Additives to silane for thin film silicon photovoltaic devices

1. A method of deposition for a solar grade amorphous silicon film (αSi:H) as a photoconductive film on a substrate, using

Silane;

hydrogen; and

at least one additive selected from the group consisting of:

(a) higher order straight chain silanes, comprising; disilane Si 2 H 6 , trisilane Si 3 H 8 , tetrasilane Si 4 H 10 , pentasilane Si 5 H 12 ,hexasilane Si 6 H 14 , heptasilane Si 7 H 16 , octasilane Si 8 H 18 , nonasilane Si 9 H 20 , decasilane Si 10 H 22 and mixtures thereof;

(b) higher order branched silanes, comprising; 2-silyl-trisilane SiH 3 —Si(H)(SiH 3 )—SiH 3 , 2,2-disilyl-trisilane SiH 3 —Si(SiH 3 ) 2 —SiH 3 , 2-silyl-tetrasilane SiH 3 —Si(H)(SiH 3 )—SiH 2 —SiH 3 , 2,3-disilyltetrasilane SiH 3 —SiH(SiH 3 )—SiH(SiH 3 )—SiH 3 , 2,2-disilyltetrasilane SiH 3 —Si(SiH 3 ) 2 —SiH 2 —SiH 3 , 3-silylpentasilane SiH 3 —SiH 2 —SiH(SiH 3 )—SiH 2 —SiH 3 , 2-silylpentasilane SiH 3 —SiH(SiH 3 )—SiH 2 —SiH 2 —SiH 3 , 2,3-disilylpentasilane SiH 3 —SiH(SiH 3 )—SiH(SiH 3 )—SiH 2 —SiH 3 , 2,4disilylpentasilane SiH 3 —SiH(SiH 3 )—SiH 2 —SiH(SiH 3 )—SiH 3 , 2-silylhexasilane SiH 3 —SiH(SiH 3 )—(SiH 2 ) 3 SiH 3 , 3-silylhexasilane SiH 3 —SiH 2 —SiH(SiH 3 )—(SiH 2 ) 2 SiH 3 , 2,2disilylpentasilane SiH 3 —Si(SiH 3 ) 2 —(SiH 2 ) 2 —SiH 3 , 3,3-disilylpentasilane SiH 3 —SiH 2 Si (SiH 3 ) 2 —SiH 2 —SiH 3 , 2,2,3-trisilyltetrasilane SiH 3 —Si(SiH 3 ) 2 —SiH(SiH 3 )—SiH 3 , 2silylheptasilane SiH 3 —SiH(SiH 3 )—(SiH 2 ) 4 —SiH 3 , 3-silylheptasilane SiH 3 —SiH 2 —SiH(SiH 3 )—(SiH 2 ) 3 —SiH 3 , 4-silylheptasilane SiH 3 —(SiH 2 ) 2 —SiH(SiH 3 )—(SiH 2 ) 2 —SiH 3 , 2,2-disilylhexasilane SiH 3 —Si(SiH 3 ) 2 —(SiH 2 ) 3 —SiH 3 , 2,3-disilylhexasilane SiH 3 —SiH(SiH 3 ) —SiH(SiH 3 )—(SiH 2 ) 2 —SiH 3 , 2,4-disilylhexasilane SiH 3 —SiH(SiH 3 )—SiH 2 —SiH(SiH 3 )—SiH 2 —SiH 3 , 2,5-disilylhexasilane SiH 3 —SiH(SiH 3 )—(SiH 2 ) 2 —SiH(SiH 3 ) SiH 3 , 3,3-disilylhexasilane SiH 3 —SiH 2 —Si(SiH 3 ) 2 —(SiH 2 ) 2 —SiH 3 , 3,4disilylhexasilane SiH 3 —SiH 2 —SiH(SiH 3 )—SiH(SiH 3 )—SiH 2 —SiH 3 , 2,2,3trisilylpentasilane SiH 3 —Si(SiH 3 ) 2 —SiH(SiH 3 )—SiH 2 —SiH 3 , 2,2,4-trisilylpentasilane SiH 3 —Si(SiH 3 ) 2 —SiH 2 —SiH(SiH 3 )—SiH 3 , 2,3,3-trisilylpentasilane SiH 3 —SiH(SiH 3 )—Si(SiH 3 ) 2 —SiH 2 —SiH 3 , 2,3,4-trisilylpentasilane SiH 3 —SiH(SiH 3 )—SiH(SiH 3 )—SiH(SiH 3 )—SiH 3 , 2,2,3,3-tetrasilyltetrasilane SiH 3 —Si(SiH 3 ) 2 —Si(SiH 3 ) 2 —SiH 3 and mixtures thereof;

