Dye sensitised solar cells (DSCs) typically include a mesoporous titanium dioxide (TiO2) scaffold, sensitised with an adsorbed dye, as the main active element responsible for the photon absorption and charge separation functionalities. The sintering process employed in the TiO2 active layer fabrication plays a crucial role in the formation of the nanoparticle (NP) scaffold and hence in the performance of a dye sensitised solar cell, as it allows the particles to form efficient inter-crystalline electric contacts providing high electron conductivity. Furthermore, the DSC design requires a conductive transparent top electrode which is typically made of fluorinated stannic oxide. Here we report on a highly spatially resolved scanning electron microscopy study in conjunction with focussed ion beam milling and energy dispersive X-ray (EDX) mapping of the distribution of all relevant elements within a DSC subsequent to a classical sintering process in the range of 350°C–550°C. Additionally, the article provides quantitative results regarding the found Sn diffusion and its effect on efficiency confirmed via J-V measurements. The effective spatial resolution of the EDX studies was calculated by Monte Carlo simulations of the electron trajectories and X-ray emission region. This permits to construct a model for the migration of Sn from the transparent conductive oxide into the TiO2 scaffold, resulting in alterations in the composition of the complex system which has a direct effect on the DSC performance. J-V measurements conclude that sintering temperature of 500°C is close to the optimum regarding Sn diffusion enhancement of DSCs. Sintering temperatures above 500°C were causing a drop in the DSC efficiency and are therefore not recommended. In order to optimize the DSC efficiency, the results are summarized by a model that explains how the efficiency varies with the Sn diffusion process.
References
[1]
O’Regan B, Gr？tzel M (1991) A low-cost high effiiciency solar cell based on dye-sensitised colloidal titanium dioxide films. Nature 335: 737–739.
[2]
Yella A, Lee HW, Tsao HN, Yi C, Chandiran AK, et al. (2011) Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency. Science 334: 629–634.
[3]
Gerischer H, Tributsch H (1968) Elektrochemische Untersuchungen zur spektralen Sensibilisierung von ZnO-Einkristallen. Ges. Phys.Chem. 72: 437–445.
[4]
Tsubomura H, Matsumura M, Nomura Y, Amamiya T (1976) Dye sensitised zinc oxide: aqueous electrolyte: platinum photocell. Nature 261, 402–403.
[5]
Dare-Edwards MP, Goodenough JB, Hamnet A, Seddon KR, Wright RD (1980) Sensitisation of semiconducting electrodes with ruthenium-based Dyes. Faraday Discuss. Chem. Soc. 70: 285–298.
[6]
Duonghong D, Serpone N, Gr？tzel M (1984) Integrated systems for water cleavage by visible light; Sensitization of TiO2 particles by surface derivatization with ruthenium complexes. Helv. Chim. Acta 67: 1012–1018.
[7]
Desilvestro J, Gr？tzel M, Kavan L, Moser JE, Augustynski J (1985) Highly efficient sensitization of titanium dioxide. J. Am. Chem. Soc. 107: 2988–2990.
[8]
Namba S, Hishiki Y (1965) Color sensitization of zinc oxide with cyanine dyes. J. Phys. Chem. 69: 774–779.
[9]
Vlachopoulos N, Liska P, Augustynski J, Gr？tzel M (1988) Very efficient visible light energy harvesting and conversion by spectral sensitization of high surface area polycrystalline titanium dioxide films. J. Am. Chem. Soc. 110: 1216–1220.
[10]
Nazeeruddin MK, Kay A, Rodicio I, Humpbry-Baker R, Miiller E, et al. (1993) Conversion of light to electricity by cis-X2bis(2,2′-bipyridyl-4,4′-dicarboxyl？ate)ruthenium(II)charge-transfer sensitizers (X = Cl-, Br-, I-, CN-, and SCN-) on nanocrystalline titanium dioxide electrodes. J. Am. Chem. Soc. 115: 6382–6390.
[11]
Nazeeruddin MK, Pechy P, Gr？tzel M (1997) Efficient panchromatic sensitization of nanocrystalline TiO2 films by a black dye based on a trithiocyanato-ruthenium complex. Chem. Commun. 1: 1705–1706.
[12]
Green MA, Emery K, Hishikawa Y, Warta W (2009) Solar cell efficiency tables (version 34). Prog. Photovolt.: Res. Appl. 17: 85.
[13]
Pechy P, Rotzinger F, Nazeeruddin MK, Kohle O, Zakeeruddin SM, et al. (1995) Preparation of phosphonated polypyridyl ligands to anchor transition-metal complexes on oxide surfaces: application for the conversion of light to electricity with nanocrystalline TiO2 films. Chem. Commun. 1: 65–66.
[14]
Tachibana Y, Haque SA, Mercer IP, Moser JE, Klug DR, et al. (2001) Modulation of the rate of electron injection in dye sensitised nanocrystalline TiO2 films by externally applied bias. J. Phys. Chem. B 105: 7424–7431.
[15]
Nazeeruddin MK, Humphry-Baker R, Liska P, Gr？tzel M (2003) Investigation of sensitizer adsorption and the influence of protons on current and voltage of a dye-sensitized nanocrystalline TiO2 solar cell. J. Phys. Chem. B 107: 8981–8987.
