UTILIZING SUCH STRUCTURE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application No.

62/677,834, filed May 30, 2018, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] Presently there are three different types of thin-film photovoltaic (PV) modules with monolithically series interconnected solar cells that are being

commercially produced at various volumes. They all have a similar generic structure. Figure 1 shows, schematically, the cross section of an exemplary embodiment of such prior art modules through the interconnect section. The serial interconnect is achieved by three scribes pi (5), p2 (6), p3 (7) performed after the deposition of the bottom ohmic conductor (2) (also sometimes referred to as the "bottom ohmic contact"), the photovoltaic (PV) structure (3) and the top ohmic conductor (4) (also sometimes referred to as the "top ohmic contact") respectively.

[0003] The scribes pi (5) and p3 (7) separate the bottom (2) and the top (4) conductors of adjacent cells, while p2 (6), when filled, allows series connection of the two adjacent cells. Here the PV structure (3) refers to a stack of two thin-film semiconductor layers, an absorber and an emitter, forming a p-n junction. Light is absorbed by the absorber, generating electron-hole pairs that are swept to the contacts 4 and 5 by the electric field in the junction region (i.e. junction field) resulting in a DC current flowing in the external circuit connected to contacts 4 and 5.

[0004] These products are generally referred to by the name of their absorbers.

Oldest is the a-Si (amorphous silicon) module, where the substrate (1) is glass such as, a soda-lime glass, and the bottom contact (2) is, most commonly, a Sn02: F (fluorine doped tin oxide) film which is transparent. The PV structure (3) is an a-Si p-i-n junction, and the top contact (4) may be Al, ZnO/AI, or Ag. Because of the transparent nature of the substrate (1) and the bottom ohmic conductor (2) and the non- transparent nature of the top ohmic contact (4), the module operates in "superstate mode," meaning that light enters the device from the substrate side. This allows successful development of scribing technologies utilizing lasers incident on the glass substrate having the proper wavelength and operational parameters such that the absorption of the beam energy is localized at the interface between the film to be removed and the underlying transparent (to the laser wavelength) structure. That way, the film is removed through a micro-explosion effect without excessive heating of, and the thermal damage to, the region surrounding the scribe, thereby avoiding module performance loss associated with such thermal damage.

[0005] As early as 1991, a-Si PV modules of 5ft X 2.5ft in size have been manufactured in a prototype facility utilizing this type of all-laser scribing technology.

In this case, a Q-switched Nd :YAG laser at 1064 nm was used to pattern/form the pi scribe, and a frequency doubled Q-switched Nd :YAG laser at 532 nm was used to pattern/form the p2 and p3 scribes. Scribe widths and the separation between them were in the order of 100 pm.

[0006] CdTe based modules also produced commercially, have for the purposes of monolithic interconnection the same structure as that of a-Si modules. The substrate is glass, the bottom contact is SnC>2: F (sometimes bi-layer of SnC>2 of different conductivity), the PV structure is a CdS-CdTe junction, and the top contact is a Ni/AI layer. An IR laser is used to form all three scribes (approx. 100 pm width), though the interconnect process details may be somewhat more elaborate due to the differences in materials and film deposition processes.

[0007] A third type of module is based on the family of CuInSe2 (CIS) absorbers having a general chemical formula of (Cu,Ag)(In,Ga)(S,Se)2. Such modules, having glass substrates, with Cu(In,Ga)Se2 (CIGS) absorbers are commercially available, albeit in limited volume. The PV structure is commonly a CIGS-CdS junction, although there are some photovoltaically-active structures in which the emitter is different than CdS. However, modules of these types have major differences from those discussed above in that the bottom ohmic contact is a Mo thin-film and the top ohmic contact is a transparent conductor bi-layer of very thin, such as having a thickness in the range of 20 nm to 200 nm or approximately 50 nm, intrinsic zinc oxide (i-ZnO) coupled with aluminum or boron doped zinc oxide (i-ZnO/ZnO(AI or B)) or coupled with indium tin oxide (i-ZnO/In2C>3:SnC>2). They operate in "substrate mode," meaning that light enters the device from the film side. Serial interconnect is still the same as shown in Figure 1. However, in the fabrication of the interconnect scribes, only the pi can be made using lasers incident on the glass substrate. Again, Nd :YAG is quite adequate for this purpose. The other scribes, p2 and p3 require film side scribing. These two scribes have historically been obtained by mechanical means by scratching the films using a stylus, resulting in loss of module performance and reproducibility/yield and increasing manufacturing cost. Research on robust and low cost film side scribing processes compatible with high volume manufacturing by mechanical means, or lasers continues to this date.

