Substantial Lifetime Enhancement of Si-Based Photoanodes Enabled by Amorphous TiO2 Coating with Improved Stoichiometry

Abstract

A post-ALD in-situ water treatment procedure is used to remove the ligand residues in amorphous TiO 2 films coated on photoanode material to improve the film stoichiometry without introducing any additional crystallization. The processed amorphous TiO 2 film showed drastically improved chemical stability, and thereby substantially elongated the lifetime of silicon-based photoanodes in alkaline electrolyte.

What we claim is: 
     
         1 . A method of removing precursor ligands and byproducts in a photoelectrode, the method comprising:
 (a) performing an atomic layer deposition of an oxide onto a photoanode material including the steps of:
 pulsing oxygen precursors onto a photoanode material surface; 
 purging the photoanode material surface with an inert gas; 
 pulsing metal precursors onto the photoanode material surface; and 
 purging the photoanode material surface with the inert gas 
   to deposit a thin film of oxide onto the photoanode material surface to produce a thin film matrix;   (b) performing a water treatment of the thin film matrix including the steps of:
 pulsing the oxygen precursors onto the thin film matrix; and 
 purging the thin film matrix with the inert gas; 
   to reduce a ratio of precursor ligand to oxide from the thin film matrix.   
     
     
         2 . The method of  claim 1  wherein the water treatment reduces the ratio of precursor ligand to oxide by at least 20%. 
     
     
         3 . The method of  claim 2  wherein the water treatment reduces the ratio of precursor ligand to oxide by at least 25%. 
     
     
         4 . The method of  claim 1  wherein the photoanode material is silicon. 
     
     
         5 . The method of  claim 1  wherein the thin film of oxide is TiO 2 . 
     
     
         6 . The method of  claim 5  wherein the metal precursors are TiCl 4 . 
     
     
         7 . The method of  claim 6  wherein the precursor ligands are Cl ligands. 
     
     
         8 . The method of  claim 7  wherein the inert gas is N 2  or Ar. 
     
     
         9 . The method of  claim 1  further comprising sputtering nickel (Ni) onto the thin film matrix. 
     
     
         10 . The method of  claim 1  where the step of water pulsing has a duration of at least 2 hours. 
     
     
         11 . The method of  claim 10  wherein the step of water pulsing onto the thin film matrix is pulsing a water pulse that is at least 0.5 second and the water pulse is repeated. 
     
     
         12 . The method of  claim 1  wherein the step of inert gas purging has a duration of at least 5 hours. 
     
     
         13 . The method of  claim 12  where the step of inert gas purging onto the thin film matrix is purging with an inert gas at least 0.5 second and the insert gas purging is repeated. 
     
     
         14 . The method of  claim 1  wherein the temperature of the atomic layer deposition is at less than or equal to 80 degrees Celsius. 
     
     
         15 . The method of  claim 1  wherein the temperature of the water treatment is at less than or equal to 80 degrees Celsius. 
     
     
         16 . The method of  claim 1  wherein the thin film of oxide has a thickness that is less than 15 nm. 
     
     
         17 . The method of  claim 1  wherein the thin film matrix has a thickness that is less than 40 nm. 
     
     
         18 . The method of  claim 1  wherein the atomic layer deposition and water treatment are performed in a vacuum. 
     
     
         19 . A photoelectrode comprising:
 a thin film of oxide deposited onto a photoanode material via atomic layer deposition using a metal precursor reacted with an oxygen precursor resulting in a precursor ligand;   wherein the precursor ligand to oxide ratio is less than 3%.   
     
     
         20 . The photoelectrode of  claim 19  wherein the photoanode material is silicon and the thin film of oxide is TiO 2 .