No abstract

Dye-sensitized solar cells (DSSCs) remain a promising technology for clean energy conversion due to their low cost, simple manufacturing, and high scalability. However, to keep these devices competitive against other photovoltaics like organic (OSCs) and perovskite solar cells (PSCs), it is necessary to enhance their efficiency. These improvements can be achieved by optimizing the charge transport and non-radiative carrier recombination within the operating device. Here, we show the design, fabrication, and subsequent characterization of Ti 3 C 2 T x MXene/TiO 2 nanocomposite hybrid photoanodes, supported by computational modeling. Ti 3 C 2 T x MXene/TiO 2 hybrid photoanodes containing 0.050, 0.075, and 0.100 wt % two-dimensional (2D) Ti 3 C 2 T x flakes were prepared and investigated. The power conversion efficiency (PCE) of the device is found to be enhanced by 20% when only 0.075 wt % Ti 3 C 2 T x was added to TiO 2 due to the increase of electron transport in the photoanode. The density functional theory (DFT) calculations of the MXene−TiO 2 interface indicate that the anatase potential is lowered, thus increasing the energy difference between the conduction bands of the N719 dye and the nanocomposite and favoring the migration of electrons toward the output terminal. Moreover, DFT results suggest a better separation of the photocarriers at the nanocomposite−N719 interface, which is supported by the measurement of longer electron lifetimes in the photoanode. These features demonstrate that the introduction of Ti 3 C 2 T x into the photoanode is relevant to promote the energy-to-current conversion of DSCCs. Future approaches shall focus on the implementation of different 2D MXene structures to further improve the performance of these class of materials for direct applications in photovoltaic devices and photochemistry.

Perovskite oxide heterostructures have been extensively investigated for their excellent photocatalytic properties. Here, through hybrid density functional theory calculations, we systematically investigate the formation of NaNbO 3 −NaTaO 3 (NBO-NTO) heterostructures. The sequential cations replacement in the superlattices reveals the Nb−Ta ratio range that allows the effective formation of heterostructures, which occurs through a spontaneous polarization mechanism induced by the electrostatic potential discontinuity in the interface. The resulting cation ordering is responsible for the sawtoothlike potential distribution that spatially separates valence and conduction charges and reduces the heterostructure bandgap. The symmetric NBO 5 /NTO 5 junction has the smallest bandgap (2.50 eV) whose transitions are associated with Nb 5d xy orbitals on the interfacial plane. Such a relaxation mechanism provides the heterostructure with anisotropic optical properties and interface absorption peaks closer to the visible light spectrum. The phenomena strongly suggest the use of these heterostructures in photocatalytic reactions, supported by their coherent band-edge alignment with both water splitting and CO 2 reforming potentials.

Sodium tantalate 1-D nanostructures show novel properties due to their edge confinement region, which may be relevant for distinct applications.