Bifacial solar cells with back surface reflector

1 . A method of fabricating a bifacial solar cell (BSC), the method comprising the steps of:

depositing a dopant of a first conductivity type onto a back surface of a silicon substrate of said first conductivity type to form a back surface doped region;

depositing a back surface dielectric over said back surface doped region;

forming an active area of a second conductivity type on a front surface of said silicon substrate, said forming step including a thermal diffusing step, wherein said method includes a single thermal diffusing step;

etching said active area;

depositing a front surface passivation and anti-reflection (AR) dielectric layer onto said active area;

applying a back surface contact grid;

applying a front surface contact grid;

firing said back surface contact grid;

firing said front surface contact grid;

depositing a layer of amorphous silicon onto said back surface contact grid and said back surface dielectric, wherein said layer of amorphous silicon is doped with a second dopant of said first conductivity type;

depositing a layer of metal over said layer of amorphous silicon; and

isolating said active area.

2 . The method of claim 1 , wherein said step of applying said back surface contact grid further comprises the step of screen printing said back surface contact grid, and wherein said step of applying said front surface contact grid further comprises the step of screen printing said front surface contact grid.

3 . The method of claim 1 , further comprising the step of depositing a conductive interface layer between said layer of amorphous silicon and said layer of metal, wherein said conductive interface layer depositing step is performed prior to said metal layer depositing step.

4 . A method of fabricating a bifacial solar cell, the method comprising the steps of:

depositing a boron doped layer on a back surface of a p-type silicon substrate;

depositing a back surface dielectric onto said boron doped layer;

diffusing phosphorous onto a front surface of said silicon substrate to form an n + layer and a front surface junction;

removing a phosphor-silicate glass (PSG) formed during said phosphorous diffusing step;

depositing a front surface passivation and anti-reflection (AR) dielectric layer onto said n + layer;

applying a back surface contact grid;

applying a front surface contact grid;

firing said back surface contact grid;

firing said front surface contact grid;

depositing a boron doped layer of amorphous silicon onto said back surface contact grid and said back surface dielectric;

depositing a metal layer onto said boron doped layer of amorphous silicon; and

isolating said front surface junction.

5 . The method of claim 4 , wherein said step of applying said back surface contact grid further comprises the step of screen printing said back surface contact grid, and wherein said step of applying said front surface contact grid further comprises the step of screen printing said front surface contact grid.

6 . The method of claim 4 , wherein said step of isolating said front surface junction is performed using a laser scriber.

7 . The method of claim 4 , further comprising the step of depositing a conductive interface layer between said boron doped layer of amorphous silicon and said layer of metal, wherein said conductive interface layer depositing step is performed prior to said metal layer depositing step.

8 . The method of claim 7 , wherein said conductive interface layer is comprised of a material selected from the group consisting of indium tin oxide and aluminum-doped zinc oxide.

9 . The method of claim 4 , wherein said steps of firing said back and front surface contact grids are performed simultaneously.

10 . The method of claim 4 , wherein said step of firing said back surface contact grid is performed prior to said step of applying said front surface contact grid.

11 . The method of claim 4 , wherein said boron doped layer depositing step further comprises the step of depositing a boron doped silicon dioxide layer using chemical vapor deposition.

12 . The method of claim 4 , wherein said boron doped layer depositing step further comprises the step of depositing a boron doped silicon layer using chemical vapor deposition.

13 . The method of claim 4 , wherein said boron doped layer depositing step further comprises the step of depositing a boron doped amorphous silicon layer using plasma enhanced chemical vapor deposition.

14 . The method of claim 4 , wherein said boron doped layer depositing step further comprises the step of spraying a boric acid solution onto said back surface of said silicon substrate.

15 . The method of claim 4 , wherein said boron doped layer depositing step further comprises the step of spraying a boron doped spin-on glass onto said back surface of said silicon substrate.

