Abstract
In various embodiments, photovoltaic devices incorporate discontinuous passivation layers (i) disposed between a thin-film absorber layer and a partner layer, (ii) disposed between the partner layer and a front contact layer, and/or (iii) disposed between a back contact layer and the thin-film absorber layer.
Claims
1.-35. (canceled)
36. A photovoltaic device configured for top illumination by solar energy, the photovoltaic device comprising: a back contact layer comprising a conductive material; a discontinuous back reflector disposed over the back contact layer; a thin-film absorber layer disposed over an in electrical contact with the back contact layer, the thin-film absorber layer (i) having a doping polarity and (ii) comprising CdTe, chalcopyrite, or kesterite, wherein (a) the thin-film absorber layer makes direct electrical contact to the back contact layer through discontinuities in the discontinuous back reflector, and (b) the discontinuous back reflector is positioned to reflect solar energy passing through the thin-film absorber layer back through the thin-film absorber layer in a direction away from the back contact layer; a partner layer disposed over and in electrical contact with the thin-film absorber layer, the partner layer having a doping polarity opposite that of the thin-film absorber layer; a front contact layer disposed over and in electrical contact with the partner layer, the front contact layer comprising a second conductive material; and a discontinuous passivation layer disposed between the partner layer and the front contact layer, the front contact layer making electrical contact with the partner layer only through discontinuities in the discontinuous passivation layer, wherein, between the discontinuities in the discontinuous passivation layer, the front contact layer extends, as a continuous layer, over an entirety of the discontinuous passivation layer.
37. The photovoltaic device of claim 36, wherein the front contact layer comprises a transparent conductive oxide.
38. The photovoltaic device of claim 36, further comprising a substrate disposed below the back contact layer.
39. The photovoltaic device of claim 38, wherein (i) the substrate is transparent and/or (ii) the substrate comprises glass.
40. The photovoltaic device of claim 36, further comprising a superstrate disposed over the front contact layer.
41. The photovoltaic device of claim 40, wherein (i) the superstrate is transparent and/or (ii) the superstrate comprises glass.
42. The photovoltaic device of claim 36, wherein the partner layer and the thin-film absorber layer comprise the same material.
43. The photovoltaic device of claim 36, wherein the discontinuous reflector layer comprises at least one of aluminum, silver, titanium dioxide, or zirconium nitride.
44. The photovoltaic device of claim 36, wherein the back contact layer comprises molybdenum.
45. The photovoltaic device of claim 36, wherein the back contact layer comprises a sodium-containing conductive material.
46. The photovoltaic device of claim 45, wherein the sodium-containing conductive material comprises at least one of Mo:NaF or Mo:Na.sub.2MoO.sub.4.
47. The photovoltaic device of claim 36, wherein the discontinuous back reflector is metallic.
48. The photovoltaic device of claim 36, wherein the discontinuous back reflector is non-metallic.
49. The photovoltaic device of claim 36, wherein the discontinuous back reflector is in contact with, but does not form an ohmic contact to, the thin-film absorber layer.
50. A photovoltaic device configured for top illumination by solar energy, the photovoltaic device comprising: a back contact layer comprising a conductive material; a discontinuous back reflector disposed over the back contact layer; a thin-film absorber layer disposed over an in electrical contact with the back contact layer, the thin-film absorber layer (i) having a doping polarity and (ii) comprising CdTe, chalcopyrite, or kesterite, wherein (a) the thin-film absorber layer makes direct electrical contact to the back contact layer through discontinuities in the discontinuous back reflector, and (b) the discontinuous back reflector is positioned to reflect solar energy passing through the thin-film absorber layer back through the thin-film absorber layer in a direction away from the back contact layer; a partner layer disposed over and in electrical contact with the thin-film absorber layer, the partner layer having a doping polarity opposite that of the thin-film absorber layer; a front contact layer disposed over and in electrical contact with the partner layer, the front contact layer (i) comprising a second conductive material and (ii) being disposed over an entirety of the partner layer; and a discontinuous passivation layer disposed between the back contact layer and the thin-film absorber layer, the thin-film absorber layer making electrical contact with the back contact layer only through discontinuities in the discontinuous passivation layer.
51. The photovoltaic device of claim 50, wherein the front contact layer comprises a transparent conductive oxide.
52. The photovoltaic device of claim 50, further comprising a substrate disposed below the back contact layer.
53. The photovoltaic device of claim 52, wherein (i) the substrate is transparent and/or (ii) the substrate comprises glass.
