Study on Charge Separation and Collection for stable mesoscopic sensitized solar cells Li Feng (Bachelor of Eng, SJTU) A thesis submitted for the degree of Doctor of Philosophy Department of Material Science and Engineering National University of Singapore 2013-08 ‐ 1 ‐    DECLARATION I hereby declare that this thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. …………………… Li Feng August, 2013 ‐ 2 ‐    ACKNOWLEDGEMENTS At first, I would like to express my deepest thanks and gratitude to my supervisor Dr. WANG QING for his advice and instruction with kindness and wisdom on research as well as on personality in the past four years. Second, my profound thanks must be extended to Dr. James Robert Jennings, as his enthusiasm in research greatly encouraged me. Moreover, thanks to the abundant discussions with and advices from him, my horizon has been broadened significantly, both theoretically and experimentally. Third, I’d like to thank Mr. Julianto Chua and his supervisor Prof. Subodh Mhaisalkar at NTU for their fruitful help in the fabrication of solid-state dye-sensitized solar cells. My heart-felt thanks also go to my friends, Ms. Liu Yeru, Ms. Fan Li, Dr. Sun Lidong, Dr. Md. Anower HOSSAIN, Dr. Xingzhu Wang, Ms. Koh Zhen Yu, Mr. Huang Qizhao, Mr. Shen Chao and Mr. Pan Feng, for their kind help on the study itself, as well as understanding and tolerance of my heavy equipment occupancy. Besides, I’d like to thank my friend Zhang Wei and his supervisor Professor Liu Bin, for the chance to work with their group on solid state dye-sensitized solar cells. Thanks for the scholarship and equipment offered by NUS and fundings (NUS startup grant No. R-284-000-064-133; URC grant No. R-284-000-068-112; NRF CRP grant No. R-284-000-079-592). Lastly, my forever gratitude goes to my parents, parents-in-law and wife for their great love, understanding and support. ‐ 3 ‐    Table of Contents DECLARATION   ‐ 2 ‐  ACKNOWLEDGEMENTS  . ‐ 3 ‐  Summary  . ‐ 7 ‐  List of Symbols and Abbreviations  ‐ 9 ‐  List of Figures and Tables  . ‐ 12 ‐  Chapter 1. Introduction   ‐ 14 ‐  1.1 Renewable Energy  . ‐ 14 ‐  1.2 Basic Concept and Working Principles of DSCs  . ‐ 16 ‐  1.3 Improving the Performance and Stability of DSCs   ‐ 20 ‐  Chapter 2. Models for Charge Transport and Transfer in DSCs   ‐ 23 ‐  2.1 j-V Characteristic, the Origin of Photovoltage and Photocurrent  . ‐ 23 ‐  2.1.1 Origin of Photovoltage  . ‐ 24 ‐  2.1.2 IPCE, Light Harvesting and Electron Injection   ‐ 25 ‐  2.2 Dye regeneration  . ‐ 28 ‐  2.3 Electron Transport and Recombination  . ‐ 30 ‐  2.3.1 Diffusion Model, trap free case   ‐ 32 ‐  2.3.2 Multiple Trapping Model  . ‐ 33 ‐  2.4 Mass transport.   ‐ 35 ‐  Chapter 3. Experiment Methods  . ‐ 37 ‐  3.1 Fabrication of DSCs with liquid electrolyte.  . ‐ 37 ‐  3.2 Characterization Methods  . ‐ 38 ‐  3.2.1 j-V characteristics  . ‐ 38 ‐  3.2.2 IPCE under different conditions.   ‐ 38 ‐  3.2.3 Impedance Spectroscopy.  . ‐ 39 ‐  3.2.4 Transient Absorption Spectroscopy  ‐ 42 ‐  3.2.5 Other Characterization Techniques.  . ‐ 44 ‐  ‐ 4 ‐    Chapter 4. Evolution of Charge Collection / Separation Efficiencies in Dye-sensitized Solar Cells upon Aging   ‐ 46 ‐  4.1 Introduction  . ‐ 46 ‐  4.2 Experiments  . ‐ 47 ‐  4.3 Results and Discussions   ‐ 48 ‐  4.3.1 j-V Characteristics.  . ‐ 48 ‐  4.3.2 Interpretation of Voc evolution  ‐ 50 ‐  4.3.3 Evolution of charge collection efficiency.  . ‐ 53 ‐  4.3.4 Evolution of separation efficiency derived from short-circuit IPCE.  . ‐ 55 ‐  4.3.5 Evolution of separation efficiency derived from OC IPCE.   ‐ 59 ‐  4.4 Conclusions  . ‐ 61 ‐  Chapter 5. Determining the Conductivities of the Two Charge Transport Phases in Solid-State Dye -Sensitized Solar Cells by Impedance Spectroscopy  . ‐ 63 ‐  5.1 Introduction  . ‐ 63 ‐  5.2 Experimental Section  . ‐ 66 ‐  5.2.1 Fabrication of ss-DSCs.  . ‐ 66 ‐  5.2.2 Device Characterization.   ‐ 67 ‐  5.3 Results and Discussion   ‐ 67 ‐  5.4 Conclusions  . ‐ 77 ‐  Chapter 6. Determination of Sensitizer Regeneration Efficiency in Dye-Sensitized Solar Cells ‐ 78 ‐  6.1 Introduction  . ‐ 78 ‐  6.2 Experiments and Methods  . ‐ 80 ‐  6.3 Results and Discussion   ‐ 81 ‐  6.3.1 Determination of regeneration efficiency using transient and steady-state approaches.   ‐ 81 ‐  6.3.2 Dependence of electron concentration on photon flux in regular and inert cells.   ‐ 89 ‐  6.3.3 Dependence of EDR rate constant on electron concentration in inert cells.   ‐ 91 ‐  6.3.4 Regeneration efficiency under working conditions.   ‐ 94 ‐  6.4 Conclusion . ‐ 95 ‐  Chapter 7. Influence of supporting electrolyte concentration on photocurrent of dye-sensitized solar cells employing robust electrolytes.  . ‐ 97 ‐  7.1 Introduction  . ‐ 97 ‐  ‐ 5 ‐    7.2 Experiments  . ‐ 98 ‐  7.3 Results and discussion  . ‐ 99 ‐  7.3.1 j-V Characteristics   ‐ 99 ‐  7.3.2 Mono IPCE and OC IPCE   ‐ 100 ‐  7.3.3 Light harvesting efficiency and charge collection efficiency  . ‐ 101 ‐  7.3.4 Charge separation efficiency   ‐ 103 ‐  7.4 Conclusion  . ‐ 106 ‐  Conclusions and Outlook   ‐ 107 ‐  Appendix  . ‐ 111 ‐  A.1. Derivation of the impedance expression.  . ‐ 111 ‐  A.2. Redundancy Examination.  . ‐ 112 ‐  A.3. Effect of “parallel” overlayer.  . ‐ 114 ‐  A.4. Typical simulations of electron channel.  . ‐ 115 ‐  References  . ‐ 116 ‐  Publications  . ‐ 130 ‐  ‐ 6 ‐    Summary Current-voltage (j-V) characteristics, impedance spectroscopy (IS) and incident photon to current efficiency (IPCE) were monitored for dye-sensitized solar cells (DSCs) employing different electrolytes under a range of different conditions over one month, in order to correlate the evolution of short-circuit current density , open-circuit voltage and power conversion efficiency (PCE) to the energetic and kinetic parameters such as TiO2 conduction band edge ( ) and effective dye regeneration rate constant. Although no standard aging protocol was followed in this study, the ‘pseudo-aging’ test represents the first attempt to de-convolute various kinetic processes upon prolonged aging, and has provided new insights into device operation. To apply IS for studying charge transport in the mesoporous film of solid-state dye-sensitized solar cells (ss-DSCs), it is necessary to determine the relative conductivities of the electron and hole transporting phases, given the equivalent positions of the distributed electron and hole transport resistances ( and ) in the equivalent circuit. Here in-plane transistor-like ss-DSCs employing spiro-OMeTAD as hole conductor were fabricated and characterized with IS. By design, and are no longer in equivalent positions as they were in ss-DSCs with regular solar cell geometry (regular ss-DSCs), providing a means to determine their values independently. Fitting and simulation results of transistor-like devices combined with cross checks against results obtained