16 . The method of claim 4 , wherein said PSG removing step further comprises the step of etching said front surface with a hydrofluoric etch.

17 . The method of claim 4 , further comprising the step of selecting said back surface dielectric and said front surface passivation and AR dielectric from the group consisting of silicon nitrides, silicon dioxides and silicon oxynitrides.

18 . The method of claim 4 , wherein said phosphorous diffusing step is performed at a temperature of approximately 850° C. for a duration of approximately 10 to 20 minutes.

19 . The method of claim 4 , wherein said back surface dielectric depositing step is performed after said step of applying said back surface contact grid.

20 . A bifacial solar cell, comprising:

a silicon substrate of a first conductivity type with a front surface and a back surface;

a doped region of said first conductivity type located on said back surface of said silicon substrate;

a dielectric layer deposited on said doped region;

an active region of a second conductivity type located on said front surface of said silicon substrate;

a passivation and AR dielectric layer deposited on said active region;

a first contact grid applied to said dielectric layer, said first contact grid comprised of a first metal, wherein after a firing step said first contact grid is alloyed through said dielectric layer to said doped region located on said back surface of said silicon substrate;

a second contact grid applied to said passivation and AR dielectric layer, said second contact grid comprised of a second metal, wherein after said firing step said second contact grid is alloyed through said passivation and AR dielectric layer to said active region;

a amorphous silicon layer doped with a dopant of said first conductivity type, said amorphous silicon layer deposited on said first contact grid and said dielectric layer; and

a blanket layer deposited on said amorphous silicon layer, said blanket layer comprised of a third metal.

21 . The bifacial solar cell of claim 20 , further comprising a groove on said front surface of said silicon substrate, said groove isolating a front junction formed by said active region and said silicon substrate.

22 . The bifacial solar cell of claim 20 , further comprising a conductive interface layer interposed between said amorphous silicon layer and said blanket layer.

23 . The bifacial solar cell of claim 22 , wherein said conductive interface layer is selected from the group of materials consisting of indium tin oxide and aluminum doped zinc oxide.

24 . The bifacial solar cell of claim 20 , wherein said silicon substrate is comprised of a p-type silicon, said active region is comprised of n + material resulting from a phosphorous diffusion step, and said doped region and said amorphous silicon layer further comprise a boron dopant.

25 . The bifacial solar cell of claim 24 , wherein said dielectric layer and wherein said passivation and AR dielectric layer are each comprised of a material selected from the group consisting of silicon nitrides, silicon dioxides and silicon oxynitrides.

26 . The bifacial solar cell of claim 20 , wherein said silicon substrate is comprised of an n-type silicon, said active region is comprised of p + material resulting from a boron diffusion step, and said doped region and said amorphous silicon layer further comprise a phosphorous dopant.

27 . A method of fabricating a bifacial solar cell (BSC), the method comprising the steps of:

forming an active area of a second conductivity type on a front surface of a silicon substrate of a first conductivity type, said forming step including a thermal diffusing step;

etching said front surface of said silicon substrate;

depositing a front surface passivation and anti-reflection (AR) dielectric layer onto said active area and a back surface dielectric layer onto said back surface of said silicon substrate;

applying a back surface contact grid;

applying a front surface contact grid;

firing said back surface contact grid;

firing said front surface contact grid;

depositing a layer of amorphous silicon onto said back surface contact grid and said back surface dielectric layer, wherein said layer of amorphous silicon is doped with a dopant of said first conductivity type; and

depositing a layer of metal over said layer of amorphous silicon.

28 . The method of claim 27 , wherein said step of applying said back surface contact grid further comprises the step of screen printing said back surface contact grid, and wherein said step of applying said front surface contact grid further comprises the step of screen printing said front surface contact grid.

29 . The method of claim 27 , further comprising the step of depositing a conductive interface layer between said layer of amorphous silicon and said layer of metal, wherein said conductive interface layer depositing step is performed prior to said metal layer depositing step.

