Method of optimizing the band edge positions of the conduction band and the valence band of a semiconductor material for use in photoactive devices

Abstract

The present invention relates to a semiconductor compound having the general formula A x B 1-x C y , to a method of optimizing positions of a conduction band and a valence band of a semiconductor material using said semiconductor compound, and to a photoactive device comprising said semiconductor compound.

1 . A method of optimizing positions of a conduction band and a valence band and/or the energy difference between a conduction band and a valence band of a semiconductor material in a semiconductor layer of a photoactive device, preferably a dye-sensitised solar cell having a dye in said semiconductor layer, and/or of optimizing an open circuit voltage of said device, preferably of said dye-sensitised solar cell, using a semiconductor compound having a formula A x B 1-x C y , wherein A and B are metals or metalloids, and wherein C is a non-metal or a metalloid, preferably selected from the group comprising C, N, O, P, S, Se, As, NO 2 , NO 3 , SO 3 , SO 4 , PO 4 , PO 3 , CO 3 , x is in the range of from 0.001 to 0.999 and y is in the range of from 0.1 to 10
 characterized in that   said semiconductor compound is synthesized starting from at least two precursor compounds, which are metal isopropoxides of the general formulae A u (iPrO) w  and B s (iPrO) t , wherein A and B are metals or metalloids selected from the group comprising Zr, Ti, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Sn, Nb, Zn, Ag, Pt, Ce, Ge, As, Ga, Si, Al, Cu, CuAl, CuNi, PbZr, SrTi, BaZr, SrCu 2 , and s, u, t and w are in the range of from 1 to 10, and (iPrO) is an isopropoxide-group.   
   
   
       2 . A method of optimizing positions of a conduction band and a valence band and/or the energy difference between a conduction band and a valence band of a semiconductor material in a semiconductor layer of a photoactive device, preferably a dye-sensitised solar cell having a dye in said semiconductor layer, and/or of optimizing an open circuit voltage of said device, preferably of said dye-sensitised solar cell, using a semiconductor compound having a formula A x B 1-x C y , wherein A and B are metals or metalloids, and wherein C is a non-metal or a metalloid, preferably selected from the group comprising C, N, O, P, S, Se, As, NO 2 , NO 3 , SO 3 , SO 4 , PO 4 , PO 3 , CO 3 , x is in the range of from 0.001 to 0.999 and y is in the range of from 0.1 to 10
 characterized in that   said semiconductor compound is synthesized starting from an oxide, AO m  and a nitrate, B(NO 3 ) q , A and B are metals or metalloids being selected from the group comprising Zr, Ti, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Sn, Nb, Zn, Ag, Pt, Ce, Ge, As, Ga, Si, Al, Cu, CuAl, CuNi, PbZr, SrTi, BaZr, SrCu 2 , and m and q being in the range of from 0.1 to 10, wherein said oxide and said nitrate have been reacted together, preferably by mixing them.   
   
   
       3 . The method according to  claim 1  or  2 , characterized in that said semiconductor compound has an upper edge of a valence band and a lower edge of a conduction band, wherein said upper edge of said valence band is between an upper edge of a valence band of a first semiconductor compound AC v  and an upper edge of a valence band of a second semiconductor compound BC z , and said lower edge of said conduction band of said semiconductor compound is between a lower edge of a conduction band of said first semiconductor compound AC v  and a lower edge of a conduction band of said second semiconductor compound BC z , wherein A and B are metals or metalloids, and wherein v and z are in the range of from 0.1 and 10, and wherein y in said semiconductor compound having the formula A x B 1-x C y  is y=(1−x)*z+x*v. 
   
   
       4 . The method according to any of the foregoing claims, wherein A and B are metals or metalloids selected from the group comprising Zr, Ti, Hf. V, Ta, Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Sn, Nb, Zn, Ag, Pt, Ce, Ge, As, Ga, Si, Al, Cu, CuAl, CuNi, PbZr, SrTi, BaZr, SrCu 2 . 
   
   
       5 . The method according to any of the foregoing claims, wherein C is O, said semiconductor compound thus being a mixed semiconductor oxide. 
   
   
       6 . The method according to  claim 1  or to any of  claims 3  to  5 , characterized in that said semiconductor compound is synthesized starting from three, four or more different precursor compounds, preferably metal isopropoxides as defined in  claim 1 . 
   
   
       7 . The method according to  claim 1  or to any of  claims 3  to  6 , wherein AC v  and BC z  are independently selected from the group comprising TiO 2 , SnO 2 , ZnO, Nb 2 O 5 , ZrO 2 , CeO 2 , WO 3 , Cr 2 O 3 , CrO 2 , CrO 3 , SiO 2 , Fe 2 O 3 , CuO, Al 2 O 3 , CuAlO 2 , SrTiO 3 , SrCu 2 O 2 , ZrTiO 4 . 
   
   
       8 . The method according to any of the foregoing claims, wherein the components A and B are present in said semiconductor compound in a ratio of from 1:1000 to 1000:1. 
   
   
       9 . The method according to  claim 2 , wherein, after said oxide and said nitrate have been reacted together, the resulting product is sintered, preferably at T>300° C. 
   
