Interconnecting dye solar cells in modules—I–V characteristics under reverse bias

Abstract The upscaling of the dye solar cell (DSC) technology involves a series connection of single cells to form modules. Thus an utilisable voltage is reached. In an outdoor situation, one or more cells connected in series might be shaded. The shaded cells then have to transport the current of the module in reverse bias. Here, a study of the processes and interfaces involved in the electron transport of a DSC under reverse bias is presented. Furthermore, the effect of these processes on the long-term stability of a DSC is evaluated. The I – V characteristic of a DSC under reverse bias differs significantly from a typical diode I – V characteristic. Compared to other solar cell technologies, in particular crystalline silicon solar cells, the largest sustainable reversed biased voltage (breakdown voltage) of a DSC is extremely low (approximately 500 mV). Therefore, in terms of power output, no bypass diodes are required, when connecting DSC in series. In order to identify the processes and the interfaces involved in the charge carrier transport in reverse bias, a batch of different electrode set-ups was built that consisted of single components of a standard DSC. It was shown that charge transport under reverse bias directly occurs via the electrolyte/TCO (transparent conducting oxide) interface, catalysed by the dye molecules. The charge transfer is highly asymmetrical, with a symmetry parameter of approximately 0.35, using a simple Butler-Vollmer model. Electrical impedance spectroscopy revealed that the TiO 2 -layer is not significantly involved in the electron transport under reverse bias. To study the effect of reverse biasing on the long-term stability of DSC, solar cells were subjected to a constant reverse current in the dark for more than 100 h. The voltage drop over the cell was monitored. It increased only slightly, without reaching critical values, which would damage the cell irreversibly. No degradation in overall efficiency was observed for more than 100 h.

[1]  Anders Hagfeldt,et al.  Theoretical Models for the Action Spectrum and the Current-Voltage Characteristics of Microporous Semiconductor Films in Photoelectrochemical Cells , 1994 .

[2]  G. Tulloch,et al.  Light and energy—dye solar cells for the 21st century , 2004 .

[3]  Laurence M. Peter,et al.  Characterization of titanium dioxide blocking layers in dye-sensitized nanocrystalline solar cells , 2003 .

[4]  F. Willig,et al.  Origin of Photovoltage and Photocurrent in the Nanoporous Dye-Sensitized Electrochemical Solar Cell , 1999 .

[5]  Yasuhiko Takeda,et al.  Outdoor performance of large scale DSC modules , 2004 .

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

[7]  Fei Cao,et al.  ELECTRON TRANSPORT IN POROUS NANOCRYSTALLINE TIO2 PHOTOELECTROCHEMICAL CELLS , 1996 .

[8]  Yang Huang,et al.  Dye-sensitized solar cells, from cell to module , 2004 .

[9]  Nathan S. Lewis,et al.  Current Density versus Potential Characteristics of Dye-Sensitized Nanostructured Semiconductor Photoelectrodes. 1. Analytical Expressions , 2004 .

[10]  Joachim Luther,et al.  Modeling of Photovoltage and Photocurrent in Dye-Sensitized Titanium Dioxide Solar Cells , 2001 .

[11]  J. Ferber,et al.  An electrical model of the dye-sensitized solar cell , 1998 .

[12]  Jenny Nelson,et al.  Continuous-time random-walk model of electron transport in nanocrystalline TiO 2 electrodes , 1999 .

[13]  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.

[14]  Martin A. Green,et al.  Solar cell efficiency tables (Version 31) , 2008 .

[15]  Michael Grätzel,et al.  Electrochemical studies of the Co(III)/Co(II)(dbbip)2 redox couple as a mediator for dye-sensitized nanocrystalline solar cells , 2004 .

[16]  Joachim Luther,et al.  Modeling and interpretation of electrical impedance spectra of dye solar cells operated under open-circuit conditions , 2002 .

[17]  Laurence M. Peter,et al.  Dynamic Response of Dye-Sensitized Nanocrystalline Solar Cells: Characterization by Intensity-Modulated Photocurrent Spectroscopy , 1997 .

[18]  Andreas F. Meyer,et al.  Long‐term stability of dye‐sensitised solar cells , 2001 .

[19]  Michael Grätzel,et al.  Perspectives for dye‐sensitized nanocrystalline solar cells , 2000 .

[20]  Hiroshi Matsui,et al.  100 mm × 100 mm large-sized dye sensitized solar cells , 2004 .

[21]  Sarmimala Hore,et al.  How important is the back reaction of electrons via the substrate in dye-sensitized nanocrystalline solar cells? , 2005, The journal of physical chemistry. B.

[22]  On the modeling of the dye-sensitized solar cell , 1998 .

[23]  P. M. Sommeling,et al.  Reproducible manufacturing of dye‐sensitized solar cells on a semi‐automated baseline , 2003 .

[24]  Yang Huang,et al.  Design of DSC panel with efficiency more than 6 , 2005 .

[25]  Shunichiro Ito,et al.  Multi-colored dye-sensitized solar cells , 2004 .