for regular ss-DSCs clearly showed that significantly larger than is under all conditions studied. Charge transport and transfer in ss-DSCs were then discussed and effective carrier diffusion lengths are calculated. The results suggested that charge collection is limited by an inadequate electron diffusion length ( ) in ss-DSCs, implying the necessity to enhance electron transport or retard recombination in order to improve the performance of ss-DSCs. The experimental methodology proposed here will find important use in other ss-DSCs. Regeneration of the oxidized dye in DSCs is frequently studied using the transient absorption (TA) technique. However, TA measurements are generally not performed using ‐ 7 ‐    complete DSCs at the maximum power point (MPP) on the j-V curve, and the electron concentration in the nanocrystalline TiO2 films used in these devices is often not well characterized, which may lead to results that are not relevant to actual solar cell operation. In this work, dye regeneration kinetics was studied at the MPP and at open circuit (where interpretation of results is simpler). Using a combination of TA, differential IPCE measurements and IS, the dependence of electron-dye recombination rate and overall sensitizer regeneration efficiency on TiO2 electron concentration was unambiguously demonstrated. The validity of a commonly used approach for determining regeneration efficiency in which the electron-dye recombination rate constant is estimated from TA decays of cells employing a redox-inactive electrolyte solution was also examined. It was found that this widespread practice may be unsuitable for accurate determination of the regeneration rate constant or efficiency. It was further shown that, despite near-quantitative regeneration at short circuit or low photovoltage, PCE was limited by inefficient regeneration in stable DSCs with practically relevant electrolyte solutions using I /I as redox mediator. The effect of a systematic variation of supporting electrolyte (SE) concentration on photocurrent of DSCs using low-volatility electrolytes, which showed good long-term stability and usually possess high viscosity and ionic strength, was examined. A degradation of the j-V characteristics and PCE with increasing SE concentration was observed. The relative importance of electrolyte viscosity and ionic strength in determining charge collection and charge separation yields were discussed. After correction of charge collection losses, it was found that even near open-circuit conditions where mass transport effects can be neglected, charge separation yield is strongly dependent on SE concentration, which was qualitatively consistent with a kinetic electrolyte effect or possibly ionic strength/viscosity related modulation in reorganization energies. The results implied the importance of voltage-dependent dye regeneration yield for solvent-free electrolytes, where ionic strength and viscosity are usually very high. ‐ 8 ‐    List of Symbols and Abbreviations cross section area of the mesoporous film chemical capacitance of the mesoporous film distributed (normalized) chemical capacitance of the mesoporous film thickness of the mesoporous film free electron diffusion coefficient without trapping and detrapping D oxidized dye molecule effective electron diffusion coefficient with trapping and detrapping DSCs Dye-sensitized Solar Cells TiO2 conduction band edge EDR Electron Dye Recombination EER Electron Electrolyte Recombination , quasi Fermi level of electrons in TiO2 , Fermi level of redox couples in the electrolyte frequency FF Fill Factor FTO Fluorine doped Tin-Oxide HOMO highest occupied molecular orbital HTM Hole Transporting Material incident photon flux IL Ionic Liquid IPCE Incident Photon to Current Efficiency IS Impedance Spectroscopy ‐ 9 ‐    j-V current-voltage characteristics short-circuit current density Boltzman constant EDR rate constant EER rate constant pseudo first-order EER rate constant dye regeneration rate constant pseudo first-order dye regeneration rate constant free electron diffusion length effective electron diffusion length effective hole diffusion length LUMO lowest unoccupied molecular orbital MPP Maximum Power Point free electron concentration in the mesoporous film trapped electron concentration in the mesoporous film total electron concentration in the mesoporous film PCE Power Conversion Efficiency PD photo-diode elementary charge QFL Quasi Fermi Level constant phase element (non-ideal chemical capacitance) distributed (normalized) constant phase element charge transfer (recombination) resistance of the mesoporous film distributed (normalized) charge transfer (recombination) resistance ‐ 10 ‐    References References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. Bp Statistical Review of World Energy. 2012. Renewables 2013 Global Status Report. Renewable Energy Policy Network for the 21st Century, 2013. International Energy Statistics. Energy Information Adminastration,U.S., 2013. Solar Energy. WIKIPEDIA, 2013. Faunce, T., et al., Artificial Photosynthesis as a Frontier Technology for Energy Sustainability. Energy & Environmental Science, 2013. 6(4): p. 1074-1076. Photovoltaics Report. FRAUNHOFER INSTITUTE FOR SOLAR ENERGY SYSTEMS ISE, 2012. Grätzel, M., Photoelectrochemical Cells. Nature, 2001. 414(6861): p. 338-344. O'regan, B. and M. Grätzel, A Low-Cost, High-Efficiency Solar-Cell Based on Dye-Sensitized Colloidal TiO2 Films. Nature, 1991. 353(6346): p. 737-740. Grätzel, M., Recent Advances in Sensitized Mesoscopic Solar Cells. Accounts of Chemical Research, 2009. 42(11): p. 1788-1798. Hagfeldt, A., et al., Dye-Sensitized Solar Cells. Chemical Reviews, 2010. 110(11): p. 6595-6663. Kroon, J.M., et al., Nanocrystalline Dye-Sensitized Solar Cells Having Maximum Performance. Progress in Photovoltaics: Research and Applications, 2007. 15(1): p. 1-18. Gregg, B.A., Excitonic Solar Cells. The Journal of Physical Chemistry B, 2003. 107(20): p. 4688-4698. Grätzel, M., Sol-Gel Processed TiO2 Films for Photovoltaic Applications. Journal of Sol-Gel Science and Technology, 2001. 22(1-2): p. 7-13. Galoppini, E., et al., Fast Electron Transport in Metal Organic Vapor Deposition Grown Dye-Sensitized ZnO Nanorod Solar Cells. The Journal of Physical Chemistry B, 2006. 110(33): p. 16159-16161. Shankar, K., et al., Highly Efficient Solar Cells Using TiO2 Nanotube Arrays Sensitized with a Donor-Antenna Dye. Nano Letters, 2008. 8(6): p. 1654-1659. Ghicov, A. and P. Schmuki, Self-Ordering Electrochemistry: A Review on Growth and Functionality of TiO2 Nanotubes and Other Self-Aligned Mox Structures. Chemical Communications, 2009(20): p. 2791-2808. Gonzalez-Valls, I. and M. Lira-Cantu, Vertically-Aligned Nanostructures of ZnO for Excitonic Solar Cells: A Review. Energy & Environmental Science, 2009. 