The 2010 Millennium Prize Laureate Michael Grätzel is the father of third generation dye-sensitized solar cells. Grätzel cells, which promise electricity-generating windows and low-cost solar panels, have just made their debut in consumer products. The technology often described as ‘artificial photosynthesis’ is a promising alternative to standard silicon photovoltaics. It is made of low-cost materials and does not need an elaborate apparatus to manufacture. Though DSC cells are still in relatively early stages of development, they show great promise as an inexpensive alternative to costly silicon solar cells and an attractive candidate for a new renewable energy source.
The key patent describing Grätzel’s invention was first filed as a GB patent with a priority date of 17th April 1990. The technology was published in Nature in 1991 and the first patents were granted in 1994. US5350644B1 was published on 27th Sept 1994 and has now been cited by over 70 other patents indicating the significance of this invention. However, it was not until 2009 that mass production of the solar cells began.
The opening sentence of the patent very simply states the essence of the invention: “The invention relates to new transition metal dyestuffs and to their use in photovoltaic cells. These dyes can be coated on titanium dioxide films rendering such devices effective in the conversion of visible light to electric energy”
The first claim reads as follows:
- A solar-light-responsive photovoltaic cell comprising a first electrode comprising
i) a light transmitting electrically conductive layer deposited on a glass plate or a transparent polymer sheet;
ii) at least one porous, high surface area titanium dioxide layer applied to said light transmitting electrically conductive layer;
iii) a dopant applied to at least the outermost titanium dioxide layer, optionally also to the second to the outermost and third to the outermost layer, said dopant being selected from a divalent metal ion, trivalent metal ion, and boron; and
iv) a photosensitizer applied to the dopant-containing TiO2 layer, said photosensitizer being attached to the TiO2 layer by means of interlocking groups, said interlocking groups being selected from carboxylate groups, cyano groups, phosphate groups and chelating groups with conducting character selected from oximes, dioximes, hydroxy quinolines, salicylates, and α-keto-enolates.