[0008] A new type of solar cell based on absorbers having a general chemical formula of Cu2ZnSn(S,Se) ₄ (CZTS) is presently being researched in various

laboratories. Solar cell configuration based on these absorbers is the same as that of CIS type solar cell and, as such, the module interconnect for CIGS is directly applicable to this technology when it moves to the module manufacturing stage.

[0009] Hence, there is a continued need for new and improved thin-film photovoltaic device structures and processes for the manufacture of modules comprising thin-film photovoltaic devices having such structures, including processes for scribing monolithically interconnected devices during manufacture of CIS and CZTS type solar cells module.

SUMMARY OF THE INVENTION

[0010] One aspect of the invention provides a thin-film photovoltaic device structure comprising a substrate having a first surface and a second surface, with a bi- layer bottom contact disposed over the substrate. The bi-layer bottom contact comprises a first transparent conductor layer disposed over and in contact with at least a portion of the first surface of the substrate and an opaque conductor layer, which may comprise two or more sub-layers, disposed over and in contact with at least a portion of the first transparent conductor layer. A multi-layer, photovoltaically-active, thin-film structure is disposed over and in ohmic contact with at least a portion of the opaque conductor layer. A second transparent conductor layer is disposed over and in ohmic contact with at least a portion of the multi-layer, photovoltaically-active, thin- film structure. The substrate and the first transparent conductor layer are substantially transparent to one or more predetermined wavelengths of light corresponding to one or more scribing laser wavelengths. The second transparent conductor layer is

substantially transparent to at least a portion of the solar spectrum.

[0011] The bi-layer bottom contact may comprise two or more opaque conductor sub-layers such that the contact between the photovoltaically-active, thin- film structure and the adjacent sub-layer is ohmic.

[0012] Another aspect of the invention provides a thin-film photovoltaic module comprising the thin-film photovoltaic device structure having a substrate configuration, as described hereinabove. A number of thin-film photovoltaic devices, having the device structure, as described above, may be monolithically series connected by incorporating a number of grooves or scribes into the structure to form a thin-film photovoltaic module. The terms "groove" or "scribe" may be used interchangeably herein, with neither term implying any limitation with respect to geometry or method of formation, except as expressly stated herein. For example, two series connected device can be obtained by incorporating three scribes, three series connected device require six scribes, etc. A first scribe (pi) may be disposed through the bi-layer bottom contact, such that at least a portion of the multi-layer, photovoltaically-active, thin-film structure is disposed over and in contact with at least a portion of the substrate in the first scribe. A second scribe (p2) may be disposed through the opaque conductor layer and the overlaying multi-layer photovoltaically-active thin-film structure, such that at least a portion of the second conductor layer is disposed over and in contact with at least a portion of the first transparent conductor layer in the second scribe. A third scribe (p3) may be disposed through the opaque conductor, the overlaying multi-layer, photovoltaically-active, thin-film structure and the second transparent conductor layer. The first, the second and the third scribes are preferably parallel to each other. The first scribe (pi) separates the layer of bi-layer bottom contact into a plurality of bi-layer bottom contacts of a plurality of individual series- connected photovoltaic cells. The second scribe (p2), when filled, forms an

interconnect between the second transparent conductor layer of a first photovoltaic cell of the plurality of series-connected photovoltaic cells and the first transparent conductor layer of a second photovoltaic cell adjacent to the first cell. The third scribe (p3) separates the first photovoltaic cell from the second photovoltaic cell.

