We have systematically explored how plasmonic effects influence the characteristics of polymer photovoltaic devices (OPVs) incorporating a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). We blended gold nanoparticles (Au NPs) into the anodic buffer layer to trigger localized surface plasmon resonance (LSPR), which enhanced the performance of the OPVs without dramatically sacrificing their electrical properties. Steady state photoluminescence (PL) measurements revealed a significant increase in fluorescence intensity, which we attribute to the increased light absorption in P3HT induced by the LSPR. As a result, the rate of generation of excitons was enhanced significantly. Furthermore, dynamic PL measurements revealed that the LSPR notably reduced the lifetime of photogenerated excitons in the active blend, suggesting that interplay between the surface plasmons and excitons facilitated the charge transfer process. This phenomenon reduced the recombination level of geminate excitons and, thereby, increased the probability of exciton dissociation. Accordingly, both the photocurrents and fill factors of the OPV devices were enhanced significantly. The primary origin of this improved performance was local enhancement of the electromagnetic field surrounding the Au NPs. The power conversion efficiency of the OPV device incorporating the Au NPs improved to 4.24% from a value of 3.57% for the device fabricated without Au NPs.

In the current study, the nanocomposite of molybdenum disulfide and multi-walled carbon nanotubes (MWCNT@MoS 2 ) was proposed for the first time as a counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I 3 À ) to iodide (I À ). This novel catalyst was synthesized by simply mixing MWCNTs and MoS 2 in an acidic solution and then converting the solid intermediate into the MWCNT@MoS 2 nanocomposite in a H 2 flow at 650 C. X-ray powder diffraction, Raman and X-ray photoemission spectroscopy confirmed the composition and the structure of the MWCNT@MoS 2 nanocomposite. The microstructure details of the nanocomposite were studied by transmission electron microscopy, showing that only a few-layers of the MoS 2 nanosheets were formed on the MWCNT surface. This unique structure is beneficial to the improvement of the catalytic activity of MWCNT@MoS 2 towards the reduction of I 3 À. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MWCNT@MoS 2 CE was higher than those of MoS 2 , MWCNT and sputtered Pt CEs due to the increased active surface area of the former. Moreover, the peak current densities of the MWCNT@MoS 2 CE showed no sign of degradation after consecutive 100 CV tests, suggesting the great electrochemical stability of the MWCNT@MoS 2 CE. Furthermore, the MWCNT@MoS 2 CE demonstrated an impressive low chargetransfer resistance (1.69 U cm 2 ) for I 3 À reduction. Finally, the DSSC assembled with the MWCNT@MoS 2 CE showed a high power conversion efficiency of 6.45%, which is comparable to the DSSC with Pt CE (6.41%).

In this study, we have explored how light trapping efficiency can be enhanced by using gold nanoparticles (Au NPs) of various sizes and shapes on the front of polymer solar cells (PSCs) with the active layerblends of poly(3-hexyl thiophene) and [6,6]-phenyl-C 61 -butyric acid methyl ester. The light-concentrating behavior was enhanced after we had incorporated gold nanospheres or nanorods into the anodic buffer layer [based on poly (3,4-ethylenedioxythiophene):polystyrenesulfonate] to trigger various localized surface plasmon resonance (LSPR) bands. Comparison of the optical characteristics and the performance of the PSCs prepared with and without Au NPs, and we found that the UV−vis and wavelength-dependent photoluminescent spectral data corroborated with the device performance due to the photon management by considering the light scattering and LSPR effects at the active layer. The presence of Au NPs increased the power conversion efficiency to approximately 4.3% (an enhancement of 24%). ■ INTRODUCTIONPolymer solar cells (PSCs) are promising technologies of utilizing renewable energy for mass production because of their lightweight and cost-effective production with simple processability. At present, the best power conversion efficiencies (PCEs) of bulk heterojunction (BHJ) PSCs have reached 6− 8% under AM 1.5G conditions. 1−3 After optimizing the thickness and morphology of the donor−acceptor interface of a blended film, consisting of a semiconducting polymer as the donor and a soluble fullerene as the acceptor, a BHJ photoactive layer having a thickness of approximately 200 nm would provide a high fill factor (FF) and an enhanced possibility of exciton dissociation and electrical transportation. 4−6 Furthermore, low-bandgap (LBG) materials can be used to further enhance the device performance by extending the absorption region to longer wavelength. 7−9 Although LBG materials are often associated with lower hole mobilities than are conventional poly(3-hexylthiophene) (P3HT) materials, these charge-transport problems can be overcome by decreasing the thickness of the photoactive layer, albeit with lower external quantum efficiencies (EQEs). Therefore, it is necessary to develop light-concentrating systems to enhance the light trapping efficiency of thinner active layers, especially for use in normal PSC device architectures.Recently, plasmonic light trapping has been applied to effectively enhance the light harvesting performance of solar cells, featuring either continuous metal films [through the excitation of surface plasmon polaritons (SPPs)] or metal nanoparticles [through scattering or localized surface plasmon resonance (LSPR) effects]. 10−18 In PSC devices using SPPs, the electromagnetic wave propagating along the interface between the active layer and back contact electrode should result in higher light trapping efficiency. The short-range EQE enhancement was observed, however, only at a certain excitation wavelength, which was related to the distance and height of the periodic grating structures of th...

