LOW COST SOLID AND QUASI-SOLID ELECTROLYTES FOR PHOTOELECTROCHEMICAL SOLAR CELLS

摘要

The photoelectrochemical (also known as Graetzel) cell, offers an attractive and potentially low cost alternative to conventional semiconductor based solar cells [1]. Currently, although such devices offer many advantages in terms of low cost materials and manufacture, it would be desirable to further reduce costs and increase stability. Two of the most significant sources of manufacturing costs and complexity in these devices, is in the use of costly transparent conductive coated glass as substrates for the device and in effecting hermetic sealing of the volatile liquid electrolytes conventionally used. Substitution of the liquid electrolytes by solid state analogues might allow both the sealing step to be eliminated and facilitate the development of lower cost flexible cells based on polymer substrates provided that such cells could be produced without the requirement for high temperature sintering heat treatment. In this work, one approach is described by which such low cost flexible cells might be realised, through the use of low cost solid electrolytes. The redox electrolyte used in conventional photoelectrochemical (dye sensitised TiO{sub}2 or Gratzel) cells, plays a crucial role in achieving good conversion efficiency. The electrolyte, requires to permeate the highly porous TiO{sub}2 nanostructure, allowing all the dye coated nanoparticle surfaces to participate in the charge transfer reaction, whilst providing suitable energy levels to allow the regeneration of the dye, and sufficient ion transport to sustain the photocurrent output of the cell under full illumination [2]. A low viscosity liquid electrolyte based on an iodide-iodate redox couple in acetonitrile has been found to well matched to the energy levels of the dye and to meet the other requirements of the cell, and is used in the large majority of photoelectrochemical solar cells. The negatively charged redox species in these electrolytes are also thought to play a part in reducing undesirable recombination reactions of the injected electrons.