30 . The method of claim 27 , further comprising the step of removing a back surface junction formed on a back surface of said silicon substrate during said active area forming step.

31 . A method of fabricating a bifacial solar cell, the method comprising the steps of:

diffusing phosphorous onto a front surface of a silicon substrate to form an n + layer and a front surface junction and onto a back surface of said silicon to form a back surface junction;

removing a phosphor-silicate glass (PSG) formed during said phosphorous diffusing step;

depositing a front surface passivation and anti-reflection (AR) dielectric layer onto said n + layer and a back surface dielectric layer onto said back surface of said silicon substrate;

applying a back surface contact grid;

applying a front surface contact grid;

firing said back surface contact grid;

firing said front surface contact grid; and

depositing a metal layer onto said back surface contact grid and said back surface dielectric.

32 . The method of claim 31 , wherein said step of applying said back surface contact grid further comprises the step of screen printing said back surface contact grid, and wherein said step of applying said front surface contact grid further comprises the step of screen printing said front surface contact grid.

33 . The method of claim 31 , wherein said steps of firing said back and front surface contact grids are performed simultaneously.

34 . The method of claim 31 , wherein said step of firing said back surface contact grid is performed prior to said step of applying said front surface contact grid.

35 . The method of claim 31 , further comprising the steps of removing said back surface junction and isolating said front surface junction.

36 . The method of claim 35 , wherein said back surface junction removing step further comprises the step of etching said back surface.

37 . The method of claim 35 , wherein said step of applying said back surface contact grid is performed after said back surface junction removing step and before said back surface dielectric layer depositing step.

38 . The method of claim 35 , further comprising the step of applying a back surface metal grid onto said back surface of said silicon substrate, wherein said back surface metal grid applying step is performed after said back surface junction removing step and before said back surface dielectric layer depositing step, and wherein the method of claim 31 further comprises the step of aligning said back surface contact grid with said back surface metal grid.

39 . The method of claim 38 , wherein said back surface metal grid applying step further comprises the steps of applying a shadow mask to said back surface of said silicon substrate and depositing said back surface metal grid onto said back surface of said silicon substrate.

40 . The method of claim 38 , wherein said back surface metal grid applying step further comprises the step of screen printing said back surface metal grid onto said back surface of said silicon substrate.

41 . The method of claim 38 , wherein said step of firing said back surface contact grid is performed prior to said step of applying said front surface contact grid.

42 . The method of claim 31 , wherein said PSG removing step further comprises the step of etching said front surface with a hydrofluoric etch.

43 . A method of fabricating a bifacial solar cell (BSC), the method comprising the steps of:

depositing a back surface dielectric layer onto a back surface of a silicon substrate of a first conductivity type;

forming an active area of a second conductivity type on a front surface of said silicon substrate, said forming step including a thermal diffusing step;

etching said front surface of said silicon substrate;

depositing a front surface passivation and anti-reflection (AR) dielectric layer onto said active area;

applying a back surface contact grid;

applying a front surface contact grid;

firing said back surface contact grid;

firing said front surface contact grid;

depositing a layer of amorphous silicon onto said back surface contact grid and said back surface dielectric layer, wherein said layer of amorphous silicon is doped with a dopant of said first conductivity type; and

depositing a layer of metal over said layer of amorphous silicon; and

isolating said front surface junction.

44 . The method of claim 43 , wherein said step of applying said back surface contact grid further comprises the step of screen printing said back surface contact grid, and wherein said step of applying said front surface contact grid further comprises the step of screen printing said front surface contact grid.

45 . The method of claim 43 , wherein said step of isolating said front surface junction is performed using a laser scriber.

46 . The method of claim 43 , further comprising the step of depositing a conductive interface layer between said layer of amorphous silicon and said layer of metal, wherein said conductive interface layer depositing step is performed prior to said metal layer depositing step.