[16]
Chiba Y, Islan A, Watanabe Y, Komiya R, Koida N, et al. (2006) Dye-sensitized solar cells with conversion efficiency of 11.1%. Jpn. J. App. Phys. 45: 638–640.
[17]
Shi D, Pootrakuchote N, Li R, Guo J, Wang Z, et al. (2008) New efficiency records for stable dye-sensitized solar cells with low-volatility and ionic liquid electrolytes. J. Phys. Chem. C 112: 17046–17050.
[18]
Ito S, Liska P, Comte P, Charvet R, Pechy P, et al. (2005) Control of dark current in photoelectrochemical (TiO2/I–I3？) and dye-sensitized solar cells. Chem. Commun. 34: 4351–4353.
[19]
Brown MD, Suteewong T, Kumar RS, D’Innocenzo V, Petrozza A, et al. (2011) Plasmonic Dye-Sensitized Solar Cells Using Core-Shell Metal-Insulator. Nanoparticles Nano Lett. 11: 438–445.
[20]
Andrei C, Lestini E, Crosbie S, de Frein C, O’Reilly T, et al.. (2013) Plasmonic enhanced dye sensitised solar cells via chemical functionalisation of gold nanoparticles, Adv. En. Mat.: in press.
[21]
Doyle G, Ashall B, Galvin M, Berndt M, Crosbie S, et al. (2007) Mie scattering and surface plasmon based spectroscopy for the detection of nanoparticle-protein interaction. Appl. Phys. A. 89: 351–355.
[22]
Williamson A, McClean E, Leipold D, Zerulla D, Runge E (2011) The design of efficient surface-plasmon-enhanced ultra-thin polymer-based solar cells. Appl. Phys. Lett. 99: 093307–093310.
[23]
Kamat PV (2008) Quantum dot solar cells - Semiconductor nanocrystals as light harvesters. J. Phys. Chem. C 112: 18737–18753.
[24]
Ito S, Murakami TN, Comte P, Liska P, Gr？tzel C, et al. (2008) Fabrication of thin film dye sensitized solar cells with solar to electric power conversion efficiency over 10%. Thin Solid Films 516: 4613–4619.
[25]
Gr？tzel M (2004) Conversion of sunlight to electric power by nanocrystalline dye-sensitised solar cells. J. of Photochem. and Photobiol. A 164: 3–14.
[26]
Zhu K, Kopidakis N, Neale NR, van de Lagemaat J, Frank AJ (2006) Influence of surface area on charge transport and recombination in dye-sensitized TiO2 solar cells. J. Phys. Chem. B 110: 25174–25180.
[27]
Lin J, Yu JC, Lo J, Lan SK (1999) Photocatalytic activity of rutile Ti1？xSnxO2 solid solutions. J. Catal. 183: 368–372.
[28]
Zheng SK, Wang TM, Hao WC, Shen R (2002) Improvement of photocatalytic activity of TiO2 thin film by Sn ion implantation. Vacuum 65: 155–159.
[29]
Cao Y, Yang W, Zhang W, Liu G, Yue P (2004) Improved photocatalytic activity of Sn4+ doped TiO2 nanoparticulate films prepared by plasma-enhanced chemical vapor deposition. New J. Chem. 2: 218–222.
[30]
Do YR, Lee W, Dwight K, Wold A (1994) The effect of WO3 on the photocatalytic activity of TiO2. J. Solid State Chem. 108: 198–201.
[31]
Duan Y, Fu N, Liu Q, Fang Y, Zhou X, et al. (2012) Sn-doped TiO2 photoanode for dye-sensitized solar cells. J. Phys. Chem. C 116: 8888–8893.
[32]
Xin B, Ding D, Gao Y, Jin X, Fu H, et al. (2009) Preparation of nanocrystalline Sn–TiO2？X via a rapid and simple stannous chemical reducing route. Appl. Surf. Sci. 255: 5896–5901.
[33]
Andrei C, O’Reilly T, Zerulla D (2010) A spatially resolved study on the Sn diffusion during the sintering process in the active layer of dye sensitised solar cells. Phys. Chem. Chem. Phys. 12: 7241–7245.
[34]
Ottermann C, Otto J, Jeschkowski U, Anderson O, Fleming M, et al. (1993) Stress of TiO2 thin films produced by different deposition techniques. Mater. Res. Soc. Symp. Proc. 308: 69.
[35]
Smestad GP, Gr？tzel M (1998) Demonstrating Electron Transfer and Nanotechnology: A Natural Dye-Sensitized Nanocrystalline Energy Converter. J. Chem. Ed. 75: 752–756.
[36]
Drouin XD, Couture AR, Joly D, Tastet X, Aimez V, et al. (2007) A fast and easy-to-use modeling tool for scanning electron microscopy and microanalysis users. Scanning 29: 92–101.
[37]
Meen TH, Water W, Chen WR, Chao SM, Ji LW, et al. (2009) Application of TiO2 nano-particles on the electrode of dye-sensitized solar cells. J. Phys. and Chem. of Sol. 70: 472–476.