(c) cyclic silanes, selected from the group consisting of; cyclotrisilane Si 3 H 6 cyclotetrasilane Si 4 H 8 , cyclopentasilane Si 5 H 10 , cyclohexasilane Si 6 H 10 , and mixtures thereof;

(d) silyl substituted cyclic silanes, selected from the group consisting of; silyl cyclotetrasilane SiH3—Si 4 H 7 , 1,2-disilylcyclopentasilane (SiH 3 ) 2 —Si 5 H 8 , silyl cyclohexasilane SiH 3 —Si 6 H 11 , 1,3-disilylcyclohexasilane (SiH 3 ) 2 —Si 6 H 10 , and mixtures thereof;

(e) silyl substituted silanes, selected from the group consisting of; 2-tetrasilane SiH 3 —SiH═SiH—SiH 3 , 2,3-disilyltetrasil-2-ene SiH 3 —Si(SiH 3 )═Si(SiH 3 )—SiH 3 , 2,3disilylpentasil-2-ene SiH 3 —Si(SiH 3 )═Si(SiH 3 )—SiH 2 —SiH 3 , 2,5-disilylhexasil-2-ene SiH 3 —Si(SiH 3 )═SiH—SiH2—SiH(SiH 3 )—SiH 3 , 2,3,4-trisilylhexasil-2-ene SiH 3 —Si(SiH 3 )═Si(SiH 3 )—SiH(SiH 3 )—SiH 2 —SiH 3 , and mixtures thereof;

(f) halogen substituted silanes, including; 1 , 1 -dichlordisilane SiHCl 2 SiH 3 , 1,1,1,2-tetrafluorodislane SiF 3 —SiH 2 F, 1,2-dichloro-1,2-difluorotetrasilane SiHCIF—SiCIF—SiH 2 —SiH 3 , 1,1,1-trichlorotrisilane SiCl 3 —SiH 2 —SiH 3 , 1,1-difluoro1,2,2-trichlorosilane SiF 2 Cl—SiCl 2 —SiH 3 , chloropentasilane SiH 2 Cl—(SiH 2 ) 3 —SiH 3 , and other compounds of the general formula Si w H 2w+2−z X z where X ═F, Cl, Br, 1; w can be 1 to 20 and z can be 1 to 2w+2; 2-chlorotetrasil-2-ene SiH 3 —SiCl═SiH—SiH 3 , 1,1-dichloro-2-fluoropentasil-2-ene SiHCl 2 —SiF═SiH 2 —SiH 2 —SiH 3 , 2,3-dichlorotetrasil-2-ene SiH 3 —SiCl═SiCl—SiH 3 , and other compounds of the general formula Si w H 2w− X′ z where X′═F, Cl, Br, I; and, w can be 2 to 20 and z can be 1 to 2w; and mixtures thereof; and

(g) halogen substituted cyclic silanes, selected from the group consisting of; chlorocyclopentasilane Si 5 H 9 Cl, dodecachlorocyclohexasilane Si 6 Cl 12 , 1chloro-1fluorocyclopentasilane Si 5 H 8 FCl, and mixtures thereof;

wherein the silane used is at 5 to 10%, and the at least one additive used is at 0.01 to 5%, and the rest is hydrogen .

2. The method of deposition for the solar grade amorphous silicon film (αSi:H) of claim 1 , wherein the deposition is performed at a substrate temperature of 25°-500° C., and pressure of 0.01 torr to 15 torr.

3. The method of deposition for the solar grade amorphous silicon film (αSi:H) of claim 2 , wherein the substrate temperature is at 150°-250° C.

4. The method of deposition for the solar grade amorphous silicon film (αSi:H) of claim 1 , wherein the deposition is a process selected from the group consisting of Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), Low Pressure Chemical Vapor Deposition (LPCVD), Hot Wire Chemical Vapor Deposition (HWCVD), Initiated Chemical Vapor Deposition (ICVD) and Sub Atmospheric Chemical Vapor Deposition (SA-CVD).