54. The photovoltaic device of claim 50, further comprising a superstrate disposed over the front contact layer.
55. The photovoltaic device of claim 54, wherein (i) the superstrate is transparent and/or (ii) the superstrate comprises glass.
56. The photovoltaic device of claim 50, wherein the partner layer and the thin-film absorber layer comprise the same material.
57. The photovoltaic device of claim 50, wherein the discontinuous reflector layer comprises at least one of aluminum, silver, titanium dioxide, or zirconium nitride.
58. The photovoltaic device of claim 50, wherein the back contact layer comprises molybdenum.
59. The photovoltaic device of claim 50, wherein the back contact layer comprises a sodium-containing conductive material.
60. The photovoltaic device of claim 59, wherein the sodium-containing conductive material comprises at least one of Mo:NaF or Mo:Na.sub.2MoO.sub.4.
61. The photovoltaic device of claim 50, wherein the discontinuous back reflector is metallic.
62. The photovoltaic device of claim 50, wherein the discontinuous back reflector is non-metallic.
63. The photovoltaic device of claim 50, further comprising a sodium-containing layer disposed between the discontinuous passivation layer and the thin-film absorber layer.
64. The photovoltaic device of claim 63, wherein the sodium-containing layer comprises at least one of NaF or Na.sub.2Se.
65. The photovoltaic device of claim 50, wherein the discontinuous back reflector is in contact with, but does not form an ohmic contact to, the thin-film absorber layer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
[0020] FIG. 1 is a schematic cross-section of a portion of a photovoltaic device incorporating a discontinuous passivation layer in accordance with various embodiments of the invention;
[0021] FIG. 2 is a schematic cross-section of a portion of a photovoltaic device incorporating a discontinuous passivation layer and a sodium-containing layer in accordance with various embodiments of the invention;
[0022] FIG. 3A is a schematic plan view of the discontinuous passivation layer of FIG. 1 in accordance with various embodiments of the invention;
[0023] FIGS. 3B-3D are schematic plan views of the structure of FIG. 3A during fabrication thereof in accordance with various embodiments of the invention;
[0024] FIG. 4 is a schematic plan view of the discontinuous passivation layer of FIG. 1 in accordance with various other embodiments of the invention;
[0025] FIG. 5A is a schematic cross-section of a portion of a photovoltaic device incorporating a discontinuous passivation layer and a discontinuous reflector layer in accordance with various embodiments of the invention;
[0026] FIG. 5B is a schematic cross-section of a portion of a photovoltaic device incorporating a discontinuous passivation layer, a discontinuous reflector layer, and a sodium-containing layer in accordance with various embodiments of the invention;
[0027] FIGS. 6A-6D are schematic plan views of the discontinuous passivation layer and discontinuous reflector layer of FIG. 5A during fabrication thereof in accordance with various embodiments of the invention;
[0028] FIGS. 7A and 7B are schematic cross-sections of photovoltaic devices incorporating discontinuous passivation layers in accordance with various embodiments of the invention;
[0029] FIG. 8A is a schematic plan view of the discontinuous passivation layer of FIG. 7A in accordance with various embodiments of the invention;
[0030] FIGS. 8B-8D are schematic plan views of the structure of FIG. 8A during fabrication thereof in accordance with various embodiments of the invention;
[0031] FIG. 9 is a schematic plan view of the discontinuous passivation layer of FIG. 7A in accordance with various other embodiments of the invention;
[0032] FIG. 10 is a schematic cross-section of a portion of a photovoltaic device incorporating two discontinuous passivation layers in accordance with various embodiments of the invention;
[0033] FIGS. 11A-11G are schematic plan views of the structure of FIG. 10 during fabrication thereof in accordance with various embodiments of the invention;
[0034] FIG. 12A is a schematic cross-section of a portion of a photovoltaic device incorporating a discontinuous passivation layer in accordance with various embodiments of the invention; and
[0035] FIG. 12B is a schematic cross-section of a portion of a photovoltaic device incorporating two discontinuous passivation layers in accordance with various embodiments of the invention.
