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The investigation of adsorption properties of anchor group on photo-anode is foundation in the optimization of dye sensitizers (DS) for solar cells. α-cyanoacrylic acid (CAA) is the typical anchor moiety coupled electronic acceptor in DS. To understand the interaction between rutile TiO 2 photo-anode and DS based upon CAA in dye sensitized solar cells, the atomic configurations, energies and electronic properties of CAA adsorbed on rutile TiO 2 (1 1 0) surface were studied by using density functional theory calculations. The results indicate CAA prefers to dissociatively adsorb on rutile TiO 2 (1 1 0) surface as bidentate configuration in which the O atoms of CAA bind with two adjacent surface five-coordinate Ti atoms along [0 0 1] direction, and the H atom in hydroxyl of CAA adhere to the nearest neighbor surface O atom at bridge site, generating a hydroxyl species. The corresponding adsorption energy is 1.480 eV. The analysis of geometrical parameters, density of states and electron density suggests the bonds between rutile TiO 2 (1 1 0) surface and CAA are formed. The density of states and orbital character at the gamma-point in reciprocal space support that the adsorption of CAA on the surface provides feasible mode for photo-induced electron injection. [ABSTRACT FROM AUTHOR]

( MgO ) 9 with a rocksalt structure, a magic number cluster of ( MgO ) n , exhibits high stability. In this study, the hydrogen storage properties of ( MgO ) 9 under an external electric field are explored by DFT calculation. The results reveal that H 2 can be adsorbed on single Mg/O atoms. Because the ( MgO ) 9 and H 2 are effectively polarized by the external electric field, the adsorption strength of H 2 at certain adsorption sites is substantially enhanced. The adsorption energies of H 2 on three-coordinated Mg/O atoms increase from −0.071/−0.056 eV in the absence of an electric field to −0.186/−0.237 eV under a field intensity of 0.025 a.u. Under the field, ( MgO ) 9 can adsorb a maximum of 18 H 2 molecules, and the corresponding mass density of hydrogen storage reaches 9.1 wt%. Our results suggest that subjecting the ( MgO ) 9 to an external electric field is a potential hydrogen storage method. In this paper, the interaction mechanism between H 2 and ( MgO ) 9 under the external electric field is also investigated through an electronic structure analysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] Selecting DFT functional is important to calculate the excited state properties. [•] The excited states with not-effective charger transfer character result into smaller Jsc . [•] The designed Ru-complexes may have good performance in DSCs. [Copyright &y& Elsevier]

Abstract: Genetic algorithm was combined with the semi-empirical quantum chemical PM3 method (GA+PM3) to scan the potential energy surface of cluster. The resulting isomers found by the GA+PM3 approach were then further optimized at the first principle level using Density Functional Theory (DFT) to obtain the optimal geometry and electronic structure for each cluster. This methodology was applied to investigate Si6N8 clusters. The electric charges and bond properties, along with the IR and Raman frequencies, polarizabilities and hyperpolarizabilities, of Si6N8 clusters were analyzed in detail. [Copyright &y& Elsevier]

The morphology of donor‐acceptor heterojunction interface significantly affects the electron/hole processes in organic solar cells, including charge transfer (CT), exciton dissociation (ED), and charge recombination (CR). Here, to investigate interface molecular configuration effects, the donor‐acceptor complexes with face‐on, edge‐on, and end‐on configurations were constructed as model systems for the p‐SIDT(FBTTh2)2/C60 heterojunction. The geometries, electronic structures, and excitation properties of monomers and the complexes with three configurations were studied based on density functional theory (DFT) and time‐dependent DFT calculations with optimally tuned range separation parameters and solid polarization effects. In terms of Marcus theory, the rate constants of ED and CR processes were analyzed. The results show that most of the excited states for p‐SIDT(FBTTh2)2 exhibit an intramolecular CT character, and the similarity of the excitation characters (CT and local excitation) and energies among three complexes with different configurations indicate that the electronic structure and excitation properties are insensitive to the interfacial molecular configurations. However, the rates of ED and CR processes heavily depend on it. These results underline the importance of controlling molecular configuration and then the morphology at the heterojunction interface in organic solar cells. [ABSTRACT FROM AUTHOR]

