Devices and methods for photoelectrochemical water splitting

Abstract

when the photoelectrochemical electrode is configured to be in contact with water.

What is claimed is: 
     
         1 . A photoelectrochemical electrode comprising:
 an absorber layer comprising a quantum well, wherein:   the photoelectrochemical electrode is configured to perform a first reaction defined as,
   4H + +4e −   2H 2 , 
   or a second reaction defined as,
   2H 2 O O 2 +4H + +4e − , 
   when the photoelectrochemical electrode is configured to be in contact with water.   
     
     
         2 . The photoelectrochemical electrode of  claim 1 , wherein:
 the quantum well comprises, in order:
 a first barrier layer having a first bandgap; 
 a well layer having a second bandgap; and 
 a second barrier having a third bandgap, wherein; 
   the second bandgap is less than the first bandgap and the third bandgap.   
     
     
         3 . The photoelectrochemical electrode of  claim 2 , wherein:
 the first bandgap and the third bandgap are between about 1.4 eV and about 1.66 eV, inclusively, and   the second bandgap is between about 1.13 and about 1.4 eV, inclusively.   
     
     
         4 . The photoelectrochemical electrode of  claim 3 , wherein:
 the first barrier layer and the second barrier both comprise GaAs 1-y P y , and   y is between about 0.0 and about 0.2, inclusively.   
     
     
         5 . The photoelectrochemical electrode of  claim 3 , wherein:
 the well layer comprises Ga 1-x In x P, and   x is between about 00.0 and about 0.2, inclusively.   
     
     
         6 . The photoelectrochemical electrode of  claim 2 , wherein:
 the first barrier layer and the second barrier layer have a thickness between about 1 nm and about 50 nm, and   the well layer has a thickness between about 1 nm and about 20 nm.   
     
     
         7 . The photoelectrochemical electrode of  claim 1 , wherein the absorber layer comprises between 1 and 100 quantum wells. 
     
     
         8 . The photoelectrochemical electrode of  claim 1 , further comprising:
 a substrate layer; and   a reflecting layer, wherein:   the reflecting layer is positioned between the substrate and the absorber layer, and   the reflecting layer is a Bragg reflector.   
     
     
         9 . The photoelectrochemical electrode of  claim 8 , wherein the substrate is lattice-matched to the quantum well. 
     
     
         10 . The photoelectrochemical electrode of  claim 8 , wherein the substrate is lattice-mismatched to the quantum well. 
     
     
         11 . The photoelectrochemical electrode of  claim 8 , wherein:
 the Bragg reflector comprises:
 a first layer having a first index of refraction; and 
 a second layer having a second index of refraction, wherein: 
   the first index of refraction is different than the second index of refraction.   
     
     
         12 . The photoelectrochemical electrode of  claim 1 , wherein both the first index of refraction and the second index of refraction are between 2.5 and 4.0, inclusively. 
     
     
         13 . The photoelectrochemical electrode of  claim 12 , wherein:
 the first index of refraction is about 3.5,   and the second index of refraction is about 3.0.   
     
     
         14 . The photoelectrochemical electrode of  claim 13 , wherein:
 the first layer comprises GaAs, and   the second layer comprises AlAs.   
     
     
         15 . The photoelectrochemical electrode of  claim 8 , wherein:
 the absorber layer further comprises:
 a first doped layer, and 
 a second doped layer, wherein: 
   the quantum well is positioned between the first doped layer and the second doped layer,   the second doped layer is positioned between the substrate and the second doped layer, and   the second doped layer is the opposite doping of the first doped layer.   
     
     
         16 . The photoelectrochemical electrode of  claim 15 , wherein:
 the first doped layer is p-type or n-type,   the second doped layer is p-type or n-type, and   the doping type of the second doped layer is the opposite of the doping type of the first doped layer.   
     
     
         17 . The photoelectrochemical electrode of  claim 16 , wherein:
 the first doped layer and the second doped layer each have a bandgap between about 1.0 eV and about 1.5 eV, inclusively.   
     
     
         18 . The photoelectrochemical electrode of  claim 17 , wherein:
 both the first doped layer and the second doped layer comprise Al x Ga y In z As v P w N t Sb u ,   x is between 0.0 and 1.0, y is between 0.0 and 1.0, z is between 0.0 and 1.0, v is between 0.0 and 1.0, w is between 0.0 and 1.0, t is between 0.0 and 1.0, u is between 0.0 and 1.0, and x+y+z=u+t+v+w=1.0.   
     
     
         19 . The photoelectrochemical electrode of  claim 18 , wherein at least one of the first doped layer or the second doped layer comprises GaAs. 
     
     
         20 . The photoelectrochemical electrode of  claim 15 , further comprising:
 a second absorber layer, wherein:   the absorber layer having the quantum well is positioned between the reflecting layer and the second absorber layer.