[0013] In various embodiments, each of the scribes (pi, p2, and p3) is laser- scribed. The first, the second and the third scribes may each be spatially separated from one another by a non-scribed area, or at least one pair of the second and the third scribes may be spatially adjacent to one another without a non-scribed area between them. The multi-layer, photovoltaically-active, thin-film structure may comprise a first layer disposed over and in contact with at least a portion of the opaque conductor layer; and a last layer disposed over the first layer and in contact with at least a portion of the second transparent conductor layer. In specific embodiments, the substrate may comprise a glass or a polyimide film, the first transparent conductor layer may comprise at least one of fluorine doped tin oxide (SnC>2: F), indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:AI), and boron doped zinc oxide (ZnO: B), and the opaque conductor layer may comprise one of molybdenum (Mo), tungsten (W), or tantalum (Ta). In some embodiments, the opaque conductor layer may comprise one of molybdenum (Mo), tungsten (W), or tantalum (Ta) containing up to 20 atomic percent oxygen. The second transparent conductor layer may comprise fluorine-doped tin oxide (SnC>2: F), indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:AI), boron doped zinc oxide (ZnO: B), or a combination of one or more thereof.

[0014] The second transparent conductor layer may comprise a layer of intrinsic zinc oxide (i-ZnO) having a thickness between 20 nm to 200 nm, disposed over and in contact with at least a portion of the multi-layer, photovoltaically-active, thin-film structure and a layer of at least one of fluorine doped tin oxide (SnC>2:F), indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:AI), and boron doped zinc oxide (ZnO: B) disposed over the layer of intrinsic zinc oxide. In an embodiment, the second transparent conductor is a bi-layer of very thin, approximately 50 nm, intrinsic zinc oxide (i-ZnO) coupled with either aluminum or boron doped zinc oxide (i-ZnO/ZnO(AI or B)) or coupled with indium tin oxide (i-ZnO/In2C>3:SnC>2). The multi-layer, photovoltaically-active, thin-film structure may comprise an absorber having a general chemical formula of (Cu,Ag)(In,Ga)(S,Se)2 or Cu2ZnSn(S,Se) ₄ .

[0015] Another aspect of the invention comprises a method for creating a photovoltaic module as described herein. The method comprises the steps of (a) providing a substrate, (b) forming the bi-layer bottom contact over the substrate by forming a first transparent conductor layer over and in contact with at least a portion of the first side of the substrate, and forming an opaque conductor layer over and in contact with at least a portion of the first transparent conductor layer; then (c) forming a multi-layer, photovoltaically-active, thin-film structure over and in ohmic contact with at least a portion of the opaque conductor layer; and (d) forming a second transparent conductor layer over and in ohmic contact with at least a portion of the multi-layer, photovoltaically-active, thin-film structure. The substrate and the first transparent conductor layer are substantially transparent to one or more predetermined

wavelengths of light corresponding to one or more scribing laser wavelengths, the second transparent conductor layer is substantially transparent to at least a portion of the solar spectrum, and the thin-film photovoltaic module is in a substrate

configuration.

[0016] The method may further comprise performing a first laser-scribing step from the second side of the substrate before step (c), to form a first laser-scribed scribe through the bi-layer of the first transparent conductor layer and the opaque conductor layer; performing a second laser-scribing step from the second side of the substrate before step (d), to form a second laser-scribed scribe through the opaque conductor layer and the multi-layer, photovoltaically-active, thin-film structure; and performing a third laser-scribing step from the second side of the substrate after step (d), to form a third laser-scribed scribe through the opaque conductor layer, the multi- layer, photovoltaically-active, thin-film structure and the second transparent conductor layer, to form a plurality of photovoltaic cells connected in series. The first, the second and the third laser-scribed scribes are preferably parallel to each other. The first laser- scribed scribe (pi) separates bi-layer bottom contact into a plurality of bi-layer bottom contacts of a plurality of individual series-connected photovoltaic cells. The second laser-scribed scribe (p2), when filled, forms an interconnect between the second transparent conductor layer of a first photovoltaic cell of the plurality of individual series-connected photovoltaic cells and the first transparent conductor layer of a second photovoltaic cell adjacent to the first cell. The third laser-scribed scribe (p3) separates the first photovoltaic cell from the second photovoltaic cell.

[0017] At least one of the first, second or third laser-scribing step may be performed using a scribing system having one or more operational parameters different from that of the other laser-scribing steps. For a glass substrate, at least one of the first, the second and the third laser-scribing steps may be performed using a Nd :YAG or Nd :Vanadate laser with a laser scribing wavelength of 532 nm or 1064 nm or 1319 nm. For a polyimide substrate, at least one of the first, the second and the third laser- scribing steps are performed using a Nd :YAG or Nd : Vanadate laser with the laser scribing wavelength of 1064 nm or 1319 nm. Each of the first, the second and the third laser-scribed scribes may be spatially separated from one another by a non- scribed area, or pairs of the second and the third laser-scribed scribes may be formed spatially adjacent to one another without a non-scribed area between them.