5. The method of deposition for the solar grade amorphous silicon film (αSi:H) of claim 1 , wherein the deposition is a plasma enhanced chemical vapor deposition at a plasma power density ranging from 0.19 -1.6W/cm 2 and a plasma frequency ranging from 13.56 to 40.68 MHz.

6. The method of deposition for the solar grade amorphous silicon film (αSi:H) of claim 5 having a deposition rate ranging from 10 - 200 Å/sec.

7. The method of deposition for the solar grade amorphous silicon film (αSi:H) of claim 5 , wherein a deposited film provides a single junction solar cell having efficiencies of 5 -15%; and a tandem junction solar cell having efficiencies of 7 - 20%.

8. A method of deposition for a solar grade amorphous silicon film (αSi:H) or a microcrystalline silicon film (μCSi:H) having high microcrystalline fraction as a photoconductive film on a substrate, using

Silane;

hydrogen; and

at least one additive selected from the group consisting of:

(a) halogen substituted higher order silanes, including; 1,1-dichlordisilane SiHCl 2 SiH 3 , 1,1,1,2-tetrafluorodislane SiF 3 —SiH 2 F, 1,2-dichloro-1,2difluorotetrasilane SiHCIF—SiCIF—SiH 2 —SiH 3 , 1,1,1-trichlorotrisilane SiCI 3 —SiH 2 —SiH 3 , 1,1-difluoro-1,2,2-trichlorosilane SiF 2 Cl—SiCl 2 —SiH 3 , chloropentasilane SiH 2 Cl—(SiH 2 ) 3 —SiH 3 , and other compounds of the general formula Si w H 2w+2−z X z where X ═F, Cl, Br, I; w can be 1 to 20 and z can be 1 to 2w+2; 2chlorotetrasil-2-ene SiH 3 —SiCl═SiH—SiH 3 , 1,1-dichloro-2-fluoropentasil-2-ene SiHCl 2 —SiF═SiH 2 —SiH 2 —SiH 3 , 2,3-dichlorotetrasil-2-ene SiH 3 —SiCl═SiCl—SiH 3 , and other compounds of the general formula Si w H 2w−z X′ z where X′═F, Cl, Br, I; and, w can be 2 to 20 and z can be 1 to 2w; and mixtures thereof; and

(b) halogen substituted cyclic higher order silanes, selected from the group consisting of; chlorocyclopentasilane Si 5 H 9 Cl, dodecachlorocyclohexasilane Si 6 Cl 12 , 1-chloro-1fluorocyclopentasilane Si 5 H 8 FCl, and mixtures thereof.

9. The method of deposition for the solar grade amorphous silicon film (αSi:H) or the microcrystalline silicon film (μCSi:H) having high microcrystalline fraction of claim 8 , wherein the silane used is at 5 to 10%, and the at least one additive used is at 0.01 to 5%, and the rest is hydrogen.

10. The method of deposition for the solar grade amorphous silicon film (αSi:H) or the microcrystalline silicon film (μCSi:H) having high microcrystalline fraction of claim 8 , wherein the deposition is a process selected from the group consisting of Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), Low Pressure Chemical Vapor Deposition (LPCVD), Hot Wire Chemical Vapor Deposition (HWCVD), Initiated Chemical Vapor Deposition (ICVD) and Sub Atmospheric Chemical Vapor Deposition (SA-CVD).

11. The method of deposition for the solar grade amorphous silicon film (αSi:H) or the microcrystalline silicon film (μCSi:H) having high microcrystalline fraction of claim 8 , wherein the deposition is a plasma enhanced chemical vapor deposition at a plasma power density ranging from 0.19 -1.6 W/cm 2 and a plasma frequency ranging from 13.56 to 40.68 MHz.

12. The method of deposition for the solar grade amorphous silicon film (αSi:H) or the microcrystalline silicon film (μCSi:H) having high microcrystalline fraction of claim 11 , having a deposition rate of 10 - 200Å/sec for amorphous silicon film (αSi:H) and 10 - 100 Å/sec for microcrystalline silicon film (μCSi:H).

13. The method of deposition for the solar grade amorphous silicon film (αSi:H) or the microcrystalline silicon film (μCSi:H) having high microcrystalline fraction of claim 11 , wherein the deposited amorphous silicon film (αSi:H) provides a single junction solar cell having efficiencies of 5 -15%; and the deposited amorphous silicon film (αSi:H) or microcrystalline silicon film (μCSi:H) provides a tandem junction solar cell having efficiencies of 7 - 20%.