DETAILED DESCRIPTION
[0036] FIG. 1 depicts an exemplary embodiment of the present invention in which a thin-film PV device 100 incorporates a discontinuous passivation layer 110 disposed between a back contact 120 and a thin-film absorber layer 130. The back contact layer 120 may include or consist of, for example, a highly electrically conductive material such as a metal. In some embodiments the back contact layer 120 includes or consists essentially of a refractory metal such as molybdenum (Mo). In some embodiments of the invention, the thin-film PV device 100 also incorporates a sodium-containing layer (as detailed below); in some embodiments, the back contact layer 120 itself contains sodium. For example, the back contact layer 120 may include or consist essentially of Mo:NaF or Mo:Na.sub.2MoO.sub.4. FIG. 1 depicts an embodiment in which the back contact 120 is disposed on a substrate 140 (e.g., soda lime glass), but superstrate embodiments, in which the substrate is disposed above the absorber layer 130 (and the remaining layers of the device) are included in the scope of the present invention. Although not depicted in its entirety in FIG. 1, the thin-film PV device 100 itself includes one or more p-n and/or p-i-n junctions (i.e., homojunctions and/or heterojunctions), and is fabricated from a-Si, CdTe, or a chalcopyrite (Cu(In.sub.xGa)(S,Se).sub.2) such as copper indium gallium selenide (CIGS) or a kesterite (Cu.sub.2(Zn,Fe)Sn(S,Se).sub.4) such as copper zinc tin sulfide (CZTS). For example, for a PV device 100 in which the absorber layer 130 includes or consists essentially of CIGS, the device 100 may include a junction formed via the incorporation of a CdS layer disposed over the absorber layer 130, as discussed below and as illustrated in subsequent figures. Thus, it is to be understood that the PV devices illustrated herein may only show portions of the device relevant to the particular placement of discontinuous passivation layers in accordance with embodiments of the invention and may therefore incorporate additional layers neither shown nor described.
[0037] FIG. 2 depicts a thin-film PV device 200 similar to that depicted in FIG. 1, except for the presence of a sodium-containing layer 210 between the passivation layer 110 and the absorber layer 130. In some embodiments, the presence of a sodium-containing layer 210 (which may include or consist essentially of, e.g., NaF and/or Na.sub.2Se) improves the efficiency of the thin-film PV device 200. The sodium-containing layer 210 may supply sodium to the absorber layer 130 during formation thereof; additional sodium may be supplied by the substrate 140such sodium may diffuse through the back contact layer 120 to the absorber layer 130. Sodium may also be introduced into the PV device 200 in other ways, including as part of the back contact layer 120, or during or after formation of the thin-film absorber layer 130. The sodium-containing layer 210 (and/or other sodium-containing layers described herein) may be continuous (as shown) or discontinuous. Discontinuities in a discontinuous sodium-containing layer 210 may overlap partially or substantially entirely (i.e., be substantially aligned) with discontinuities in a discontinuous passivation layer and/or a discontinuous reflector layer. Alternatively, the discrete regions of a discontinuous sodium-containing layer 210 may partially or substantially entirely overlap the discontinuities in a discontinuous passivation layer and/or a discontinuous reflector layer.
[0038] FIG. 3A depicts a plan view of the discontinuous passivation layer 110 of FIG. 1 after its formation, and FIGS. 3B-3D depict an exemplary process for fabricating the discontinuous passivation layer 110. FIG. 3B depicts the back contact layer 120 (which may itself be formed by, e.g., sputtering upon the substrate 140) prior to the formation of the passivation layer 110. As shown in FIGS. 3C and 3D, the passivation layer 110 may be deposited over the back contact layer 120 as a continuous film (FIG. 3C) and subsequently patterned to form openings that expose portions of the back contact layer 120 (FIG. 3D). The thin-film absorber layer 130 may then be formed over the discontinuous passivation layer 110 and make contact with the exposed portions of the back contact layer 120. In other embodiments, a mask is disposed over the back contact layer 120 such that only portions of the back contact layer 120 are revealed through openings in the mask. The passivation layer 110 may then be deposited over the mask to form discrete portions thereof through the openings in the mask, the regions between the discrete portions being the discontinuities in the passivation layer 110. FIG. 4 is a plan view of another exemplary embodiment of the invention that incorporates a discontinuous passivation layer 110. As shown, the passivation layer 110 has been patterned to form multiple elongated stripes over the back contact layer 120, which is exposed between the passivating stripes. As described above, the absorber layer 130 may be formed over the illustrated structure and make electrical contact with the exposed portions of the back contact layer 120.
