International Business Machines Corporation

Gilbert C Collins

Colin Leonard Bird

David J Schiffrin

John A Barltrop

The lifetime of a metal diphthalocyanine electrochromic display can be substantially extended by employing a predominantly non-aqueous low hydroxyl ion electrolyte. A preferred electrolyte solvent is ethylene glycol and preferred conductivity salts are tetraethyl ammonium fluoride and sodium chloride. In the case of sodium chloride, conductivity is improved by the addition of up to 25% water to the electrolyte.

Metal diphthalocyanine electrochromic displays and electrolytes therefor

An electrolyte for an electrochromic display of the kind in which a persistent colored species of an electrochromic substance in solution is deposited onto a display electrode upon the passage of current therethrough is disclosed. The electrolyte comprises an aqueous solution of a di-alkyl bipyridinium salt and a non-polymeric aliphatic alcohol in which either: (a) both alkyl groups of the bipyridinium salt have an odd number of carbon atoms and the alcohol has an even number of carbon atoms; or (b) both alkyl groups of the bipyridinium salt have an even number of carbon atoms and the alcohol has an odd number of carbon atoms. The presence of an alcohol in the electrolyte inhibits recrystallization (spotting) and non-erasure of the display electrodes. A particularly effective alcohol for 1,1' di-heptyl 4,4' bipyridinium dibromide, which has a severe lifetime problem, is n-hexanol.

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Southampton, United Kingdom

Gilbert C Collins