2(1): p. 19-34. Qin, P., et al., High Incident Photon-to-Current Conversion Efficiency of P-Type Dye-Sensitized Solar Cells Based on NiO and Organic Chromophores. Advanced Materials, 2009. 21(29): p. 2993-2996. ‐ 116 ‐    References 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. Yu, M., et al., P-Type Dye-Sensitized Solar Cells Based on Delafossite CuGaO2 Nanoplates with Saturation Photovoltages Exceeding 460 mV. The Journal of Physical Chemistry Letters, 2012. 3(9): p. 1074-1078. Nazeeruddin, M.K. and M. Grätzel, Transition Metal Complexes for Photovoltaic and Light Emitting Applications, in Photofunctional Transition Metals Complexes. 2007. p. 113-175. Nazeeruddin, M.K., et al., Stepwise Assembly of Amphiphilic Ruthenium Sensitizers and Their Applications in Dye-Sensitized Solar Cell. Coordination Chemistry Reviews, 2004. 248(13-14): p. 1317-1328. Mishra, A., M.K.R. Fischer, and P. Bäuerle, Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules. Angewandte Chemie International Edition, 2009. 48(14): p. 2474-2499. Choi, H., et al., Highly Efficient and Thermally Stable Organic Sensitizers for Solvent-Free Dye-Sensitized Solar Cells. Angewandte Chemie, 2008. 120(2): p. 333-336. Shen, Q., et al., Effect of ZnS Coating on the Photovoltaic Properties of CdSe Quantum Dot-Sensitized Solar Cells. Journal of Applied Physics, 2008. 103(8). Hossain, M.A., et al., Mesoporous SnO2 Spheres Synthesized by Electrochemical Anodization and Their Application in Cdse-Sensitized Solar Cells. The Journal of Physical Chemistry C, 2010. 114(49): p. 21878-21884. Balasingam, S.K., et al., Improvement of Dye-Sensitized Solar Cells toward the Broader Light Harvesting of the Solar Spectrum. Chemical Communications, 2013. 49(15): p. 1471-1487. Kim, H.S., et al., Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci Rep, 2012. 2: p. 591. Chung, I., et al., All-Solid-State Dye-Sensitized Solar Cells with High Efficiency. Nature, 2012. 485(7399): p. 486-489. Lee, M.M., et al., Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science, 2012. 338(6107): p. 643-647. Ball, J.M., et al., Low-Temperature Processed Meso-Superstructured to Thin-Film Perovskite Solar Cells. Energy & Environmental Science, 2013. 6(6): p. 1739-1743. Burschka, J., et al., Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells. Nature, 2013. 499(7458): p. 316-319. Kim, H.-S., et al., Mechanism of Carrier Accumulation in Perovskite Thin-Absorber Solar Cells. Nat Commun, 2013. 4. Gonzalez-Pedro, V., et al., General Working Principles of CH3NH3PbX3 Perovskite Solar Cells. Nano Letters, 2014. Zhao, Y., A.M. Nardes, and K. Zhu, Solid-State Mesostructured Perovskite CH3NH3PbI3 Solar Cells: Charge Transport, Recombination, and Diffusion Length. The Journal of Physical Chemistry Letters, 2014: p. 490-494. ‐ 117 ‐    References 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. Daeneke, T., et al., High-Efficiency Dye-Sensitized Solar Cells with Ferrocene-Based Electrolytes. Nat Chem, 2011. 3(3): p. 211-215. Spiccia, L., Dye Regeneration and Charge Recombination in Dye-Sensitized Solar Cells with Ferrocene Derivatives as Redox Mediators. Energy & Environmental Science, 2012. 5: p. 7090-7099. Zhou, D., et al., Efficient Organic Dye-Sensitized Thin-Film Solar Cells Based on the tris(1,10-phenanthroline)Cobalt(II/III) Redox Shuttle. Energy & Environmental Science, 2011. 4(6): p. 2030-2034. Liu, Y., et al., Significant Performance Improvement in Dye-Sensitized Solar Cells Employing the Cobalt(III/II) Tris-bipyridyl Redox Mediator by Co-Grafting Alkyl Phosphonic Acids with a Ruthenium Sensitizer. Physical Chemistry Chemical Physics, 2013. Kashif, M.K., et al., Stable Dye-Sensitized Solar Cell Electrolytes Based on Cobalt(II)/(III) Complexes of a Hexadentate Pyridyl Ligand. Angewandte Chemie International Edition, 2013. 52(21): p. 5527-5531. Feldt, S.M., et al., Regeneration and Recombination Kinetics in Cobalt Polypyridine Based Dye-Sensitized Solar Cells, Explained Using Marcus Theory. Physical Chemistry Chemical Physics, 2013. Feldt, S.M., et al., Effects of Driving Forces for Recombination and Regeneration on the Photovoltaic Performance of Dye-Sensitized Solar Cells Using Cobalt Polypyridine Redox Couples. The Journal of Physical Chemistry C, 2011. 115(43): p. 21500-21507. Zakeeruddin, S.M. and M. Grätzel, Solvent-Free Ionic Liquid Electrolytes for Mesoscopic Dye-Sensitized Solar Cells. Advanced Functional Materials, 2009. 19(14): p. 2187-2202. Shi, D., et al., New Efficiency Records for Stable Dye-Sensitized Solar Cells with Low-Volatility and Ionic Liquid Electrolytes. The Journal of Physical Chemistry C, 2008. 112(44): p. 17046-17050. Spiccia, L., Aqueous Dye-Sensitized Solar Cell Electrolytes Based on the Cobalt(II)/(III) Tris(Bipyridine) Redox Couple. Energy & Environmental Science, 2012. Daeneke, T., et al., Aqueous Dye-Sensitized Solar Cell Electrolytes Based on the Ferricyanide–Ferrocyanide Redox Couple. Advanced Materials, 2012. 24(9): p. 1222-1225. Muto, T., et al., Conductive Polymer-Based Mesoscopic Counterelectrodes for Plastic Dye-Sensitized Solar Cells. Chemistry Letters, 2007. 36(6): p. 804-805. Wu, M., et al., Low-Cost Dye-Sensitized Solar Cell Based on Nine Kinds of Carbon Counter Electrodes. Energy & Environmental Science, 2011. 4(6): p. 2308-2315. Wu, M. and T. Ma, Platinum-Free Catalysts as Counter Electrodes in Dye-Sensitized Solar Cells. ChemSusChem, 2012. 5(8): p. 1343-1357. ‐ 118 ‐    References 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. Grätzel, M., Conversion of Sunlight to Electric Power by Nanocrystalline Dye-Sensitized Solar Cells. Journal of Photochemistry and Photobiology a-Chemistry, 2004. 164(1-3): p. 3-14. Boschloo, G. and A. Hagfeldt, Characteristics of the Iodide/Triiodide Redox Mediator in Dye-Sensitized Solar Cells. Accounts of Chemical Research, 2009. Jennings, J.R., F. Li, and Q. Wang, Reliable Determination of Electron Diffusion Length and Charge Separation Efficiency in Dye-Sensitized Solar Cells. Journal of Physical Chemistry C, 2010. 114(34): p. 14665-14674. Hagfeldt, A. and M. Grätzel, Light-Induced Redox Reactions in Nanocrystalline Systems. Chemical Reviews, 1995. 95(1): p. 49-68. Wu, J., et al., An All-Solid-State Dye-Sensitized Solar Cell-Based Poly(N-Alkyl-4-Vinyl-Pyridine Iodide) Electrolyte with Efficiency of 5.64%. Journal of the American Chemical Society, 2008. 130(35): p. 11568-11569. Snaith, H.J., et al., Efficiency Enhancements in Solid-State Hybrid Solar Cells Via Reduced Charge Recombination and Increased Light Capture. Nano Letters, 2007. 7(11): p. 3372-3376. Yum, J.-H., et al., Recent Developments in Solid-State Dye-Sensitized Solar Cells. ChemSusChem, 2008. 1(8-9): p. 699-707. Zhang, W., et al., High-Performance Solid-State Organic Dye Sensitized Solar Cells with P3HT as Hole Transporter. The Journal of Physical Chemistry C, 2011. 