[0039] FIGS. 5A and 5B depict exemplary thin-film PV devices 500, 510 in accordance with embodiments of the present invention that incorporate a back optical reflector layer 520 between the discontinuous passivation layer 110 and the back contact 120. The back reflector layer 520 may include or consist essentially of a metal (e.g., aluminum) or another material (e.g., TiO.sub.2) reflective to solar energy. The back reflector 520 reflects solar energy passing through the absorber layer 130 back to the absorber layer 130, thereby increasing the probability of absorption and the efficiency of the PV device. Materials such as aluminum may not form ohmic contacts with absorber layers including or consisting essentially of CIGS, and thus PV devices 500, 510 each incorporate a discontinuous back reflector layer 520 (e.g., patterned like the passivation layer 110) so that the absorber layer 130 may make electrical contact directly with the back contact layer 120. As shown in FIG. 5B, PV device 510 includes the sodium-containing layer 210 described above while PV device 500 omits this layer.
[0040] FIGS. 6A-6D depict portions of an exemplary process, in plan view, for fabricating part of the PV device 500 depicted in FIG. 5A. FIG. 6A depicts the back contact layer 120 (which may itself be formed by, e.g., sputtering upon the substrate 140) prior to the formation of the back reflector layer 520. As shown in FIG. 6B, the back reflector layer 520 may be deposited over the back contact layer 120 either in patterned form (e.g., as a collection of particles or segments) or as a continuous layer that is subsequently patterned to expose portions of the underlying back contact layer 120. The back reflector layer 520 may even be deposited over a mask having openings where the portions of the back reflector layer 520 are desired. The passivation layer 110 may be deposited over the discontinuous back reflector layer 520 (FIG. 6C) and also patterned to reveal the underlying back contact layer 120 (FIG. 6D). (In other embodiments, a mask is disposed over the discontinuous back reflector layer 520 such that all or portions of the discontinuous back reflector layer 520 are revealed through openings in the mask. The passivation layer 110 may then be deposited over the mask to form discrete portions thereof through the openings in the mask, the regions between the discrete portions being the discontinuities in the passivation layer 110.) As shown, at least some of the discontinuities (e.g., holes) in the passivation layer 110 and the back reflector layer 520 overlap, thereby revealing portions of the back reflector layer 120 through both the discontinuous back reflector layer 520 and the discontinuous passivation layer 110. The thin-film absorber layer 130 may then be formed over the discontinuous passivation layer 110 and make electrical contact with the back contact layer 120 through the discontinuities, as shown in FIG. 5A.
[0041] FIG. 7A depicts an exemplary PV device 700 in accordance with various embodiments of the present invention, in which the discontinuous passivation layer 110 is formed between the thin-film absorber layer 130 and a partner layer 710 forming the electrical p-n junction with the absorber layer. For example, if the absorber layer 130 exhibits p-type doping, then the partner layer 710 exhibits n-type doping to form the requisite p-n junction. The partner layer 710 may include or consist essentially of the same material as the absorber layer 130 (thereby forming a homojunction) or a different material (thereby forming a heterojunction). FIG. 7A also depicts a front contact layer 720 utilized to contact the top of the thin-film PV device 700. In embodiments in which solar energy illuminates the absorber layer 130 through the front contact layer 720, the front contact layer is preferably at least substantially transparent to solar energy (or one or more portions of the solar spectrum). Thus, the front contact layer 720 may include or consist essentially of, e.g., a transparent conductive oxide such as indium tin oxide or (B,Al,Ga,In).sub.2O.sub.3:ZnO. In some embodiments of the invention, as shown for PV device 730 of FIG. 7B, in order to reduce carrier recombination at the interface between the partner layer 710 and the front contact layer 720, the discontinuous passivation layer 110 is formed between the partner layer 710 and the front contact layer 720.