• Introducing Ag dopant into CH 3 NH 3 PbI 3 is endothermic. • High concentration of Ag dopant increases the band gap. • Ag dopant leads to the increase of hole and electron effective masses. • Ag dopant enhances the exciton binding energy. In order to improve power conversion efficiency and stability, doping is commonly adopted strategy to tune and modify the structures and properties of CH 3 NH 3 PbI 3 materials in organic-inorganic hybrid perovskite emerging solar cells. Here, to understand the photovoltaic performance of Ag-doped perovskite CH 3 NH 3 PbI 3 at high dopant concentration, based upon density functional theory calculations for crystal structures, dopant formation energies, energy bands, density of states, optical absorptions, effective masses and exciton binding energies, we studied the effects of Pb replacement by Ag on electronic structures, optical and charge transport properties of perovskite CH 3 NH 3 PbI 3 with cubic, tetragonal and orthorhombic phases at Ag concentration of 12.5%. It was found that, introducing Ag dopant induces more significant distortion of AgI 6 octahedral. Also, introducing Ag dopant is possible to change the order of phase stability, and to improve the optical absorption properties of tetragonal phase. Furthermore, the Ag dopant shifts Fermi level to deep energy and slightly increases band gap without introducing extra dopant states. Whereas, the increased electron/hole effective masses by introducing Ag-dopant at this dopant concentration lead to the reduced charge carrier mobilities and imbalanced charge transport properties, and also result into more difficult exciton dissociation. [ABSTRACT FROM AUTHOR]

• Fluorination of end groups, thiophene modification. • Increasing the number of central rings. • These modifications can decrease the H-L gap. • Fluorine substitution promotes charge transfer at the heterojunction interface. • Increasing the central ring number lowers CR and enhances ED efficiency. Modifying the skeleton, side chains and end groups of non-fullerene acceptors (NFAs) is important approach to improve the photovoltaic performance of organic solar cells. We selected PBDB-T as the donor and INIC, INIC1, INIC2, ITCC, ITCPTC and ITIC as the acceptors in order to study the difference in NFAs. The geometries, electronic structures, excited state properties, excited-state lifetimes and rate constants of charge transfer (CT), charge recombination (CR) and exciton dissociation (ED) processes of the monomers and PBDB-T:NFA complexes have been investigated by means of density functional theory and time-dependent density functional theory. The research reveals that fluorination of end groups, thienyl substitution and increase in the number of central rings result in the decrease in the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Fluorine substitution and increase in central ring numbers cause redshift of the absorption spectrum for NFAs. NFAs with fluorine substitution have a larger maximum electrostatic potential, which facilitates CT at the donor:NFA heterojunction interfaces. Fluorine substitution and thienyl substitution decrease the NFA's CT distances, indicating that both fluorine and thienyl substitutions affect the CT rate. Fluorine substitution, thienyl modification of end groups and increase in central ring numbers also reduce the exciton binding energy, which is beneficial for decreasing CR and improving ED efficiency. [ABSTRACT FROM AUTHOR]

Abstract Development of novel dye sensitizers with suitable optoelectronic properties is effective to improve the power conversion efficiency of dye-sensitized solar cells (DSSCs). Considering the effectiveness of conjugate bridges in modification of optoelectronic properties, based on the dye sensitizers C201, C203, C204 and C205, five kinds of organic dye sensitizers are designed with different thiophene-based moieties and the functionalized graphene flakes (GFs) as conjugate bridges. The performances of these dye sensitizers are analyzed in terms of the calculated geometries, electronic structures and excitation properties. The transition configurations and molecular orbitals of dye sensitizers suggest that bis-dimethylfluoreneaniline is effective electron donor, and the transitions of optical absorption in visible region are charge transfer excitations. The conjugate lengths, energy level alignments, light harvesting capabilities, excitation character, and transition properties, as well as the free energy variations for electron injection and dye regeneration support that the designed dye sensitizers are effective to be applied in DSSCs. Particularly, introducing the functionalized GF into conjugate bridges significantly elongate conjugate length, reduce orbital energy gap, lead to denser distribution of orbital energy, generate red-shift of absorption spectra, enhance light harvesting capability, increase absorption bands and coefficients. Therefore, introducing the functionalized GF into conjugate bridges is effective, and the designed panchromatic dye sensitizer C20x-GF-BTD must be better than other designed dye sensitizers for DSSCs. Graphical abstract Image 1 Highlights • The electronic structures and properties of C201, C203, C204, C205 are calculated. • Five kinds of organic dye sensitizers are designed. • The effectiveness of the dye sensitizers in solar cells is analyzed. • The designed C20x-GF-BTD with the functionalized graphene flake must be better. [ABSTRACT FROM AUTHOR]

