Membrane separators for back contact DSSCs at UNSW
Dr Jaleh Mansouri, UNSW, with the force spinning machine
The back contact dye sensitised solar cell (BCDSSC) requires a separator to prevent physical contact between the photo-anode and the counter electrode while permitting free ion flow. Therefore, highly porous/wettable polymer separator films are required to reduce mass transfer limitations for electrolyte species. Commercial polymeric membranes can have low porosity, wettability and electrolyte uptake. To improve the performance of the BCDSSC, CRC-P research led by Professor Vicki Chen from the UNESCO Centre for Membrane Science and Technology at the University of New South Wales has been exploiting unique characteristics of polymeric nanofibre membranes with inorganic particles to form ultrathin and highly wettable nonwoven separators fabricated by force spinning techniques.
A nanofibre web produced from solution and formed on collectors
Until recently, polymeric nanofibres were mainly made by electrospinning (ES) techniques. Unlike ES, which draws fibres through the use of electrostatic forces, force spinning (FS) uses centrifugal forces that allow for a significant increase in yield and ease of production. No electric fields are needed; therefore, restrictions imposed on materials with low dielectric constants (e.g. fluoropolymers) are eliminated. Also, FS has the distinct advantage of being able to produce nanofibres from both polymeric solutions and melts. Fibre morphology and diameter are controlled by the operating parameters such as: solution concentration, melt viscosity (for melt spinning), rotational speed of the spinneret, orifice size, temperature of the spinneret and the collection system.
A series of non-woven mats with nanofibres in the range of sub-microns to a couple of microns were fabricated with force spinning technology using fluoropolymers and nanoparticles. The thickness of non-woven mats can be controlled by varying the amount of solution and post-treatment conditions. These nanofibre separators are being evaluated for use in BCDSSC cells, and the technology may be similarly applied to other applications such as battery separators and spacers.
Figures above: Nanofibres spun from a fluoropolymer and inorganic additives