115(14): p. 7038-7043. Kumara, G.R.A., et al., Dye-Sensitized Solid-State Solar Cells Made from Magnesiumoxide-Coated Nanocrystalline Titanium Dioxide Films: Enhancement of the Efficiency. Journal of Photochemistry and Photobiology A-Chemistry, 2004. 164(1-3): p. 183-185. Spiccia, L., U. Bach, and W. Xiang, Stable High Efficiency Dye-Sensitized Solar Cells Based on a Cobalt Polymer Gel Electrolyte. Chemical Communications, 2013. 49(79): p. 8997-8999. Halme, J., et al., Spectral Characteristics of Light Harvesting, Electron Injection, and Steady-State Charge Collection in Pressed TiO2 Dye Solar Cells. The Journal of Physical Chemistry C, 2008. 112(14): p. 5623-5637. Asbury, J.B., et al., Femtosecond Ir Study of Excited-State Relaxation and Electron-Injection Dynamics of Ru(dcbpy)2(NCS)2 in Solution and on Nanocrystalline TiO2 and Al2O3 Thin Films. The Journal of Physical Chemistry B, 1999. 103(16): p. 3110-3119. Ramakrishna, G., et al., Strongly Coupled Ruthenium-Polypyridyl Complexes for Efficient Electron Injection in Dye-Sensitized Semiconductor Nanoparticles. Journal of Physical Chemistry B, 2005. 109(32): p. 15445-15453. Kuang, D.B., et al., High Molar Extinction Coefficient Heteroleptic Ruthenium Complexes for Thin Film Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2006. 128(12): p. 4146-4154. ‐ 119 ‐    References 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. Benko, G., et al., Photoinduced Ultrafast Dye-to-Semiconductor Electron Injection from Nonthermalized and Thermalized Donor States. Journal of the American Chemical Society, 2002. 124(3): p. 489-493. Koops, S.E., et al., Parameters Influencing the Efficiency of Electron Injection in Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2009. 131(13): p. 4808-4818. Kelly, C.A., et al., Cation-Controlled Interfacial Charge Injection in Sensitized Nanocrystalline TiO2. Langmuir, 1999. 15(20): p. 7047-7054. Haque, S.A., et al., Charge Separation versus Recombination in Dye-Sensitized Nanocrystalline Solar Cells:  The Minimization of Kinetic Redundancy. Journal of the American Chemical Society, 2005. 127(10): p. 3456-3462. Tiwana, P., et al., Electron Mobility and Injection Dynamics in Mesoporous ZnO, SnO2, and TiO2 Films Used in Dye-Sensitized Solar Cells. ACS Nano, 2011. 5(6): p. 5158-5166. Koops, S.E. and J.R. Durrant, Transient Emission Studies of Electron Injection in Dye Sensitised Solar Cells. Inorganica Chimica Acta, 2008. 361(3): p. 663-670. Jennings, J.R. and Q. Wang, Influence of Lithium Ion Concentration on Electron Injection, Transport, and Recombination in Dye-Sensitized Solar Cells. Journal of Physical Chemistry C, 2010. 114(3): p. 1715-1724. Durrant, J.R., S.A. Haque, and E. Palomares, Photochemical Energy Conversion: From Molecular Dyads to Solar Cells. Chemical Communications, 2006. 0(31): p. 3279-3289. Ziółek, M., et al., Aggregation and Electrolyte Composition Effects on the Efficiency of Dye-Sensitized Solar Cells. A Case of a near-Infrared Absorbing Dye for Tandem Cells. The Journal of Physical Chemistry C, 2013. Buhbut, S., et al., Controlling Dye Aggregation, Injection Energetics and Catalytic Recombination in Organic Sensitizer Based Dye Cells Using a Single Electrolyte Additive. Energy & Environmental Science, 2013. Tachibana, Y., et al., Modulation of the Rate of Electron Injection in Dye-Sensitized Nanocrystalline TiO2 Films by Externally Applied Bias. Journal of Physical Chemistry B, 2001. 105(31): p. 7424-7431. Anderson, A.Y., et al., Quantifying Regeneration in Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 2011. 115(5): p. 2439-2447. Boschloo, G. and A. Hagfeldt, Characteristics of the Iodide/Triiodide Redox Mediator in Dye-Sensitized Solar Cells. Accounts of Chemical Research, 2009. 42(11): p. 1819-1826. Pelet, S., J.E. Moser, and M. Grätzel, Cooperative Effect of Adsorbed Cations and Iodide on the Interception of Back Electron Transfer in the Dye Sensitization of Nanocrystalline TiO2. Journal of Physical Chemistry B, 2000. 104(8): p. 1791-1795. Clifford, J.N., et al., Dye Dependent Regeneration Dynamics in Dye Sensitized Nanocrystalline Solar Cells:  Evidence for the Formation of a Ruthenium ‐ 120 ‐    References 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. Bipyridyl Cation/Iodide Intermediate. The Journal of Physical Chemistry C, 2007. 111(17): p. 6561-6567. Alebbi, M., et al., The Limiting Role of Iodide Oxidation in cis-os(dcb)(2)(CN)(2)/TiO2 Photoelectrochemical Cells. Journal of Physical Chemistry B, 1998. 102(39): p. 7577-7581. Martiniani, S., et al., New Insight into the Regeneration Kinetics of Organic Dye Sensitised Solar Cells. Chemical Communications, 2012. 48(18): p. 2406-2408. Cappel, U.B., et al., Dye Regeneration by Spiro- MeOTAD in Solid State Dye-Sensitized Solar Cells Studied by Photoinduced Absorption Spectroscopy and Spectroelectrochemistry. The Journal of Physical Chemistry C, 2009. 113(15): p. 6275-6281. Klahr, B.M. and T.W. Hamann, Performance Enhancement and Limitations of Cobalt Bipyridyl Redox Shuttles in Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 2009. 113(31): p. 14040-14045. O'Regan, B., et al., Vectorial Electron Injection into Transparent Semiconductor Membranes and Electric Field Effects on the Dynamics of Light-Induced Charge Separation. The Journal of Physical Chemistry, 1990. 94(24): p. 8720-8726. Nazeeruddin, M.K., et al., Conversion of Light to Electricity by cis-X2bis(2,2'-Bipyridyl-4,4'-Dicarboxylate)Ruthenium(II) Charge-Transfer Sensitizers (X = Cl-, Br-, I-, CN-, and SCN-) on Nanocrystalline TiO2 Electrodes. Journal of the American Chemical Society, 1993. 115(14): p. 6382-6390. Huang, S.Y., et al., Charge Recombination in Dye-Sensitized Nanocrystalline TiO2 Solar Cells. Journal of Physical Chemistry B, 1997. 101(14): p. 2576-2582. Haque, S.A., et al., Parameters Influencing Charge Recombination Kinetics in Dye-Sensitized Nanocrystalline Titanium Dioxide Films. Journal of Physical Chemistry B, 2000. 104(3): p. 538-547. Schlichthorl, G., N.G. Park, and A.J. Frank, Evaluation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO2 Solar Cells. Journal of Physical Chemistry B, 1999. 103(5): p. 782-791. Yella, A., et al., Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency. Science, 2011. 334(6056): p. 629-634. Li, X., et al., Efficient Dye-Sensitized Solar Cells with Potential-Tunable Organic Sulfide Mediators and Graphene-Modified Carbon Counter Electrodes. Advanced Functional Materials, 2013: p. n/a-n/a. Burschka, J., et al., Influence of the Counter Electrode on the Photovoltaic Performance of Dye-Sensitized Solar Cells Using a Disulfide/Thiolate Redox Electrolyte. Energy & Environmental Science, 2012. ‐ 121 ‐    References 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. Liu, Y., et al., An Organic Redox Mediator for Dye-Sensitized Solar Cells with near Unity Quantum Efficiency. Energy & Environmental Science, 2011. 