[0018] The step of forming the first transparent conductor layer may comprise forming at least one of fluorine doped tin oxide (SnC>2:F), indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:AI), boron doped zinc oxide (ZnO: B), and the step of forming the opaque conductor layer may comprise forming at least one of molybdenum (Mo), tungsten (W), or tantalum (Ta) layer. In some embodiments, the step of forming the opaque conductor layer may also comprise forming at least one of molybdenum (Mo), tungsten (W), or tantalum (Ta) layer containing up to 20 atomic percent oxygen. The step of forming the multi-layer, photovoltaically-active, thin-film structure may comprise forming an absorber layer having a general chemical formula of

(Cu,Ag)(In,Ga)(S,Se)2 or Cu2ZnSn(S,Se) ₄ and forming an emitter layer of materials such as CdS or emitter layers of other formulations, over the absorber layer. The step of forming the second transparent conductor layer may comprise forming a layer of at least one of fluorine doped tin oxide (SnC>2:F), indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:AI), and boron doped zinc oxide (ZnO: B) over and in contact with at least a portion of the multi-layer, photovoltaically-active, thin-film structure, and may further comprise forming a layer of intrinsic zinc oxide (i-ZnO) having a thickness between 20 nm to 200 nm, disposed over and in contact with at least a portion of the multi-layer, photovoltaically-active, thin-film structure and forming a layer of at least one of fluorine doped tin oxide (SnC>2:F), indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:AI), and boron doped zinc oxide (ZnO: B) over the layer of intrinsic zinc oxide. In an embodiment, the second transparent conductor is a bi-layer of very thin, approximately 50 nm, intrinsic zinc oxide (i-ZnO) coupled with either aluminum or boron doped zinc oxide (i-ZnO/ZnO(AI or B)) or coupled with indium tin oxide (i- ZnO/In2C>3:SnC>2).

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrates one (several) embodiments(s) of the invention, and together with the written description, serve to explain certain principles of the invention.

[0020] Fig. 1 is a schematic illustration of a cross sectional view of the interconnect region of an exemplary prior art generic PV module with monolithically interconnected photovoltaic cells.

[0021] Fig. 2A is a schematic illustration of a cross-sectional view of a portion of an exemplary thin-film photovoltaic device, specifically an exemplary CIS solar cell with a bi-layer bottom contact.

[0022] Fig. 2B is a schematic illustration of a cross-sectional view of a portion of another exemplary thin-film photovoltaic device, specifically an exemplary CIS solar cell with a bi-layer bottom contact, wherein the bi-layer bottom contact comprises at least one transparent conductor layer and two or more opaque conductor sub-layers.

[0023] Fig. 3A is a schematic illustration of a cross-sectional view of the interconnect region of an exemplary thin-film photovoltaic module based on a CIS solar cell structure having spatially separate pi, p2, and p3 scribes.

[0024] Fig. 3B is a schematic illustration of a cross-sectional view of the interconnect region of an exemplary thin-film photovoltaic module based on a CIS solar cell structure having spatially overlapped p2 and p3 scribes.

[0025] Figs. 4A-4F show a method for creating the series interconnect of two devices in a thin-film photovoltaic module using laser scribing from the substrate side for making all scribes, in accordance with various embodiments of the present invention. LI, L2, and L3 represent scribing laser beams incident on the specific interfaces to form the pi, p2, and p3 scribes respectively. DETAILED DESCRIPTION OF THE INVENTION

[0026] Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

[0027] As used herein, the term "photovoltaically-active structure" or "PV structure" used interchangeably with "multi-layer, photovoltaically-active, thin-film structure" refers to a stack of at least two thin-film semiconductor layers, an absorber and an emitter, forming a p-n junction. As used herein, the term "thin film photovoltaic device structure" refers to a stack of layers including "PV structure," used to form a "photovoltaic device," also referred to herein as a "device," a "photovoltaic cell," or a "solar cell"; and the term "thin-film photovoltaic module refers to two or more interconnected "photovoltaic cells (solar cells)" or two or more interconnected thin-film photovoltaic devices.

