorable thermodynamics. The reduced number of vacant sites, suppressed charge recombination, and enhanced spectral response are responsible for the improvement in the PCEs. Quantitatively, both organic and aqueous electrolytes were used and the co-sensitized DSSCs had PCE enhancements of 7.2 and 60%, respectively, compared to the control devices.

The co-sensitization of dye sensitizers has been demonstrated as a potential way to improve the efficiency of DSSC, because of its positive effects such as reducing dye aggregation on TiO2 surface, suppressing charge recombination, and improving the open circuit voltage. In this work, we realized that the co-adsorption of ruthenium based N719 dye and organic D35 dye has enhanced the electron relaxation lifetime, carrier concentration, and charge separation in TiO2 photoanode, thus improving the performance of DSSCs. The high efficiency of 8% was obtained in DSSC with dye co-sensitization than its single dye based DSSCs (6.9% for N719 and 6.5% for D35).

An emerging important class of photovoltaics for the next generation, the dye sensitized solar cells (DSSCs) has attracted great attention due to its low-cost, simple fabrication process and good performance. Though, one of the major loss mechanisms leads to lowering the power energy conversion efficiency is thermalization of charge carriers generated by the absorption of high energy photons. One promising novel strategy to decrease such thermalization loss is the use of downconversion (DC) luminescent materials as spectral converters. The rare-earth doped downshifting materials can converts higher energy photons into lower energy photons based on energy transfer from lanthanide ions to Yb3+ ions. In addition, the downconversion nanoparticles (DCNPs) are also act as scattering centers which can facilitates the light capture in photo-absorbing layer. With this aim, the rare earth doped downconversion SrF2: Pr3+-Yb3+ nanoparticles were synthesized by facile template free hydrothermal method. X-ray diffraction analysis confirms the formation cubic SrF2 phase. The prepared SrF2: Pr3+-Yb3+ down-shifting nanophosphor shows strong absorption in UV region and broad luminescence band emission in visible region evidenced from absorption and photoluminescence studies respectively. The enhancement in power conversion efficiency (PCE) was achieved by employing the synthesized downconverting nanomaterial as bottom layer in DSSC photoanode (Fig.1). The photovoltaic performance of the device was studied using standard solar simulator at 1 Sun intensity (AM 1.5 G) and DSSC with SrF2: Pr3+-Yb3+ shows improved efficiency of 9.066% than bare TiO2 based device (8.395%). The down-shifting nanophosphor material enhanced the efficiency of DSSC by 7.4% with 7.5% increment in photocurrent density compared to bare TiO2 based device. Figure 1