4(2): p. 564-571. Daeneke, T., et al., Dye Regeneration Kinetics in Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2012. 134(41): p. 16925-16928. DAVID SHOUP, A.S., Role of Diffusion in Ligand Binding to Macromolecules and Cell-Bound Receptors. Biophysical Journal, 1982. 40: p. 33-39. Baxter, J.B. and E.S. Aydil, Nanowire-Based Dye-Sensitized Solar Cells. Applied Physics Letters, 2005. 86(5). Hyk, W. and J. Augustynski, Steady-State Operation of Porous Photoelectrochemical Cells under the Conditions of Mixed Diffusional and Migrational Mass Transport - Theory. Journal of the Electrochemical Society, 2006. 153(12): p. A2326-A2341. Papageorgiou, N., M. Grätzel, and P.P. Infelta, On the Relevance of Mass Transport in Thin Layer Nanocrystalline Photoelectrochemical Solar Cells. Solar Energy Materials and Solar Cells, 1996. 44(4): p. 405-438. W. John Albery, P.N.B., The Transport and Kinetics of Photogenerated Carriers in Colloidal Semiconductor Electrode Particles. Journal of The Electrochemical Society, 1984. 131(2): p. 315-325. Barnes, P.R.F., et al., Interpretation of Optoelectronic Transient and Charge Extraction Measurements in Dye-Sensitized Solar Cells. Advanced Materials, 2013. 25: p. 1881-1922. Kopidakis, N., et al., Ambipolar Diffusion of Photocarriers in Electrolyte-Filled, Nanoporous TiO2. Journal of Physical Chemistry B, 2000. 104(16): p. 3930-3936. Nistér, D., et al., A Detailed Analysis of Ambipolar Diffusion in Nanostructured Metal Oxide Films. Solar Energy Materials and Solar Cells, 2002. 73(4): p. 411-423. Wang, Q., et al., Cross Surface Ambipolar Charge Percolation in Molecular Triads on Mesoscopic Oxide Films. Journal of the American Chemical Society, 2005. 127(15): p. 5706-5713. Nakade, S., et al., Role of Electrolytes on Charge Recombination in Dye-Sensitized TiO2 Solar Cell (1): The Case of Solar Cells Using the I-/I3(-) Redox Couple. Journal of Physical Chemistry B, 2005. 109(8): p. 3480-3487. Fredin, K., et al., On the Influence of Anions in Binary Ionic Liquid Electrolytes for Monolithic Dye-Sensitized Solar Cells. Journal of Physical Chemistry C, 2007. 111(35): p. 13261-13266. Dloczik, L., et al., Dynamic Response of Dye-Sensitized Nanocrystalline Solar Cells: Characterization by Intensity-Modulated Photocurrent Spectroscopy. Journal of Physical Chemistry B, 1997. 101(49): p. 10281-10289. Bisquert, J. and I.n. Mora-Seró, Simulation of Steady-State Characteristics of Dye-Sensitized Solar Cells and the Interpretation of the Diffusion Length. The Journal of Physical Chemistry Letters, 2009. 1(1): p. 450-456. ‐ 122 ‐    References 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. 116. 117. 118. Wang, Q., et al., Characteristics of High Efficiency Dye-Sensitized Solar Cells. Journal of Physical Chemistry B, 2006. 110(50): p. 25210-25221. Fabregat-Santiago, F., et al., Influence of Electrolyte in Transport and Recombination in Dye-Sensitized Solar Cells Studied by Impedance Spectroscopy. Solar Energy Materials and Solar Cells, 2005. 87(1–4): p. 117-131. Fabregat-Santiago, F., et al., Electron Transport and Recombination in Solid-State Dye Solar Cell with Spiro-OMeTAD as Hole Conductor. Journal of the American Chemical Society, 2008. 131(2): p. 558-562. Niinobe, D., et al., Origin of Enhancement in Open-Circuit Voltage by Adding ZnO to Nanocrystalline SnO2 in Dye-Sensitized Solar Cells. Journal of Physical Chemistry B, 2005. 109(38): p. 17892-17900. Zhang, Z.P., et al., Influence of 4-Guanidinobutyric Acid as Coadsorbent in Reducing Recombination in Dye-Sensitized Solar Cells. Journal of Physical Chemistry B, 2005. 109(46): p. 21818-21824. Peter, L.M., et al., Transport and Interfacial Transfer of Electrons in Dye-Sensitized Nanocrystalline Solar Cells. Journal of Electroanalytical Chemistry, 2002. 524: p. 127-136. Bailes, M., et al., Determination of the Density and Energetic Distribution of Electron Traps in Dye-Sensitized Nanocrystalline Solar Cells. Journal of Physical Chemistry B, 2005. 109(32): p. 15429-15435. Boschloo, G. and A. Hagfeldt, Activation Energy of Electron Transport in Dye-Sensitized TiO2 Solar Cells. Journal of Physical Chemistry B, 2005. 109(24): p. 12093-12098. Dunn, H.K. and L.M. Peter, How Efficient Is Electron Collection in Dye-Sensitized Solar Cells? Comparison of Different Dynamic Methods for the Determination of the Electron Diffusion Length. Journal of Physical Chemistry C, 2009. 113(11): p. 4726-4731. Cao, F., et al., Electron Transport in Porous Nanocrystalline TiO2 Photoelectrochemical Cells. Journal of Physical Chemistry, 1996. 100(42): p. 17021-17027. Bisquert, J. and V.S. Vikhrenko, Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells. Journal of Physical Chemistry B, 2004. 108(7): p. 2313-2322. Bisquert, J., et al., Electron Lifetime in Dye-Sensitized Solar Cells: Theory and Interpretation of Measurements. The Journal of Physical Chemistry C, 2009. 113(40): p. 17278-17290. Papageorgiou, N., et al., J. Electrochem. Soc., 1996. 143: p. 3099. Yamanaka, N., et al., Dye-Sensitized TiO2 Solar Cells Using Imidazolium-Type Ionic Liquid Crystal Systems as Effective Electrolytes. Journal of Physical Chemistry B, 2007. 111(18): p. 4763-4769. ‐ 123 ‐    References 119. 120. 121. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. Thorsmølle, V.K., et al., Extraordinarily Efficient Conduction in a Redox-Active Ionic Liquid. ChemPhysChem, 2011. 12(1): p. 145-149. Dahms, H., Electronic Conduction in Aqueous Solution. The Journal of Physical Chemistry, 1968. 72(1): p. 362-364. Ruff, I. and V.J. Friedrich, Transfer Diffusion. I. Theoretical. The Journal of Physical Chemistry, 1971. 75(21): p. 3297-3302. Chiba, Y., et al., Dye-Sensitized Solar Cells with Conversion Efficiency of 11.1%. Japanese Journal of Applied Physics Part 2-Letters & Express Letters, 2006. 45(24-28): p. L638-L640. Kavan, L. and M. Grätzel, Highly Efficient Semiconducting TiO2 Photoelectrodes Prepared by Aerosol Pyrolysis. Electrochimica Acta, 1995. 40(5): p. 643-652. Cameron, P.J. and L.M. Peter, Characterization of Titanium Dioxide Blocking Layers in Dye-Sensitized Nanocrystalline Solar Cells. Journal of Physical Chemistry B, 2003. 107(51): p. 14394-14400. Bisquert, J., Theory of the Impedance of Electron Diffusion and Recombination in a Thin Layer. Journal of Physical Chemistry B, 2002. 106(2): p. 325-333. Fabregat-Santiago, F., et al., Characterization of Nanostructured Hybrid and Organic Solar Cells by Impedance Spectroscopy. Physical Chemistry Chemical Physics, 2011. 13(20): p. 9083-9118. Pitarch, A., et al., Electrochemical Impedance Spectra for the Complete Equivalent Circuit of Diffusion and Reaction under Steady-State Recombination Current. Physical Chemistry Chemical Physics, 2004. 6(11): p. 2983-2988. Bisquert, J., Interpretation of Electron Diffusion Coefficient in Organic and Inorganic Semiconductors with Broad Distributions of States. Physical Chemistry Chemical Physics, 2008. 