[0028] As used herein, the term "ohmic contact" refers to a contact or a layer forming an electrical junction with another conductor or semiconductor, such that charge can flow easily, with substantially no resistance or low resistance, through the electrical junction with an identical linear current-voltage relationship in both directions, without blockage due to rectification or excess power dissipation due to voltage thresholds. Furthermore, as used herein, the phrase "in ohmic contact with" is intended to mean that a layer makes a contact with another layer in a photovoltaically- active, thin-film structure, where the contact can form an electrical junction such that charge can flow easily, with substantially no resistance or low resistance and with an identical linear current-voltage relationship through the electrical junction in both directions, without blockage due to rectification or excess power dissipation due to voltage thresholds.

[0029] As used herein, the terms "groove" or "scribe," used interchangeably, refer to a discontinuity between adjacent areas of material, such as may be formed by laser scribing. Certain grooves or scribes exist as an absence of material separating adjacent areas at some point in the manufacturing processes described herein, but may be filled at a later time in the process (such as with a different material than that which was originally removed during a scribing step). The discontinuity may still be referred to herein as a "groove" or "scribe," even after it has been completely or partially filled, and thus use of the terms "groove" or "scribe" herein does not specifically denote a filled or unfilled state, unless expressly indicated. Additionally, the first scribe (pi) separates the layer of bi-layer bottom contact into a plurality of bi-layer bottom contacts of a plurality of individual series-connected photovoltaic cells. The second scribe p2, when filled, forms an interconnect between the second transparent conductor layer of a first photovoltaic cell of the plurality of individual series-connected photovoltaic cells and the first transparent conductor layer of a second photovoltaic cell adjacent to the first photovoltaic cell. The third scribe (p3) separates the first photovoltaic cell from the second photovoltaic cell.

[0030] One aspect of the invention is a new thin-film device structure for photovoltaic (PV) application that has a substrate configuration i.e. light incoming from the film side, on a substrate that is optically transparent. The top ohmic contact of the device is a transparent conducting film in contact with a multilayer, photovoltaically- active, thin-film structure. In some embodiments, the top ohmic contact is a bi-layer of very thin, such as having a thickness in the range of 20 nm to 200 nm (such as approximately 50 nm), intrinsic zinc oxide (i-ZnO) coupled with either aluminum or boron doped zinc oxide (i-ZnO/ZnO(AI or B)) or coupled with indium tin oxide (i- ZnO/In2C>3:SnC>2). The bottom contact, on the substrate, is a bi-layer bottom contact comprising a first transparent conductor layer and an opaque (non-transparent) conductor layer (such as metal/metal-alloy) making an ohmic contact to the multilayer, photovoltaically-active, thin-film structure.

[0031] As used herein, the term "bi-layer bottom contact" refers to a bottom contact comprising at least two conductor layers having two different optical transparencies. In an embodiment, the "bi-layer bottom contact" comprises two layers, a single transparent conductor layer formed on the substrate and a single opaque conductor layer formed on the single transparent conductor and in an ohmic contact with the multilayer, photovoltaically-active, thin-film structure. In another embodiment, the "bi-layer bottom contact" structure comprises a single transparent conductor layer and an opaque conductor layer comprising two or more sub-layers such that:

a. a first sub-layer is an opaque conductor, disposed over and in contact with the first transparent conductor,

b. a last sub-layer is also an opaque conductor, and is in ohmic contact with at least a portion of the multi-layer, the photovoltaically-active thin-film structure, which is disposed over the last sub-layer, and

c. one or more other sub-layers, in between the first and the last sub-layers, the one or more other sub-layers having electrical properties such that they do not impede the flow of the current generated by the photovoltaic device. [0032] Such sub-layers may be provided for any reason, and in some

embodiments may provide some benefit in perfecting the structure in terms of performance or manufacturing. In one embodiment, the sub-layers may reduce detrimental interfacial reactions during the formation of the absorber layer, as the absorber layer is typically formed at a high temperature. For example, providing a molybdenum (Mo) layer containing oxygen may minimize or prevent chemical reaction of Mo at the interface during the formation of the absorber layer. In another embodiment, Mo with additional sodium may optimize operation of the absorber layer.

[0033] By way of example, a suitable three-sublayer opaque conductor would consist of a first sub-layer of Mo containing oxygen, a second sub-layer of Mo containing sodium, and a last sub-layer of Mo containing oxygen. Hence, in an embodiment of the present invention, the "bi-layer bottom contact" structure may comprise a single transparent conductor layer and an opaque conductor layer comprising three sublayers - a first sub-layer of Mo containing oxygen, a second sub- layer of Mo containing sodium, and a last sub-layer of Mo containing oxygen.

