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Introducing upconversion nanoparticles (UCNPs) onto photoanode films is an effective way to enhance the photovoltaic performance of dye-sensitized solar cells (DSSCs). In this contribution, the β -NaYGdF 4 :Yb, Er UCNPs and β -NaYGdF 4 :Yb,Er@SiO 2 nanoparticles (NPs) were prepared by tuning the dopant contents of the Gd ions and the β -NaYGdF 4 :Yb,Er@SiO 2 NPs were applied as an upconverting layer in DSSCs. Upconversion photoluminescence indicates that the UCNPs doped with 5% Gd ions exhibit the strongest green and red fluorescence emissions. Moreover, the DSSCs device incorporating the NPs with 5% Gd ion dopant can achieve an optimal photovoltaic efficiency of 5.89%, which is 20.20% enhancement in comparison to the device without NPs and 16.17% increasement with respect to the device containing β -NaYF 4 :Yb,Er@SiO 2 nanocrystals, thus highlighting the effect of the doping of the Gd ions in nanoparticles on their upconversion photoluminescence and photoelectric performance. Accordingly, the current results offer a feasible strategy for further regulating the photoluminescence property of UCNPs and optimizing the photovoltaic performance of UCNPs-based DSSCs devices. [Display omitted] • Two kinds of Gd-doped nanoparticles are prepared and applied to dye-sensitized solar cells. • The UCNPs doped with 5% Gd ion exhibit the strongest green and red fluorescence emissions. • The DSSCs containing the UCNPs with 5% Gd dopant can achieve a best photovoltaic performance. • The current results offer a feasible strategy for further regulating the upconversion photoluminescence of UCNPs. • This work provides an insight into possible further optimization of the efficiency of UCNPs-based DSSCs. [ABSTRACT FROM AUTHOR]

• A synergistic effect of upconversion nanoparticles (UCNPs) and TiO 2 hollow spheres (TiO 2 -HSs) was explored. • An optimal PCE of 8.17% was achieved in the DSSCs containing the UCNPs and TIO 2 -HSs. • This work opens a new way of preparing composite photoanode films to improve the photovoltaic performances of DSSCs. Introducing upconversion nanoparticles (UCNPs) or fabricating TiO 2 hollow spheres (TiO 2 -HSs) are considered two feasible strategies to enhance the photovoltaic performance of dye-sensitized solar cells (DSSCs). However, studies investigating a combination of UCNPs and TiO 2 -HSs for the application in DSSCs are still scarce. In this contribution, NaYF 4 :Yb,Er@NaGdF 4 :Nd@SiO 2 UCNPs and TiO 2 -HSs were synthesized and respectively applied as upconversion layers and scattering layers on the TiO 2 photoanode of DSSCs. The influence of different doping ratios of UCNPs on cell performance was explored. The present results reveal that the DSSCs device based on conventional P25 photoanode films incorporating the UCNPs with 10% can achieve a photovoltaic efficiency of 6.65%, showing 29.63% enhancement in comparison to the device without UCNPs. When the TiO 2 -HSs are used as scattering layers above the P25 film, the DSSCs device obtains a higher photovoltaic efficiency of 6.97%. More importantly, combining the UCNPs and TiO 2 -HSs can further enhance the photoelectrical property of DSSCs, realizing an optimal efficiency of 8.17%. Such an improvement can be attributed to a synergistic mechanism arising from the upconversion effect of UCNPs and the light scattering effect of TiO 2 -HSs. This work opens a new way of preparing composite photoanode films to improve the photovoltaic performances of DSSCs. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • This study theoretically reveals the impact of rigidly fused π-bridge on the photovoltaic efficiency of organic dyes. • Introducing strong electron-withdrawing group can enhance the photovoltaic performance of the dye molecule. • This work provides a useful guidance for designing highly-efficient dye sensitizers by molecular engineering. The influence of different types of π-bridges in triphenylamine-based organic sensitizers on their photophysical and photovoltaic properties is investigated by using sophisticated first-principles calculations and reliable theoretical models. Two well-designed strategies, namely the cyclization between separate benzothiadiazole and bithiophene as well as the insertion of electron-rich/deficient groups between the rigidly fused π-bridge and anchor moieties are proposed. It is found that the calculated photophysical and photovoltaic parameters of the dye with an unfused π-bridge reproduce very well the available experimental data, ensuring the rationality of present theoretical methods and models. The designed dye featuring a rigidly fused π-bridge shows a remarkable decrease of power conversion efficiency (PCE), with respect to the dye with an unfused π-spacer (6.36% vs. 11.18%), which implies that simply cyclizing separate aromatic heterocyclic groups is unfavorable for improving the photoelectrical performance. However, the PCE can be increased to 14.20% when an electron-rich thiophene group is introduced between the fused π-bridge and the anchor units. More importantly, replacing the thiophene moiety with an electron-deficient benzothiadiazole group can further improve the photovoltaic performance, and consequently a PCE as high as 23.81% is achieved, which is a significant theoretical improvement for triphenylamine-based organic dyes. To sum up, this study theoretically elucidates the effect of unfused and fused π-bridges as well as the introduction of electron-rich/deficient groups in organic dyes on their photophysical and photoelectric properties and provides a useful guidance for further designing highly-efficient dye sensitizers by molecular engineering. [ABSTRACT FROM AUTHOR]

In this work, the single and double proton transfer dynamic process in the first excited state of 2,5-bis(2-benzothiazolyl)hydroquinone (BBTHQ) were theoretically investigated based on the time-dependent density functional theory (TD-DFT) method. The calculations of primary bond lengths, bond angles, IR vibrational spectra and NCI analysis reveal that two intramolecular hydrogen bonds of BBTHQ are strengthened in the first excited state, which provides a driving force for excited state proton transfer. The frontier molecular orbitals (FMOs) indicate the nature of intramolecular charge transfer. In addition, the potential energy surfaces (PESs) of the ground state and first excite state were also constructed to further elucidate the mechanism of intramolecular proton transfer of BBTHQ. [ABSTRACT FROM AUTHOR]