Abstract Understanding electronic structures and excitation properties is a fundamental issue to develop novel electron donor (D) and acceptor (A) molecular dyad that can be applied in optoelectronic systems. Here, the geometry, electronic structures, and excitation properties of three meso-pentafluorophenyl substituted zinc porphyrin fullerene ((F 15 P)ZnP C 60) dyad were analyzed based on density functional theory (DFT) and time dependent DFT (TDDFT) calculations. The geometrical parameters provide the D-A distance is about 18.19 Å. The electronic structure analysis indicates that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized in porphyrin core and C 60 , respectively. The transition configurations and the MOs suggest the excited states at the absorption maxima are local excited states, while the charge transfer (CT) states are transient intermediates. The population analysis supports the first singlet/triplet excited states are local excitations in porphyrin (LEP). Quasi-degeneracy of excited states between LEP and local excitation in C 60 (LEC) enable the partial delocalization of eigenstates and excitation-energies over the D and A in dyad, while the quasi-degeneracy between CT and LEP generate synergistic enhancement effects for CT. The results of this work could be helpful to understand optoelectronic properties of (F 15 P)ZnP C 60 dyad. Graphical abstract Image 1 Highlights • The electronic structure of (F 15 P)ZnP C 60 dyad is analyzed. • The transition configurations and the MOs of (F 15 P)ZnP C 60 dyad are calculated. • The population of (F 15 P)ZnP C 60 dyad are studied. • Quasi-degeneracy of excited states between LEP and local excitation in C 60 (LEC), and between CT and LEP are discussed. [ABSTRACT FROM AUTHOR]

As electronic acceptor materials in heterojunction, fullerene derivatives (FDs) can significantly affect the power conversion efficiency of organic solar cells (OSCs). Here, in order to investigate the number and size effects of fullerene-cage in FDs for OSCs, the geometries, electronic structures and related properties, as well as photovoltaic parameters of several FDs, including MP, PCBM, BP, TP and PC 71 BM, were analyzed based upon density functional theory (DFT) and time dependent DFT calculations. The results indicate that the fullerene-size is more important than the number of fullerene-unit to affect the local geometrical parameters, energy level alignments, hyper-polarizabilities, and optical absorptions in visible region. Furthermore, the lowest unoccupied molecular orbital (LUMO) energies are almost same for these FDs, and the orbital energies near frontier molecular orbitals for BP and TP exhibit two- and three-fold quasi-degenerate, respectively. The transition configurations and molecular orbitals reveal the absorption bands in visible region of MP, PCBM, PC 71 BM and TP are local excitations, and that of BP are charge transfer excitations. The similar open-circuit voltages and fill factors of OSCs based upon P3HT/MP, P3HT/PCBM, P3HT/BP, P3HT/TP, and P3HT/PC 71 BM blend films result from the similar LUMO energy levels of these FDs. [ABSTRACT FROM AUTHOR]

The design and development of novel dye sensitizers are effective method to improve the performance of dye-sensitized solar cells (DSSCs) because dye sensitizers have significant influence on photo-to-current conversion efficiency. In the procedure of dye sensitizer design, it is very important to understand how to tune their electronic structures and related properties through the substitution of electronic donors, acceptors, and conjugated bridges in dye sensitizers. Here, the electronic structures and excited-state properties of organic JK dye sensitizers are calculated by using density functional theory (DFT) and time dependent DFT methods. Based upon the calculated results, we investigated the role of different electronic donors, acceptors, and π-conjugated bridges in the modification of electronic structures, absorption properties, as well as the free energy variations for electron injection and dye regeneration. In terms of the analysis of transition configurations and molecular orbitals, the effective chromophores which are favorable for electron injection in DSSCs are addressed. Meanwhile, considering the absorption spectra and free energy variation, the promising electronic donors, π-conjugated bridges, and acceptors are presented to design dye sensitizers. [ABSTRACT FROM AUTHOR]

