New paradigm in molecular engineering of sensitizers for solar cell applications.

A novel thiocyanate-free cyclometalleted ruthenium sensitizer for solar cells is designed and developed. Upon anchoring to nanocrystalline TiO(2) films, it exhibits a remarkable incident monochromatic photon-to-current conversion efficiency of 83%. The solar cell employing a liquid-based electrolyte exhibits a short circuit photocurrent density of 17 mA/cm(2), an open circuit voltage of 800 mV, and a fill factor of 0.74, corresponding to an overall conversion efficiency of 10.1% at standard AM 1.5 sunlight. To understand the structural, electronic, and optical properties of the cyclometalleted ruthenium sensitizer, we have investigated using density functional theory (DFT) and time-dependent DFT (TDDFT). Our results show the HOMO is located mostly on ruthenium and cyclometalated ligand, while the LUMO is on 4-carboxylic acid-4'-carboxylate-2,2'-bipyridine. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, and TDDFT calculations allowed assignment of the visible absorption bands. The present findings provide new design criteria for the next generation of ruthenium sensitizers and help foster widespread interest in the engineering of new sensitizers that interact effectively with the I(-)/I(3)(-) redox couple.

[1]  P. Liska,et al.  Acid-Base Equilibria of (2,2'-Bipyridyl-4,4'-dicarboxylic acid)ruthenium(II) Complexes and the Effect of Protonation on Charge-Transfer Sensitization of Nanocrystalline Titania. , 1999, Inorganic chemistry.

[2]  Hidetoshi Miura,et al.  High efficiency of dye-sensitized solar cells based on metal-free indoline dyes. , 2004, Journal of the American Chemical Society.

[3]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[4]  Peng Wang,et al.  A stable quasi-solid-state dye-sensitized solar cell with an amphiphilic ruthenium sensitizer and polymer gel electrolyte , 2003, Nature materials.

[5]  H. Stoll,et al.  Energy-adjustedab initio pseudopotentials for the second and third row transition elements , 1990 .

[6]  K. Wijayantha,et al.  Electron transport and back reaction in dye sensitised nanocrystalline photovoltaic cells , 2000 .

[7]  Filipp Furche,et al.  Adiabatic time-dependent density functional methods for excited state properties , 2002 .

[8]  Dmitrij Rappoport,et al.  Density functional methods for excited states: equilibrium structure and electronic spectra , 2005 .

[9]  W. Warta,et al.  Solar cell efficiency tables (version 33) , 2009 .

[10]  Qing Wang,et al.  DFT-INDO/S modeling of new high molar extinction coefficient charge-transfer sensitizers for solar cell applications. , 2006, Inorganic chemistry.

[11]  R. Ahlrichs,et al.  Treatment of electronic excitations within the adiabatic approximation of time dependent density functional theory , 1996 .

[12]  A. J. Frank,et al.  Morphological and photoelectrochemical characterization of core-shell nanoparticle films for dye-sensitized solar cells: Zn-O type shell on SnO2 and TiO2 cores. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[13]  Y. Tachibana,et al.  Dye-Sensitized Nanocrystalline TiO2 Solar Cells Based on Ruthenium(II) Phenanthroline Complex Photosensitizers , 2001 .

[14]  Anders Hagfeldt,et al.  A New Method for Manufacturing Nanostructured Electrodes on Plastic Substrates , 2001 .

[15]  P. Liska,et al.  Engineering of efficient panchromatic sensitizers for nanocrystalline TiO(2)-based solar cells. , 2001, Journal of the American Chemical Society.

[16]  M. Grätzel,et al.  A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films , 1991, Nature.

[17]  A. Spek,et al.  Cyclometalated ruthenium complexes for sensitizing nanocrystalline TiO2 solar cells. , 2007, Chemical communications.

[18]  F. Weigend,et al.  Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. , 2005, Physical chemistry chemical physics : PCCP.

[19]  Frank Nüesch,et al.  Co-sensitization of organic dyes for efficient ionic liquid electrolyte-based dye-sensitized solar cells. , 2007, Langmuir : the ACS journal of surfaces and colloids.

[20]  Juan Bisquert,et al.  Physical Chemical Principles of Photovoltaic Conversion with Nanoparticulate, Mesoporous Dye-Sensitized Solar Cells , 2004 .

[21]  Emilio Palomares,et al.  Supermolecular control of charge transfer in dye-sensitized nanocrystalline TiO2 films: towards a quantitative structure-function relationship. , 2005, Angewandte Chemie.

[22]  Seigo Ito,et al.  Photovoltaic characterization of dye‐sensitized solar cells: effect of device masking on conversion efficiency , 2006 .