Molecular Orbital-Based Verification of Conductivity of Tetramethylammonium Pentaiodide and Pentaiodide-Based Electrolytes in Dye-Sensitized Solar Cells

Abstract

In order to verify the electrical conductivity of tetramethylammonium pentaiodide (TAPI, I 5 − (N(CH 3 ) 4 + )) crystal, molecular orbital configurations and energy structures of the electron-carrying state TAPI packing unit (TAPI-6) are examined by density functional theory (DFT). The narrow energy gap of the electron-carrying state radical anion of .− proves the semi-conductivity of TAPI together with the aligned configuration of singly occupied molecular orbital (SOMO) and the spin density distribution on SOMO. The molecular orbital analysis of the electron-accepted states of the vertical fragment unit of .− and the coplanar fragment unit of .− rationalize the anisotropic semiconducting property in TAPI. DFT-based molecular modeling for molecular integration of + I 3 − ] n . Additionally, the conductivity of TAPI is higher (about seven times) at the direction perpendicular to the coplanar aligned I 5 − components than at the direction parallel to the I 5 − -components. 1 A recent X-ray crystallography analysis of TAPI provided the precise structure of the TAPI crystal, and the packing unit structure, [N(CH 3 ) 4 + I 5 − ] 6 (TAPI-6) becomes available for DFT-based molecular orbital modeling.2 Molecular orbital (MO) structures of TAPI-6, the vertical fragment of (N(CH 3 ) 4 + I 5 − ) 4 (TAPI-4) and the coplanar fragment of (N(CH 3 ) 4 + I 5 − ) 3 (TAPI-3) in TAPI-6, are obtained by DFT-based single point calculations and examined in view of MO configuration and energy levels for interpretation of the anisotropic conductivity of TAPI (Fig. 1).With regard to the MO verification of electrical conductivity, band conduction, 3 hopping conduction, 4 and polaron conduction models were proposed. 5,6 The high charge mobility of organic semiconductor crystals was discussed using the hoping or the band model.7 By using the semi-classical dynamics and parameters obtained with the density functional theory (DFT) MO calculation of a single molecule or a molecular dimer, the hopping or the polaron model successfully described the high hole mobility of the organic semiconductors at room temperature. [8][9][10] One of the authors investigated the highest mobility of crystalline rubrene in view of the band dispersion, 11 and the electronic properties of methylammonium lead iodide perovskite [CH 3 NH 3 + PbI 3 − ] were discussed on the basis of effective masses of electrons and holes in the ambipolar transport. 12 As for the present MO-based verification of electrical conductivity, we took into consideration that the conductivity is observable under bias conditions and become dominant at electron-accepted states. Then, the molecular integrated systems that are interacting one another via van z

Computational Verification of So-Called Perovskite Solar Cells as PbI64−-Aligned Solar Cells

“…Energy structure analysis for verification of semiconducting property of the MeNH 3 PbI 3 -aligned layer in so-called PSC.-As we reported 6 in the previous theoretical study of electron mobility of tetramethylammonium pentaiodide and pentaiodide-based electrolytes in dye-sensitized solar cells, DFT-based single point calculations on the whole packing unit of the pale yellow PbI 6 4− crystal (FOLLIB) are carried out. The 3D molecular structures of FOLLIB (space filling model with C60 model, electrostatic potential map in unit of kJ/mol, the VASP-optimized crystal structure, and Mulliken charge on ball and wire structure) are shown in Fig.…”

“…All the 3D models show that the packing unit of FOLLIB is fully occupied by large 9 lead hexaiodide (PbI 6 4− ), one of which forms a central core unit with symmetrical three types of MeNH Figure S1, Tables S1). The Mulliken charge and the electrostatic potential map visualize molecular orbital-based van der Waals and coulomb interactions (vdW&Clb) in the pale yellow PbI 6 4− salt with MeNH 3…”

“…We investigate theoretical models of PbI 6 4− -aligned components by evaluating possible equilibrium states based on total energies (E), z E-mail: yanagida@mls.eng.osaka-u.ac.jp heats of formation ( E), electron energy structures and configurations of HOMO and LUMO, HOMO-LUMO energy gap, UV/Vis spectra, dipole moment and electronic charge of the components. To visualize their van der Waals and coulomb interactions, electron density structure, Mulliken charge, and electrostatic potential map are examined.…”

“…1 Since then, the name "perovskite solar cell (PSC)" has been introduced to most photovoltaic research and developments using methylammonium lead trihalides [MeNH 3 PbX 3 , (X = I, Br, and Cl)] as sensitizing chemicals. 2 On the other hand, it was reported in 1987 that drop-wise addition of a concentrated aqueous solution of Pb(NO 3 ) 2 to an aqueous solution containing excess MeNH 3 + I − yields a black precipitate of MeNH 3 PbI 3 , and that the solutions of MeNH 3 PbI 3 gives pale yellow crystalline solid that is composed of lead hexaiodide (PbI 6 4− ), MeNH 3 + and H 2 O. 3 In addition, the crystalline structure was analyzed by X-ray crystallography and the packing unit of the crystal is now coded as FOLLIB in Cambridge Structural Data (CSD).…”

“…3 In addition, the crystalline structure was analyzed by X-ray crystallography and the packing unit of the crystal is now coded as FOLLIB in Cambridge Structural Data (CSD). We understand that lead hexaiodide ion (PbI 6 4− ) are coordinated with methylammonium ion (MeNH 3 + ), changed into dark colored components in polar solvent, and predict that PbI 6 4− should play an essential role in efficient and effective molecular-structuring in perovskite-type solar cells, e.g., nanocrytalline TiO 2 (nc-TiO 2 )/MeNH 3 PbI 3 /spiro-OMeTAD-based PSC. Our density-functional-theory-based molecular modeling (DFT/MM) verifies essential roles of molecular alignment of PbI 6 4− components in electronic and photonic properties, i.e., high electron diffusion and diffusion length 4 and panchromatic light harvesting characteristics toward so-called PSC, i.e., PbI 6 4− -aligned solar cells.…”