47 . A method of fabricating a bifacial solar cell, the method comprising the steps of:

depositing a dielectric layer onto a back surface of a silicon substrate;

diffusing phosphorous onto a front surface of said silicon substrate to form an n + layer and a front surface junction;

removing a phosphor-silicate glass (PSG) formed during said phosphorous diffusing step;

depositing a front surface passivation and anti-reflection (AR) dielectric layer onto said n + layer;

applying a back surface contact grid;

applying a front surface contact grid;

firing said back surface contact grid;

firing said front surface contact grid;

depositing a boron doped layer of amorphous silicon onto said back surface contact grid and said back surface dielectric; and

depositing a metal layer onto said boron doped layer of amorphous silicon; and

isolating said front surface junction.

48 . The method of claim 47 , wherein said step of applying said back surface contact grid further comprises the step of screen printing said back surface contact grid, and wherein said step of applying said front surface contact grid further comprises the step of screen printing said front surface contact grid.

49 . The method of claim 47 , wherein said step of isolating said front surface junction is performed using a laser scriber.

50 . The method of claim 47 , further comprising the step of depositing a conductive interface layer between said boron doped layer of amorphous silicon and said layer of metal, wherein said conductive interface layer depositing step is performed prior to said metal layer depositing step.

51 . The method of claim 50 , wherein said conductive interface layer is comprised of a material selected from the group consisting of indium tin oxide and aluminum-doped zinc oxide.

52 . The method of claim 47 , wherein said steps of firing said back and front surface contact grids are performed simultaneously.

53 . The method of claim 47 , wherein said step of firing said back surface contact grid is performed prior to said step of applying said front surface contact grid.

54 . The method of claim 47 , wherein said PSG removing step further comprises the step of etching said front surface with a hydrofluoric etch.

55 . A bifacial solar cell, comprising:

a silicon substrate of a first conductivity type with a front surface and a back surface;

a first dielectric layer deposited on said back surface of said silicon substrate;

an active region of a second conductivity type located on at least a portion of said front surface of said silicon substrate;

a second dielectric layer deposited on said active region;

a first contact grid applied to said first dielectric layer, said first contact grid comprised of a first metal, wherein after a firing step said first contact grid is alloyed through said first dielectric layer to said back surface of said silicon substrate;

a amorphous silicon layer doped with a dopant of said first conductivity type, said amorphous silicon layer deposited on said first contact grid and said first dielectric layer; and

a blanket layer deposited on said amorphous silicon layer, said blanket layer comprised of a third metal.

56 . The bifacial solar cell of claim 55 , further comprising a conductive interface layer interposed between said amorphous silicon layer and said blanket layer.

57 . The bifacial solar cell of claim 56 , wherein said conductive interface layer is selected from the group of materials consisting of indium tin oxide and aluminum doped zinc oxide.

58 . The bifacial solar cell of claim 55 , wherein said silicon substrate is comprised of a p-type silicon, said active region is comprised of n + material resulting from a phosphorous diffusion step, and said amorphous silicon layer further comprises a boron dopant.

59 . The bifacial solar cell of claim 55 , further comprising a grid pattern of a third metal deposited directly on said back surface of said silicon substrate and interposed between said back surface of said silicon substrate and said first dielectric layer, wherein said first contact grid is registered to said grid pattern, and wherein after said firing step said first contact grid is alloyed through said first dielectric layer to said grid pattern of said third metal.

60 . The bifacial solar cell of claim 55 , wherein said first contact grid is applied directly to said back surface of said silicon substrate and prior to said first dielectric layer.

61 . The bifacial solar cell of claim 55 , further comprising a groove on said front surface of said silicon substrate, said groove isolating a front junction formed by said active region and said silicon substrate.

62 . The bifacial solar cell of claim 55 , wherein said silicon substrate is comprised of an n-type silicon, said active region is comprised of p + material resulting from a boron diffusion step, and said amorphous silicon layer further comprises a phosphorous dopant.