10(22): p. 3175-3194. Levie, R.d., Advances in Electrochemistry and Electrochemical Engineering, 1967. 6: p. 329. Wang, P., et al., A Stable Quasi-Solid-State Dye-Sensitized Solar Cell with an Amphiphilic Ruthenium Sensitizer and Polymer Gel Electrolyte. Nature Materials, 2003. 2(6): p. 402-407. Tulloch;, J.D.M.B.S.T.G., Packaging, Scaling and Commercialization of Dye Solar Cells. Presentation at E-MRS 2009 Spring Meeting , Strasbourg , June 8, 2009. Wang, P., et al., Stable >= 8% Efficient Nanocrystalline Dye-Sensitized Solar Cell Based on an Electrolyte of Low Volatility. Applied Physics Letters, 2005. 86(12): p. 123508-3. Kopidakis, N., et al., Transport-Limited Recombination of Photocarriers in Dye-Sensitized Nanocrystalline TiO2 Solar Cells. Journal of Physical Chemistry B, 2003. 107(41): p. 11307-11315. ‐ 124 ‐    References 134. 135. 136. 137. 138. 139. 140. 141. 142. 143. 144. 145. 146. 147. 148. Ito, S., et al., Fabrication of Thin Film Dye Sensitized Solar Cells with Solar to Electric Power Conversion Efficiency over 10%. Thin Solid Films, 2008. 516(14): p. 4613-4619. Peter, L., “Sticky Electrons” Transport and Interfacial Transfer of Electrons in the Dye-Sensitized Solar Cell. Accounts of Chemical Research, 2009. 42(11): p. 1839-1847. Peter, L.M., Dye-Sensitized Nanocrystalline Solar Cells. Physical Chemistry Chemical Physics, 2007. 9(21): p. 2630-2642. Peter, L.M., Characterization and Modeling of Dye-Sensitized Solar Cells. Journal of Physical Chemistry C, 2007. 111(18): p. 6601-6612. Barnes, P.R.F., et al., Electron Injection Efficiency and Diffusion Length in Dye-Sensitized Solar Cells Derived from Incident Photon Conversion Efficiency Measurements. Journal of Physical Chemistry C, 2009. 113(3): p. 1126-1136. Barnes, P.R.F., et al., Re-Evaluation of Recombination Losses in Dye-Sensitized Cells: The Failure of Dynamic Relaxation Methods to Correctly Predict Diffusion Length in Nanoporous Photoelectrodes. Nano Letters, 2009. 9(10): p. 3532-3538. Lobato, K., L.M. Peter, and U. Wurfel, Direct Measurement of the Internal Electron Quasi-Fermi Level in Dye Sensitized Solar Cells Using a Titanium Secondary Electrode. Journal of Physical Chemistry B, 2006. 110(33): p. 16201-16204. Muller, P., Glossary of Terms Used in Physical Organic Chemistry (Iupac Recommendations 1994). Pure Appl. Chem, 1994. 66(5): p. 1077-1184. Hardin, B.E., H.J. Snaith, and M.D. McGehee, The Renaissance of Dye-Sensitized Solar Cells. Nat Photon, 2012. 6(3): p. 162-169. Falaras, F., T. Stergiopoulos, and D.S. Tsoukleris, Enhanced Efficiency in Solid-State Dye-Sensitized Solar Cells Based on Fractal Nanostructured TiO2 Thin Films. Small, 2008. 4(6): p. 770-776. Schmidt-Mende, L., S.M. Zakeeruddin, and M. Grätzel, Efficiency Improvement in Solid-State-Dye-Sensitized Photovoltaics with an Amphiphilic Ruthenium-Dye. Applied Physics Letters, 2005. 86(1). Sinke, W.C. and M.M. Wienk, Photochemistry - Solid-State Organic Solar Cells. Nature, 1998. 395(6702): p. 544-545. Chen, P., et al., High Open-Circuit Voltage Solid-State Dye-Sensitized Solar Cells with Organic Dye. Nano Letters, 2009. 9(6): p. 2487-2492. Burschka, J., et al., tris(2-(1h-pyrazol-1-yl)Pyridine)Cobalt(II) as P-Type Dopant for Organic Semiconductors and Its Application in Highly Efficient Solid-State Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2011. 133(45): p. 18042-18045. Bach, U., et al., Solid-State Dye-Sensitized Mesoporous TiO2 Solar Cells with High Photon-to-Electron Conversion Efficiencies. Nature, 1998. 395(6702): p. 583-585. ‐ 125 ‐    References 149. 150. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. Poplavskyy, D., Nondispersive Hole Transport in Amorphous Films of Methoxy-Spirofluorene-Arylamine Organic Compound. J. Appl. Phys., 2003. 93(1): p. 341. Ding, I.K., et al., Pore-Filling of Spiro-OMeTAD in Solid-State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device Performance. Advanced Functional Materials, 2009. 19(15): p. 2431-2436. Snaith, H.J., et al., Charge Collection and Pore Filling in Solid-State Dye-Sensitized Solar Cells. Nanotechnology, 2008. 19(42). Koh, J.K., et al., Highly Efficient, Iodine-Free Dye-Sensitized Solar Cells with Solid-State Synthesis of Conducting Polymers. Advanced Materials, 2011. 23(14): p. 1641-1646. Wang, Q., et al., Constructing Ordered Sensitized Heterojunctions: Bottom-up Electrochemical Synthesis of P-Type Semiconductors in Oriented n-TiO2 Nanotube Arrays. Nano Letters, 2009. 9(2): p. 806-813. Sun, L., et al., Fabrication of TiO2/CuSCN Bulk Heterojunctions by Profile-Controlled Electrodeposition. Journal of The Electrochemical Society, 2012. 159(5): p. D323-D327. Wang, M., et al., Surface Design in Solid-State Dye Sensitized Solar Cells: Effects of Zwitterionic Co-Adsorbents on Photovoltaic Performance. Advanced Functional Materials, 2009. 19(13): p. 2163-2172. Palomares, E., et al., Control of Charge Recombination Dynamics in Dye Sensitized Solar Cells by the Use of Conformally Deposited Metal Oxide Blocking Layers. Journal of the American Chemical Society, 2003. 125(2): p. 475-482. Palomares, E., et al., Slow Charge Recombination in Dye-Sensitised Solar Cells (Dssc) Using Al2O3 Coated Nanoporous TiO2 Films. Chemical Communications, 2002(14): p. 1464-1465. Kruger, J., et al., High Efficiency Solid-State Photovoltaic Device Due to Inhibition of Interface Charge Recombination. Applied Physics Letters, 2001. 79(13): p. 2085-2087. Horiuchi, T., et al., High Efficiency of Dye-Sensitized Solar Cells Based on Metal-Free Indoline Dyes. Journal of the American Chemical Society, 2004. 126(39): p. 12218-12219. Schmidt-Mende, L., et al., Organic Dye for Highly Efficient Solid-State Dye-Sensitized Solar Cells. Advanced Materials, 2005. 17(7): p. 813-815. Cid, J.-J., et al., Molecular Cosensitization for Efficient Panchromatic Dye-Sensitized Solar Cells. Angewandte Chemie International Edition, 2007. 46(44): p. 8358-8362. Hardin, B.E., et al., Increased Light Harvesting in Dye-Sensitized Solar Cells with Energy Relay Dyes. Nat Photon, 2009. 3(7): p. 406-411. Siegers, C., et al., A Dyadic Sensitizer for Dye Solar Cells with High Energy-Transfer Efficiency in the Device. Chemphyschem, 2007. 8(10): p. 1548-1556. ‐ 126 ‐    References 164. 165. 166. 167. 168. 169. 170. 171. 172. 173. 174. 175. 176. 177. Standridge, S.D., G.C. Schatz, and J.T. Hupp, Distance Dependence of Plasmon-Enhanced Photocurrent in Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2009. 131(24): p. 8407-8409. Brown, M.D., et al., Plasmonic Dye-Sensitized Solar Cells Using Core−Shell Metal−Insulator Nanoparticles. Nano Letters, 2010. 11(2): p. 438-445. Ding, I.K., et al., Plasmonic Dye-Sensitized Solar Cells. Advanced Energy Materials, 2011. 