Abstract: The photon to current conversion efficiency of dye-sensitized solar cells (DSCs) can be significantly affected by dye sensitizers. The design of novel dye sensitizers with good performance in DSCs depend on the dye''s information about electronic structures and optical properties. Here, the geometries, electronic structures, as well as the dipole moments and polarizabilities of organic dye sensitizers C343 and 20 kinds of NKX derivatives were calculated using density functional theory (DFT), and the computations of the time dependent DFT with different functionals were performed to explore the electronic absorption properties. Based upon the calculated results and the reported experimental work, we analyzed the role of different conjugate bridges, chromophores, and electron acceptor groups in tuning the geometries, electronic structures, optical properties of dye sensitizers, and the effects on the parameters of DSCs were also investigated. [Copyright &y& Elsevier]

Abstract: The geometry, electronic structure, polarizability and hyperpolarizability of organic dye sensitizer TA-St-CA, which contains a π-conjugated oligo-phenylenevinylene unit with an electron donor–acceptor moiety, was studied using density functional theory (DFT), and the electronic absorption spectrum was investigated via time-dependent DFT (TD-DFT) with several hybrid functionals. The calculated geometry indicates that the strong conjugated effects are formed in the dye. The TD-DFT results show that the hybrid functional PBE1PBE and MPW1PW91 are more suitable than B3LYP for calculating electronic absorption spectra. The features of electronic absorption spectra were assigned on account of the qualitative agreement between the experiment and the calculations. The absorption bands in visible and near-UV region are related to photoinduced electron transfer processes, and the diphenylaniline group is major chromophore that contributed to the sensitization, and the interfacial electron transfer are electron injection processes from the excited dyes to the semiconductor conduction band. Compared with the similar dye D5, the good performance of TA-St-CA in dye-sensitized solar cells may be resulted from the higher energy level of the lowest unoccupied molecular orbital and the larger oscillator strengths for the most excited states with intramolecular electron transfer character. [Copyright &y& Elsevier]

[Display omitted] • Rb-doped double perovskites meet the requirements of perovskite structural stability. • Introducing Rb dopant into double perovskite Cs 2 AgBiBr 6 is exothermic. • Rb dopant cause direct band gap, and there are no the impurity states in band gap. • Rb dopant enhances the light absorption in the visible and infrared regions. • Rb dopant causes an increase (decrease) in the carrier mobility of electron (hole) Based upon supercell models and electronic structure calculations, we studied the effects of Rb-dopant for substituting Ag and Cs in double perovskite Cs 2 AgBiBr 6. The tolerance factors and octahedral factors suggest Rb-doped systems are stable. The dopant formation energies (-5.37 and −3.00 eV for subsituting Ag and Cs, respectively) indicate introducing Rb-dopant are exothermic. Rb-dopant changes the indirect band gap (2.25 eV) of pristine Cs 2 AgBiBr 6 into direct band gap (2.27 and 2.19 eV for subsituting Ag and Cs, respectively) without introducing impurity states in band gap. It also amplifies optical absorptions, decreases (increases) electron (hole) effective masses, and enlarges elastic constant. [ABSTRACT FROM AUTHOR]

The commonly existed vacancy defects in semiconductors can affect optoelectronic properties. Here, to understand the vacancy defect influences on double perovskite Cs 2 AgBiBr 6 , based upon density functional theory calculations and supercell model, we systematically investigated Cs, Ag, Bi, Br, Cs–Br and Ag–Br atomic pair vacancy effects on crystal structure, electronic structures, optical absorption, charge carrier and exciton binding energies. It was found that, the vacancy defects in double perovskite Cs 2 AgBiBr 6 induce slight deformation of crystal lattice. The vacancy defects cannot introduce extra defect states in the gap of energy band. The Cs, Ag, Bi, Ag–Br and Cs–Br defects not only change the band gap into the direct from the indirect of pristine system and reduce the band gap, but also promote the optical absorption capability, and result in red-shift of absorption spectra in low energy region. The Br vacancy leads to a heavy dopant character due to significant elevation of the Fermi level. The Cs, Ag, Bi, Ag–Br and Cs–Br vacancy defects also generate imbalanced charge transport properties, and increase exciton binding energies. • Vacancy defects cause small deformations of the crystal lattice. • No defect state is found in the band gap after introducing vacancy defects. • Vacancy defects promote light absorption and generate a red-shift. • Vacancy defects can cause unbalanced charge transport properties. [ABSTRACT FROM AUTHOR]