[0034] Figures 2A and 2B, show, schematically, the cross-sections of such devices, in accordance with various embodiments of the present invention. By way of example, Figure 2A is the cross-section of an exemplary thin-film photovoltaic device, namely a CIS solar cell with the addition of a transparent conductor layer (9) (e.g. a transparent conductive oxide such as SnC>2: F) between the substrate (8) and an opaque conductor layer (10) (e.g. Mo), with the transparent conductor layer (9) and the opaque conductor layer (10) in combination forming a bi-layer bottom contact. Figure 2B is the cross-section of an exemplary thin-film photovoltaic device where the opaque conductor layer (10) is made up of a number of sub-layers (10a to lOz).

[0035] The first transparent conductor layer (9) doesn't change the operating principle of the photovoltaic cells of the type illustrated in Figure 1, but plays an important role in the manufacture of the PV modules. More specifically, it allows the use of lasers incident on the transparent (e.g. glass) substrate (8) to perform all three scribes (pi (13), p2 (14), p3 (15)) without the need of film side differential removal of the films.

[0036] In general, although other components of the thin-film photovoltaic device such as the substrate, the first transparent conductor layer, the second transparent conductor layer may referred to herein as a "layer," of the term layer is not limited to only a single physical layers of a single material, but may comprise a plurality of sub-layers that together perform the functional operations required of the layer as described herein. Additional layers or sub-layers may be present in the thin-film photovoltaic device that either do not negatively interfere with the functional operations of the layers or the overall operation of the thin-film photovoltaic device or that further enhance functional operations of the layers or the overall operation of the thin-film photovoltaic device, as described herein.

[0037] Figures 3A and 3B schematically illustrates, again by way of example, the cross-sectional view of the interconnect region of an exemplary thin-film

photovoltaic module having a transparent conductive oxide layer between the substrate (1) and an opaque conductor layer (10), with three scribes (pi (13), p2 (14), p3 (15)) in two different configurations. In particular, Fig. 3A illustrates spatially separated pi (13), p2 (14), and p3 (15) scribes and Fig. 3B illustrates spatially overlapped p2 (14) and p3 (15) scribes.

[0038] In the interconnect region of the PV module based on the thin-film photovoltaic device, a CIS solar cell of Figures 2A and 2B, laser beams (LI, L2, and L3) from a Nd :YAG laser operating in the IR can be used for all three scribes (13, 14, and 15) as depicted in Figures 4A-4F. As shown in Figures 4A-4F, the arrows on the laser beams (LI, L2, and L3) point to the interfaces, where the laser beams are incident to form pi, p2, and p3 scribes. More specifically, Figure 4A shows formation of a "bi-layer bottom contact" structure over the substrate (8) comprising a single transparent conductor layer (9) and an opaque conductor layer (10). As shown in Figure 4B, the scribe pi (13') is produced after the deposition of the opaque conductor layer (10)

(e.g., Mo film) with a laser beam (LI) assisted micro-explosion at the interface between the substrate (8) and the first transparent conductor layer (9), e.g. SnC>2: F layer, thereby dividing the layer of bi-layer bottom contact into two bi-layer bottom contacts. Figure 4C shows that deposition of the multilayer photovoltaically-active, thin-film structure (11) (e.g. CIGS/CdS film) fills the scribe pi (13'), thereby

separating the bi-layer bottom contacts into two regions, for the formation of adjacent photovoltaic cells (21 and 22), as shown in Figure 4F.

[0039] Figure 4D shows that the scribe p2 (14') is produced next after the deposition of the multilayer, photovoltaically-active, thin-film structure (11) (e.g.

CIGS/CdS films) using laser beam (L2) assisted micro-explosion at the interface between the first transparent conductor layer (9) and the opaque conductor layer (10). Formation of scribe p2 (14') is followed by deposition of the second transparent conductor layer (12) (e.g. i-ZnO/ZnO:AI films), which in turn fills the scribe p2 (14') to form an interconnect (14), as shown in Figure 4E, between the second transparent conductor layer (12) of a first cell of the plurality of individual series-connected photovoltaic cells and the first transparent conductor layer (9) of a second cell adjacent to the first photovoltaic cell, such as adjacent photovoltaic cells (21 and 22) shown in Figure 4F.