   
       10 . The method according to any of the foregoing claims characterized in that said semiconductor compound is synthesized by a process comprising the steps: mixing and reacting at least two precursor molecules, which are metal isopropoxides of the general formulae A u (iPrO) w  und B s (iPrO) t , wherein A and B are metals or metalloids selected from the group comprising Zr, Ti, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Sn, Nb, Zn, Ag, Pt, Ce, Ge, As, Ga, Si, Al, Cu, CuAl, CuNi, PbZr, SrTi, BaZr, SrCu 2  and s, u, t and w are in the range of from 0.1 to 10, and (iPrO) is an isopropoxide-group, preferably in a ratio in which said metals are desired to be present in the resulting compound, heating the resulting mixture, optionally in the presence of an acid, to a temperature between 50° C. and 300° C. for a period of time between 1 h and 20 h, filtering the product to obtain said semiconductor compound as a residue, or, alternatively, reacting an oxide, AO m , and a nitrate, B(NO 3 ) q , A and B being as defined before, and m and q being in the range of from 0.1 to 10, sintering the resulting product at a temperature >300° C., for a period of 10 minutes to 60 minutes, preferably at a temperature >400° C. for approximately 30 minutes. 
   
   
       11 . The method according to any of the foregoing claims, wherein said semiconductor compound is incorporated in said semiconductor layer of said device as semiconductor particles having an average diameter ≦1 μm, preferably ≦500 nm, more preferably ≦100 nm. 
   
   
       12 . The method according to  claim 11 , wherein said semiconductor particles have an outer shell made of the same and/or a further semiconductor compound, preferably a semiconductor oxide. 
   
   
       13 . The method according to any of  claims 11 - 12 , wherein said semiconductor particles have a shape selected from the group comprising rods, tubes, cylinders, cubes, parallelipeds, spheres, balls and ellipsoids. 
   
   
       14 . The method according to any of  claims 11 - 13 , wherein said semiconductor particles are a mixture of at least two kinds of particles differing in their average diameter or length, and/or differing in their composition. 
   
   
       15 . The method according to any of  claims 11 - 14 , wherein said semiconductor particles are a mixture of a first kind of particles and a second kind of particles, said first kind of particles having an average diameter or length in the range of from 1 nm to 30 nm, and said second kind of particles having an average diameter in the range of from 50 nm to 500 nm and/or length in the range of from 50 nm to 5 μm. 
   
   
       16 . The method according to any of  claims 11 - 15 , wherein said semiconductor particles are a mixture of a first kind of particles and a second kind of particles, said first kind of particles being made of a first semiconductor compound A x B 1-x C y  as defined in any of  claims 1 - 10 , with C being O, and said second kind of particles being made either of a second semiconductor compound A x B 1-x C y  as defined in any of  claims 1 - 10 , with C being O, or of any semiconductor oxide as defined in  claim 7  with respect to AC v  and/or BC z , and wherein said first semiconductor compound and said second semiconductor compound, may be the same or different. 
   
   
       17 . The method according to any of the foregoing claims, wherein said semiconductor layer has pores having a diameter in the range ≦1 μm, preferably in the range of from 1 nm to 500 nm, more preferably in the range of from 10 nm to 50 nm. 
   
   
       18 . The method according to any of the foregoing claims, wherein said semiconductor particles, during manufacturing of said device, preferably said dye-sensitised solar cell (DSSC), are applied via screen printing, doctor blading, drop casting, spin coating, inkjet printing, electrostatic layer-by-layer self-assembly, lift-off-process, mineralization process or anodic oxidation. 
   
   
       19 . The method according to any of the foregoing claims, characterized in that said semiconductor material is chosen such that it has an upper edge of a conduction band which is below or equal to a photo-excited state of said dye to allow electron injection from said dye into said conduction band upon photo-excitation of said dye, but which upper edge is between the upper edges of conduction bands of AC v  and BC z  as defined in any of  claims 3 - 10 . 
   
   
       20 . The method according to any of the foregoing claims, wherein said optimizing is a widening or narrowing of said energy difference between said conduction band and said valence band of said semiconductor material or is a shift in the position of a band gap between said conduction band and said valence band. 
   
   
       21 . The method according to any of the foregoing claims, wherein said optimizing is with respect to a photoexcited state of said dye, so as to enable electron injection from said photoexcited state into said conduction band of said semiconductor material, and is furthermore with respect to the redox potential of a redox couple present in said dye-sensitised solar cell (DSSC). 
   
   
       22 . A photoactive device, preferably a dye-sensitised solar cell (DSSC), comprising a semiconductor layer having as semiconductor material a semiconductor compound as defined in any of  claims 1 - 22 , preferably a mixed semiconductor oxide as defined in  claim 4 . 
   
   
       23 . The photoactive device according to  claim 22 , optimized by the method according to any of  claims 1 - 22 . 
   
   
       24 . The photoactive device according to  claim 23 , characterized in that it further comprises a dye in said semiconductor layer and further characterized in that the conduction band of said semiconductor material has been adjusted with respect to the excited state of said dye to ensure an efficient electron injection from the excited state of said dye to the conduction band of said semiconductor material, whilst making the upper edge of said conduction band of said semiconductor material to be as close as possible to said excited state of said dye. 
   
   
       25 . The photoactive device according to any of  claims 22 - 24 , characterized in that it is a device selected from the group comprising dye-sensitised solar cells, photoactive catalysts, self-cleaning windows, and water purification systems.