Search

Developing highly efficient small molecule hole-transporting materials (HTMs) to improve the performance of devices is one of the hot topics in the progress of perovskite solar cells (PSCs). In this work, a series of molecules are designed by utilizing benzocyclobutadiene (C1), bicyclo[6.2.0]decapentaene (C2), naphthalene (C3), biphenylene (C4), fluorene (C5), and azulene (C6) as the π-cores, and p-methoxydiphenylamine (R1), p-methoxytriphenylamine (R2) and p-methoxydiphenylamine-substituted carbazole (R3) as the peripheral groups. For isolated molecules, frontier molecule orbitals, absorption and emission spectra, Stokes shift, stability, solubility, and hole mobility are assessed by density functional theory calculations along with the Marcus theory of electron transfer. The molecules adsorbed on the surface of CH3NH3PbI3 are used to simulate the interfacial properties between HTMs and perovskites. Our results indicate that varying the central bridge and the terminal groups has a remarkable influence on the properties. The designed R2-Cn (n = 3, 4, 5) have deeper HOMO levels, stronger absorption in the UV region, and larger Stokes shift than Spiro-OMeTAD. They also possess good solubility, stability, and hole mobility. The proper alignment of interfacial energy levels ensures the transfer of holes from CH3NH3PbI3 to the studied molecules and blocks the backflow of electrons simultaneously. Significant charge redistributions around the interfacial region benefit the separation and transfer photogenerated electron–hole pairs. The results of the present study can be further employed in the process of synthesizing new HTMs with promising features. [ABSTRACT FROM AUTHOR]

We present here the influence of different surface terminations on the electronic, optical, and photocatalytic properties of trans and cis BaTaO2N using density functional theory calculations. For each surface, we consider two complementary terminations exposed with Ba and Ta atoms, respectively. The calculated surface energies suggest that (001) and (100) are more stable than other low-index surfaces. Work functions are distinct for various surface terminations, which can be attributed to the atomic displacements in different directions and degrees after relaxation. We propose that the transferring direction of the photogenerated carriers in BaTaO2N-based heterostructures could be controlled by obtaining the preferred surface termination. The simulated absorption spectra suggest that both trans and cis BaTaO2N exhibit optical anisotropy, which could result from the difference in relaxed crystal parameters along different directions. Dissociative water adsorption on both the (001) and (100) terminations is thermodynamically favorable. The hydrogen evolution reaction (HER) is easier to occur on the terminations exposed with Ta, O, and N simultaneously. The computed overpotentials of oxygen evolution reaction (OER) for trans-(001)-BaO, cis-(001)-TaON, cis-(001)-BaO, and cis-(100)-Ta2O3N are in good agreement with the experimental results. These findings provide important insights into the rational design of (001)- and (100)-oriented BaTaO2N samples for enhanced photocatalytic activity. [ABSTRACT FROM AUTHOR]

Density functional theory calculations are applied to study the influence of co-doping on the stability, electronic structure, and photocatalytic activity of tetragonal BaTiO 3 (001) surface. The results show that the formations of all the metal-nonmetal co-doped BaTiO 3 (metal = V, Nb, Ta, Mo, W and nonmetal = N, C) are energetically favorable. Most of co-doped surfaces have remarkable narrower bandgaps than the pristine surface, which favors the movement of absorption edge to the visible light region. Co-doped systems have better affinity toward H 2 O than the pure surface. For most of the studied systems, the active sites of HER and OER are the O site and the Ti site adjacent to the metal dopant, respectively. Surface co-doping results in remarkable decreases in | Δ G H | of HER and the OER overpotential of BaTiO 3 (001) surface. This work proposes the potential application of BaTiO 3 modified by surface co-doping as efficient photocatalysts for overall water splitting. Surface codoping in BaTiO 3 remarkably enhances the activities of HER and OER. [Display omitted] • Surface codoping can efficiently reduce the band gap of BaTiO 3. • Co-doped BaTiO 3 surfaces have better affinity toward H 2 O than the pure one. • Co-doped BaTiO 3 involving Mo or W remarkably improve the OER performance. • Co-doped surfaces exhibit higher activities in HER than the pure BaTiO 3 surface. [ABSTRACT FROM AUTHOR]