1(1): p. 52-57. Fabregat-Santiago, F., et al., Correlation between Photovoltaic Performance and Impedance Spectroscopy of Dye-Sensitized Solar Cells Based on Ionic Liquids. Journal of Physical Chemistry C, 2007. 111(17): p. 6550-6560. Liu, Y., et al., Cobalt Redox Mediators for Ruthenium-Based Dye-Sensitized Solar Cells: A Combined Impedance Spectroscopy and near-IR Transmittance Study. The Journal of Physical Chemistry C, 2011. 115(38): p. 18847-18855. Adachi, M., et al., Determination of Parameters of Electron Transport in Dye-Sensitized Solar Cells Using Electrochemical Impedance Spectroscopy. The Journal of Physical Chemistry B, 2006. 110(28): p. 13872-13880. Zhu, K., S.-R. Jang, and A.J. Frank, Impact of High Charge-Collection Efficiencies and Dark Energy-Loss Processes on Transport, Recombination, and Photovoltaic Properties of Dye-Sensitized Solar Cells. The Journal of Physical Chemistry Letters, 2011. 2(9): p. 1070-1076. Fabregat-Santiagoa, F., et al., Impedance Spectroscopy Study of Dye-Sensitized Solar Cells with Undoped Spiro-OMeTAD as Hole Conductor. Journal of Applied Physics, 2006. 100: p. 034510. Hendry, E., et al., Local Field Effects on Electron Transport in Nanostructured TiO2 Revealed by Terahertz Spectroscopy. Nano Letters, 2006. 6(4): p. 755-759. Kron, G., et al., Electronic Transport in Dye-Sensitized Nanoporous TiO2 Solar Cells-Comparison of Electrolyte and Solid-State Devices. Journal of Physical Chemistry B, 2003. 107(15): p. 3556-3564. Snaith, H.J. and M. Grätzel, Electron and Hole Transport through Mesoporous TiO2 Infiltrated with Spiro- MeOTAD. Advanced Materials, 2007. 19(21): p. 3643-3647. Garcia-Belmonte, G., et al., Anomalous Transport on Polymeric Porous Film Electrodes in the Dopant-Induced Insulator-to-Conductor Transition Analyzed by Electrochemical Impedance. Applied Physics Letters, 2001. 78(13): p. 1885-1887. Gevorgian, S. and H. Berg. Line Capacitance and Impedance of Coplanar-Strip Waveguides on Substrates with Multiple Dielectric Layers. in Microwave Conference, 2001. 31st European. 2001. Wang, Q., et al., Molecular Wiring of Nanocrystals: NCS-Enhanced Cross-Surface Charge Transfer in Self-Assembled Ru-Complex Monolayer on Mesoscopic Oxide Films. Journal of the American Chemical Society, 2006. 128(13): p. 4446-4452. ‐ 127 ‐    References 178. 179. 180. 181. 182. 183. 184. 185. 186. 187. 188. 189. 190. 191. Cappel, U.B., T. Daeneke, and U. Bach, Oxygen-Induced Doping of Spiro-MeOTAD in Solid-State Dye-Sensitized Solar Cells and Its Impact on Device Performance. Nano Letters, 2012. 12(9): p. 4925-4931. Abate, A., et al., Lithium Salts as "Redox Active" P-Type Dopants for Organic Semiconductors and Their Impact in Solid-State Dye-Sensitized Solar Cells. Physical Chemistry Chemical Physics, 2013. 15(7): p. 2572-2579. van de Lagemaat, J. and A.J. Frank, Effect of the Surface-State Distribution on Electron Transport in Dye-Sensitized TiO2 Solar Cells:  Nonlinear Electron-Transport Kinetics. The Journal of Physical Chemistry B, 2000. 104(18): p. 4292-4294. Fisher, A.C., et al., Intensity Dependence of the Back Reaction and Transport of Electrons in Dye-Sensitized Nanacrystalline TiO2 Solar Cells. Journal of Physical Chemistry B, 2000. 104(5): p. 949-958. Bisquert, J., Chemical Diffusion Coefficient of Electrons in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells. The Journal of Physical Chemistry B, 2004. 108(7): p. 2323-2332. Bisquert, J., Hopping Transport of Electrons in Dye-Sensitized Solar Cells. Journal of Physical Chemistry C, 2007. 111(46): p. 17163-17168. Garcia-Canadas, J., et al., Determination of Electron and Hole Energy Levels in Mesoporous Nanocrystalline TiO2 Solid-State Dye Solar Cell. Synthetic Metals, 2006. 156(14-15): p. 944-948. Natarajan, A., G. Oskam, and P.C. Searson, The Potential Distribution at the Semiconductor/Solution Interface. The Journal of Physical Chemistry B, 1998. 102(40): p. 7793-7799. Jennings, J.R., Y. Liu, and Q. Wang, Efficiency Limitations in Dye-Sensitized Solar Cells Caused by Inefficient Sensitizer Regeneration. The Journal of Physical Chemistry C, 2011. 115(30): p. 15109-15120. Barnes, P.R.F., et al., Simulation and Measurement of Complete Dye Sensitised Solar Cells: Including the Influence of Trapping, Electrolyte, Oxidised Dyes and Light Intensity on Steady State and Transient Device Behaviour. Physical Chemistry Chemical Physics, 2011. 13: p. 5798-5816. Zhang, Z., et al., Influence of Iodide Concentration on the Efficiency and Stability of Dye-Sensitized Solar Cell Containing Non-Volatile Electrolyte. ChemPhysChem, 2009. 10(11): p. 1834-1838. Haque, S.A., et al., Charge Recombination Kinetics in Dye-Sensitized Nanocrystalline Titanium Dioxide Films under Externally Applied Bias. Journal of Physical Chemistry B, 1998. 102(10): p. 1745-1749. Chen, C.-Y., et al., Ruthenium Sensitizer with Thienothiophene-Linked Carbazole Antennas in Conjunction with Liquid Electrolytes for Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 2011. 115(40): p. 20043-20050. Wang, Q., et al., Molecular Wiring of Nanocrystals:  NCS-Enhanced Cross-Surface Charge Transfer in Self-Assembled Ru-Complex Monolayer on ‐ 128 ‐    References Mesoscopic Oxide Films. Journal of the American Chemical Society, 2006. 128(13): p. 4446-4452. Salvador, P., et al., Illumination Intensity Dependence of the Photovoltage in Nanostructured TiO2 Dye-Sensitized Solar Cells. Journal of Physical Chemistry B, 2005. 109(33): p. 15915-15926. Liu, Y., et al., Heterogeneous Electron Transfer from Dye-Sensitized Nanocrystalline TiO2 to [Co(Bpy)3]3+: Insights Gained from Impedance Spectroscopy. Journal of the American Chemical Society, 2013. 135(10): p. 3939-3952. Ansari-Rad, M., J.A. Anta, and J. Bisquert, Interpretation of Diffusion and Recombination in Nanostructured and Energy-Disordered Materials by Stochastic Quasiequilibrium Simulation. The Journal of Physical Chemistry C, 2013. Papageorgiou, N., C. Barbe, and M. Grätzel, Morphology and Adsorbate Dependence of Ionic Transport in Dye Sensitized Mesoporous TiO2 Films. Journal of Physical Chemistry B, 1998. 102(21): p. 4156-4164. Wang, M., et al., The Influence of Charge Transport and Recombination on the Performance of Dye-Sensitized Solar Cells. ChemPhysChem, 2009. 10(1): p. 290-299. Bai, Y., et al., High-Performance Dye-Sensitized Solar Cells Based on Solvent-Free Electrolytes Produced from Eutectic Melts. Nature Materials, 2008. 7(8): p. 626-630. Zhang, X., J. Leddy, and A.J. Bard, Dependence of Rate Constants of Heterogeneous Electron Transfer Reactions on Viscosity. Journal of the American Chemical Society, 1985. 107(12): p. 3719-3721. Halme, J., et al., Device Physics of Dye Solar Cells. Advanced Materials, 2010. 22(35): p. E210-E234. 192. 193. 194. 195. 196. 197. 198. 199.     ‐ 129 ‐    Publications Publications 1. Li, F., J.R. Jennings, and Q. Wang, Determination of Sensitizer Regeneration Efficiency in Dye-Sensitized Solar Cells. ACS Nano, 2013. 