In the current study, a nanocomposite of molybdenum disulfide and graphene (MoS 2 /RGO) was proposed for the first time as the counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I 3 À ) to iodide (I À ). This novel catalyst was synthesized by simply mixing graphene oxide nanosheets with a solution of ammonium tetrathiomolybdate and then converting the solid intermediate into MoS 2 /RGO nanocomposite in a H 2 flow at 650 C. Atomic force microscopy, X-ray powder diffraction and X-ray photoemission spectroscopy confirmed that MoS 2 nanoparticles were deposited onto the graphene surface. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MoS 2 /RGO CE was higher than those of MoS 2 , RGO and sputtered Pt CEs, due to the increased active surface area of the former. Moreover, the peak current densities of the MoS 2 /RGO CE showed no sign of degradation after 100 consecutive CV tests, suggesting the great electrochemical stability of the MoS 2 /RGO CE. Furthermore, the MoS 2 /RGO CE demonstrated an impressively low charge-transfer resistance (0.57 U cm 2 ) for I 3 À reduction. Finally, the DSSC assembled with the MoS 2 /RGO CE showed a high power conversion efficiency of 6.04%, which is comparable to the DSSC with a Pt CE (6.38%).

Here, we report the facile preparation of tunable magnetic Ni-doped near-infrared (NIR) quantum dots (MNIR-QDs) as an efficient probe for targeting, imaging, and cellular sorting applications. We synthesized the MNIR-QDs via a hot colloidal synthesis approach to yield monodisperse and tunable QDs. These hydrophobic QDs were structurally and compositionally characterized and further functionalized with amino-PEG and carboxyl-PEG to improve their biocompatibility. Since QDs are known to be toxic due to the presence of cadmium, we have evaluated the in vitro and in vivo toxicity of our surface-functionalized MNIR-QDs. Our results revealed that surface-functionalized MNIR-QDs did not exhibit significant toxicity at the concentrations used in the experiments and are therefore suitable for biological applications. For further in vitro applications, we covalently linked folic acid to the surface of amino-PEG-coated MNIR-QDs through NHS chemistry to target the folate receptors largely present in the HeLa cells to demonstrate the specific targeting and magnetic behavior of these MNIR-QDs. Improved specificity has been observed with treatment of HeLa cells with the folic acid-linked amino PEG-coated MNIR QDs (FA-PEG-MNIR-QDs) compared to the one without folic acid. Since the synthesized probe has magnetic property, we have also successfully demonstrated sorting between the cells which have taken up the probe with the use of a magnet. Our findings strongly suggest that these functionalized MNIR-QDs can be a potential probe for targeting, cellular sorting, and bioimaging applications.

No abstract

No abstract

An energy upconversion system based on triplet-triplet annihilation exploiting an organic triplet sensitizer is devised and has achieved a white-light emission with a low power laser excitation.