[0040] Figure 4F shows that the scribe p3 (15') is formed after the deposition of the second transparent conductor layer (12) by the laser beam (L3) assisted micro- explosion at the interface between the opaque conductor layer (10) and the first transparent conductor layer (9), i.e. Mo-SnC>2: F interface, which is left unfilled or filled with an insulator to electrically isolate the second transparent conductor layer (12) of the first photovoltaic cell (21) from the second transparent conductor layer (12) of the second photovoltaic cell (22).

[0041] In an embodiment, a procedure similar to that shown in Figures 4A-4F can be used to make the overlapping scribes, as shown in Figure 3B. The latter gives another degree of freedom in optimizing performance/manufacturability. The operational parameters of the laser scribing system are optimized for each scribe such that the absorption of the beam energy is localized at the interface between the film to be removed and the underlying transparent (to the laser wavelength) structure. The operational parameters of the laser scribing system may be optimized such that at least one of the first, the second and the third laser-scribing step is performed using one or more operational parameters different from that of the other laser-scribing steps. The use of different operational parameters of a laser scribing system for different scribes to localize the absorption of the beam energy at the desired interface for each scribe is well known to those of skill in the art, including but not limited to modifying one or more operational parameters such as filters, laser pulse beam intensity, repetition rate of laser pulses (in the case of Q-switched lasers), and speed of the scanning table / sample stage to achieve the desired results.

[0042] Referring back to Figures 3A and 3B, the transparency of the first transparent conductor layer (9), such as SnC>2: F layer permits laser beams incident on the substrate (8) such as glass to reach and remove the opaque conductor layer (10) (e.g. Mo layer) to produce p2 (14) and p3 (15) scribes. That way serial connection between the adjacent cells is achieved by contacting the second transparent conductor layer (12) (i-ZnO/ZnO:AI layer) and the first transparent conductor layer (9) (e.g. SnC>2: F layer) through the p2 (14) scribe. The p3 (15) scribe provides isolation of the top ohmic contacts (second transparent conductor layer (12)) of the adjacent photovoltaic cells. This avoids the need for film side scribing to obtain p2 (14) and p3 (15) and therefore substantially improves manufacturing of this type of PV modules comprising a plurality of photovoltaic cells. The first transparent conductor layer (9) (e.g. SnC>2: F) can fulfill its function within a quite wide window in its electrical and optical properties. It has to carry the module current only for a maximum distance of three-scribe width between two adjacent cells. Furthermore, it is not necessary for the optical transmission to cover a very wide spectrum, as long as it transmits the laser beams for p2 (14) and p3 (15) scribes.

[0043] In one embodiment, the second transparent conductor is a bi-layer of very thin, approximately 50 nm, intrinsic zinc oxide (i-ZnO) coupled with either aluminum or boron doped zinc oxide (i-ZnO/ZnO(AI or B)) or coupled with indium tin oxide (i-ZnO/In2C>3:SnC>2). The solar cell operating in the substrate configuration also has important implications in the choice of the substrate. Regular glass, such as, soda- lime glass is acceptable. Other insulators having similar low surface roughness and optical transmission in the IR rather than in the full solar spectrum are also acceptable as long as the scribing is performed with laser lines in the IR, such as 1064 nm or 1319 nm lines of the Nd :YAG laser and/or 1064 nm or 1342 nm lines of the Nd : Vanadate laser. In view of this, polyimide films such as Kapton® (DuPont, USA) and Upilex® (Ube, Japan) may be suitable substrate materials. For example, a 2 mil (50 pm) Upilex® film has 68% transmission at 900 nm and approximately 75% to 80% at 1064 nm. Accordingly, CIGS based flexible modules on polyimide substrates can be made in substrate configuration utilizing the new solar cell structure described in the present disclosure. Roll-to-roll production technologies may substantially reduce the

manufacturing cost of PV modules on flexible polyimide substrates. Further, due to their high power-to-weight ratio, such flexible modules may find terrestrial applications as portable and wearable power sources in civilian and military use, and also in space applications. They may also be used in large-scale terrestrial power generation, particularly when incorporated in a rigid encapsulation system such as used for crystalline Si solar modules.