[0042] FIG. 8A depicts a plan view of the discontinuous passivation layer 110 of FIG. 7A after its formation, and FIGS. 8B-8D depict an exemplary process for fabricating the discontinuous passivation layer 110. FIG. 8B depicts the absorber layer 130 prior to the formation of the passivation layer 110. As shown in FIGS. 8C and 8D, the passivation layer 110 may be deposited over the absorber layer 130 as a continuous film (FIG. 8C) and subsequently patterned to form openings that expose portions of the absorber layer 130 (FIG. 8D). The partner layer 710 may then be formed over the discontinuous passivation layer 110 and make contact with the exposed portions of the absorber layer 130, as shown in FIG. 7A. FIG. 9 is a plan view of another exemplary embodiment of the invention that incorporates a discontinuous passivation layer 110. As shown, the passivation layer 110 has been patterned to form multiple elongated stripes over the absorber layer 130, which is exposed between the passivating stripes. As described above, the partner layer 710 may be formed over the illustrated structure and make electrical contact with the exposed portions of the absorber layer 130.
[0043] Embodiments of the invention incorporate multiple different discontinuous passivation layers 110 disposed at different locations within the PV device structure. FIG. 10 depicts the cross-section of an exemplary PV device 1000 that incorporates a first discontinuous passivation layer 110-1 between the thin-film absorber layer 130 and the partner layer 710, as well as a second discontinuous passivation layer 110-2 between the partner layer 710 and the front contact layer 720. Although not depicted in FIG. 10, such structures may even include a discontinuous passivation layer (and/or back reflector layer) disposed between the thin-film absorber layer 130 and the back contact layer 120 (as shown in FIGS. 1, 5A, and/or 5B) in addition to the two passivation layers 110-1, 110-2 (or instead of one or the other of them). The patterns of the individual passivation layers 110 need not have the same geometry, feature size, or pitch.
[0044] FIGS. 11A-11G depict an exemplary process for fabricating the discontinuous passivation layers 110-1, 110-2 depicted in FIG. 10. FIG. 11A depicts the absorber layer 130 prior to the formation of the first passivation layer 110-1. As shown in FIGS. 11B and 11C, the first passivation layer 110-1 may be deposited over the absorber layer 130 as a continuous film (FIG. 11B) and subsequently patterned to form openings that expose portions of the absorber layer 130 (FIG. 11C). (In other embodiments, a mask is disposed over the absorber layer 130 such that portions of the absorber layer 130 are revealed through openings in the mask. The first passivation layer 110-1 may then be deposited over the mask to form discrete portions thereof through the openings in the mask, the regions between the discrete portions being the discontinuities in the first passivation layer 110-1.) The partner layer 710 may then be formed over the first discontinuous passivation layer 110-1 and make contact with the exposed portions of the absorber layer 130, as shown in FIG. 11D (and FIG. 10). As shown in FIGS. 11E and 11F, the second passivation layer 110-2 may be deposited over the partner layer 710 as a continuous film (FIG. 11E) and subsequently patterned to form openings that expose portions of the partner layer 710 (FIG. 11F). (In other embodiments, a mask is disposed over the partner layer 710 such that all or portions of the partner layer 710 are revealed through openings in the mask. The second passivation layer 110-2 may then be deposited over the mask to form discrete portions thereof through the openings in the mask, the regions between the discrete portions being the discontinuities in the second passivation layer 110-2.) The front contact layer 720 may then be formed over the second discontinuous passivation layer 110-2 and make contact with the exposed portions of the partner layer 710, as shown in FIG. 11G (and FIG. 10). The patterns of the individual passivation layers 110-1, 110-2 need not have the same geometry, feature size, or pitch.
[0045] FIGS. 12A and 12B depict exemplary PV devices 1200, 1210 in accordance with embodiments of the present invention in which the discontinuous passivation layer 110 is formed (e.g., deposited) as a collection of particles or other discrete portions, rather than deposited as a uniform layer and subsequently patterned. As shown, in PV device 1200 the passivation layer 110 is deposited as a collection of particles on the thin-film absorber layer 130 and subsequently covered with the partner layer 710, which makes electrical contact with the absorber layer 130 in the regions between the particles (i.e., the discontinuities in the discontinuous passivation layer 110). As shown in FIG. 12B, PV device 1210 incorporates a first passivation layer 110-1 similar or identical to the passivation layer 110 in PV device 1200, as well as a second passivation layer 110-2 formed over the partner layer 710 and subsequently patterned prior to formation of the front contact layer 720. In order to form the discontinuous passivation layers 110 in PV devices 1200, 1210 as a collection of discrete portions, the passivation layer material may be deposited over the device structure through a mask having openings where the passivation layer 110 is desired; after formation of the resulting discrete portions, the mask is removed and the additional layers of the PV device structure are formed.
[0046] The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.