Codoping with cations and anions is found to be an effective approach to tailor the electronic structures of semiconductor-based photocatalysts. In this work, a systematic hybrid density functional study has been carried out for BaTiO3 with a wide bandgap, codoped with TM and X (TM = V, Nb, Ta, Mo and W, X = N and C), with the objective of improving its photocatalytic activity for water splitting under visible light irradiation. Oxygen-rich conditions are found to be more favorable for the synthesis of the (TM + X)-codoped materials, and under these conditions, the formation energy for the codoped BaTiO3 is even lower than that of the TM-monodoped system. A smaller deformation of the BaTiO3 crystal structure corresponds to a more favorable formation of (TM + X)-codoped systems. Passivated codoping is found to be advantageous because it effectively reduces the band gap without encountering any localized impurity states observed in the related monodoped systems. The band alignments for all the codoped systems are well positioned for the feasibility of both photooxidation and photoreduction of water. It is found that there are seven investigated systems with bandgaps smaller than 3 eV. Among them, passivated codoped systems including Mo and W have been found to be the most effective for narrowing the bandgap (Eg is in the range of 1.55–2.16 eV), increasing the mobilities of photoinduced carriers and improving the photocatalytic activity of BaTiO3 under visible light. These materials are promising photocatalysts for overall water splitting under visible-light irradiation and further experimental investigations are highly demanded to explore their potential applications in the photocatalytic field. [ABSTRACT FROM AUTHOR]

NaTaO 3 loaded with NiO cocatalyst is one of the few photocatalysts for overall water splitting in UV region, which have attracted much attention. In this work, density functional theory calculations have been performed to investigate the interfacial geometries, electronic structures, charge transport, optical absorptions and band offsets of NiO(001)/NaTaO 3 (001) slab models. By considering possible terminations of NaTaO 3 (001) surface, two heterostructures denoted as NiO/TaO 2 and NiO/NaO have been constructed. Our results show that two kinds of contact are thermodynamically stable, and there is a stronger rumpling of atomic layers appearing in NiO/NaO than NiO/TaO 2. The calculated band structures reveal that NiO(001)/NaTaO 3 (001) interfaces have indirect band gaps. The mobilities of photoinduced charge carriers in interfacial structures are faster than those in pure surfaces. NiO/TaO 2 has a higher mobility and lower recombination rate of photogenerated electrons and holes than NiO/NaO. Loading NiO on NaTaO 3 surface has a negligible effect on the extension of light absorption, which is consistent with experiments. Both heterostructures form a Type-II band alignment. The difference of electrostatic potentials around the interface as a driving force boosts the migration of electrons and holes to different domains of the interface, which is beneficial to extend the lifetime of photoinduced carriers and improve the photocatalytic activity of NaTaO 3 system. NiO/TaO 2 has the ability of overall splitting water with NiO as the oxidation cocatalyst, while in NiO/NaO, the photogenerated electrons and holes are accumulated on NiO and NaO side, respectively. Our results demonstrate that the function of NiO in NiO/NaTaO 3 photocatalytic system is determined by the termination property of NaTaO 3 (001) surface, which may be one possible reason why it is difficult to ascertain whether NiO is a proton reduction cocatalyst or water oxidation cocatalyst experimentally. • The heterostructures have indirect gaps and faster mobilities of charge carriers. • The interface benefits the separate gathering of charge carriers on two components. • The different electrostatic potentials is a driving force for charge separation. • The contacting layer of NaTaO 3 (001) with NiO(001) is the key to the role of NiO. • Our findings give reasonable explanations on the high activity of NiO/NaTaO 3. [ABSTRACT FROM AUTHOR]

Designing high-performance hydrogen evolution reaction (HER) catalysts is crucial for seawater splitting. Herein, we demonstrate a facile Anderson-type polyoxometalate-assisted synthesis route to prepare defect-rich doped 1T/2H-MoSe 2 nanosheets. As demonstrated, the optimized defect-rich doped 1T/2H-MoSe 2 nanosheets display low overpotentials of 116 and 274 mV to gain 10 mA cm -2 in acidic and simulated seawater for the HER, respectively. A magnesium (Mg)/seawater battery was fabricated with the defect-rich doped 1T/2H-MoSe 2 nanosheet cathode, displaying the highest power density of up to 7.69 mW cm -2 and stable galvanostatic discharging over 24 h. The theoretical and experimental investigations show that the superior HER and battery performances of the heteroatom-doped MoSe 2 nanosheets are attributed to both the improved intrinsic catalytic activity (effective activation of water and favorable subsequent hydrogen desorption) and the abundant active sites, benefiting from the favorable catalytic factors of the doped heteroatom, 1T phase, and defects. Our work presents an intriguing structural modulation strategy to design high-performance catalysts toward both HER and Mg/seawater batteries.