7(9): p. 8233-8242. 2. Li, F.; Jennings, J. R.; Wang, Q.; Chua, J.; Mathews, N.; Mhaisalkar, S. G.; Moon, S.-J.; Zakeeruddin, S. M.; Grätzel, M., Determining the Conductivities of the Two Charge Transport Phases in Solid-State Dye-Sensitized Solar Cells by Impedance Spectroscopy. The Journal of Physical Chemistry C 2013, 117 (21), 10980-10989. 3. Li, F.; Jennings, J. R.; Mathews, N.; Wang, Q., Evolution of Charge Collection / Separation Efficiencies in Dye-Sensitized Solar Cells Upon Aging: A Case Study. Journal of The Electrochemical Society 2011, 158 (9), B1158-B1163. 4. Jennings, J. R.; Li, F.; Wang, Q., Reliable Determination of Electron Diffusion Length and Charge Separation Efficiency in Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C 2010, 114 (34), 14665-14674. 5. Zhang, W.; Zhu, R.; Li, F.; Wang, Q.; Liu, B., High-Performance Solid-State Organic Dye Sensitized Solar Cells with P3HT as Hole Transporter. The Journal of Physical Chemistry C 2011, 115 (14), 7038-7043. 6. Xingzhu Wang, Jing Yang, Hao Yu, Feng Li, Li Fan, Dawei Zhang, Yeru Liu, Zhen Yu Koh, Jiahong Pan, Lei Yan and Qing Wang, Benzothiazole-cyclopentadithiophene Bridged D-A-π-A Organic Sensitizer with Enhanced NIR Light Absorption for Efficient Dye-sensitized Solar Cells, chem. comn., accepted. Conferences: ‐ 130 ‐    Publications 7. Li, F.; Jennings, J. R.; Wang, Q., Dye Regeneration under Working Conditions in Dye-Sensitized Solar Cell, HOPV 13, Seville, Spain. 8. Li, F.; Jennings, J. R.; Mhaisalkar, S. G.;Wang, Q., Influence of supporting electrolyte concentration on photocurrent of dye-sensitized solar cells employing robust electrolytes, ICMAT 2011, Singapore. 9. Li, F.; Jennings, J. R.; Wang, Q., Quantifying Dye Regeneration Efficiency in Dye-sensitized Solar Cells at Operating Conditions, ICMAT 2013, Singapore. Manuscript in progress: 10. Feng Li, James Robert Jennings, Xingzhu Wang, Li Fan, Zhen Yu Koh, Lei Yan, Hao Yu and Qing Wang, Influence of electrolyte ionic strength and viscosity on recombination and regeneration kinetics in dye-sensitized solar cells, submitted, invited article to The Journal of Physical Chemistry C for Prof. Michael Grätzel Festschrift.   ‐ 131 ‐    [...]... change EER reaction order in total electron concentration charge collection efficiency electron injection efficiency light harversting efficiency dye regeneration efficiency charge separation efficiency λ wavelength free electron lifetime effective electron lifetime angular frequency ‐ 11 ‐    List of Figures and Tables   Figure 1-1 Typical structure of DSCs Figure 1-2 Major charge transfer and transport... motivation and introduction of this work 1.2 Basic Concept and Working Principles of DSCs As mentioned in the previous section, DSCs are a promising challenger to the conventional photovoltaics They can be classified as excitonic solar cells because charge carriers are generated and separated simultaneously across a heterointerface upon excitation.[11, 12] Thus the created excitons are dissociated before... with the IS and differential IPCE Lastly, it must be noted here as the focus of my work is the charge separation and collection in mesoscopic systems Little effort has been done to actually optimize the PCE of the devices, and this may be addressed in the future, which is included in the conclusion and outlook section with more details ‐ 22 ‐    Chapter 2 Chapter 2 Models for Charge Transport and Transfer... to expect the interaction between them during diffusion, which is known as ambipolar diffusion and the ambipolar diffusion coefficient of electrons is: / where is the ambipolar diffusion coefficient, electrons and counter ions, and In DSCs under typical conditions, and thus between (2.16) / and are the concentration of are the corresponding diffusion coefficients [98-100] (∼3 × 1020 cm-3) is much higher... DSCs Figure 4-3 Evolution of thermodynamic and kinetic parameters obtained from IS Figure 4-4 Evolution of and Figure 4-5 Normal and 1-Sun IPCE of fresh and aged DSCs; predicted and measured ; mono IPCE of the fresh cells and corresponding differential IPCE at 627 nm Figure 4-6 Evolution of upon aging, determined from normal IPCE and 1-Sun IPCE Figure 4-7 OC IPCE, and / versus for selected aging times;... discussed in Chapter 6 2.2 Dye regeneration As mentioned previously, DSCs can be considered as excitonic solar cells For a complete charge separation process, a “hole injection” procedure coupled with the electron injection is naturally expected This “hole injection” process in DSCs is termed as dye regeneration (refer to Fig 2-2), as the oxidized dye molecules are reduced and return to the original ground... basis for the diffusion oriented charge transport is the high concentration of counter ions in the electrolyte (c.a 0.1~1 M, much larger than and the total electron concentration away from the electrons ( , as will be discussed later.) only nanometers dybye length of electrons), which effectively screen the negative charge in the TiO2 With such short distances, it is reasonable to expect the interaction... external contact and mechanical support for the electrode; and in order to improve interconnection among particles and adhesion to the substrate, nanoparticle electrodes are often sintered and heat treated, whereas nanorod and nanotube based electrodes can be grown directly and continuously on appropriate substrates [16, 17] Given the unique nature of DSCs (photons harvested by sensitizers), semiconductors... be elaborated Under illumination, sensitizers are excited by photons with certain energy [excitation, route (1)] and become oxidized after injecting electrons into the vacant electronic states (conduction band states) of semiconductor film [electron injection, route (2)], which usually occurs on a sub-picosecond timescale [49] Whereas it must be admitted that relaxation of excited dye molecules [route... 2.9-2.11 only describes the regeneration using I /I ‐ 28 ‐    and do not Chapter 2 apply to other redox mediators such cobalt complexes, ferrocene derivatives and HTM.[36, 41, 80, 81] Based on the reaction mechanisms and the continuity equations of free electrons and oxidized dye molecules, , which is independent of I , can be derived [51]: I (2.12) I where and are the rate constants for dye regeneration . ‐1‐    Study on Charge Separation and Collection for stable mesoscopic sensitized solar cells Li Feng (Bachelor of Eng, SJTU) A thesis submitted for the degree of Doctor. Absorption Spectroscopy ‐  42‐ 3.2.5 Other Characterization Techniques. ‐  44‐ ‐5‐  Chapter 4. Evolution of Charge Collection / Separation Efficiencies in Dye -sensitized Solar Cells upon. transient and steady-state approaches. ‐81‐ 6.3.2 Dependence of electron concentration on photon flux in regular and inert cells.  ‐ 89‐ 6.3.3 Dependence of EDR rate constant on electron concentration