Photovoltaic device

Abstract

A solar photovoltaic module or monolithically interconnected module (MIM) consists of densely packed solar cells interconnected in series configuration by 3 scribing processes (P1, P2, P3) on the same substrate. The interconnection of the cells is achieved by an opening formed between the 1st conductive electrode of the nth cell and the 2nd conductive electrode of the (n+1)th cell of the cell pack. To complete the interconnection, the electrical isolation of each cell's electrodes is scribed. The novel structure of the present invention is accomplished by converting the interconnection zone's electrical behavior from a reverse-connected diode to a resistor under a high enough application of voltage.

Description

[0001] PHOTOVOLTAIC DEVICE

[0002] Technical Field

[0003] This invention is related to the field of thin-film photovoltaic devices that convert sunlight into electricity. More specifically, it involves the development of a series-connected monolithic module structure enabling a fabrication route with no need to scribe a P2 interconnection zone.

[0004] State of the Art

[0005] Lab-scale small-area photovoltaic devices cannot meet the electrical requirements of home appliances. To scale up the energy production capacity, large-area Monolithic Interconnected Modules (MIMs) have emerged. MIMs are densely packed arrays of series of interconnected photovoltaic (PV) cells that share the same substrate. Owing to the series-connected configuration, the output voltage of a MIM is linearly dependent on the number of the series- connected cells. The photogenerated current of MIMs is limited to one cell in the assembly. This structure enables much lower joule energy loss arising from the current flowing through the contacts. These devices have been extensively developed during the past few decades.

[0006] A state-of-the-art MIM comprises 6 layers: substrate, the first conductive layer, the charge transport layer, the photo absorber (known as the absorber) layer, the opposite charge transport layer, and the second conductive layer. At least one of the conductive layers should be transparent to the spectral range that matches the active layer’s bandgap and is absorbed by the photoabsorber layer. The fabrication method of a MIM starts with the deposition of the first conducting layer on a substrate. Then, processing proceeds with the patterning of the first conductive layer, the so-called Pl, utilized to create isolated contacts. Optionally, the next step is the deposition of the charge transport layer. The charge transport layer can consist of multiple layers or none. Next, the absorber layer is deposited. After that, optionally, the opposite charge transport layer is deposited. The opposite charge transport layer can consist of multiple layers or none. In conventional PV module devices, P2 scribing is performed by removing the layers above the first conducting layer. P2 scribing is done either as a parallel line to Pl or as dot openings adjacent to Pl . The second conducting layer is deposited on top of the active layer or on top of the charge transport layer, if used. The last step of the processing is scribing the 2ndconducting layer. After that step, the series interconnection of the adjacent cells is finalized. Figures 1 and 2 demonstrate the steps of fabricating conventional PV module devices. The main problem of having an interconnection processing is the need for excessive time to optimize individual scribing or doping parameters and the need for interrupting the fabrication steps. In addition to time and labor costs, material removal can cause exposure to specks or vapors of toxic materials in many solar cell technologies such as perovskite, CdTe, and CIGS. Lastly, direct contact between the bottom-most conductive material and absorber layer is formed at a conventional P2 interconnection site. Less stable conductive materials such as copper or silver are known to diffuse into the active layer and accelerate cell degradation over time.

[0007] US9452992B2 discloses a process that increases the conductivity of the interconnection path by laser welding, instead of laser scribing. By applying laser irradiation to the aimed interconnection path, the semiconductor thin-film material becomes more metallic.

[0008] US20090145472A1 discloses that the conductivity of the interconnection path is increased by a doping method. Interconnection path conductivity is increased by introducing dopant elements.

[0009] Figures

[0010] FIG. 1 : Flow chart for fabrication of conventional PV (Prior art)

[0011] FIG. 2: Demonstration of steps for fabrication of conventional PV (Prior art) a) Deposition of the first conducting layer on a substrate b) Laser scribing (Pl) to isolate the first conducting layer of adjacent cells c) Deposition of the charge transport layer d) Deposition of the absorber layer on top of the charge transfer layer e) Deposition of the opposite charge transport layer on the absorber layer f) Laser scribing (P2) to create an interconnection path between the adjacent cells. g) Deposition of the second conducting layer on top of the opposite charge transport layer h) Laser scribing (P3) to electrically isolate the second conducting layer

[0012] FIG. 3: Flow chart for fabrication of P2’less PV (The invention)

[0013] FIG. 4: Demonstration of steps for fabrication of P2’less PV (The invention) a) Deposition of the first conducting layer on a substrate b) Laser scribing (Pl) to isolate the first conducting layer of adjacent cells c) Deposition of the charge transport layer d) Deposition of the absorber layer on top of the charge transfer layer e) Deposition of the opposite charge transport layer on the absorber layer f) Deposition of the second conducting layer on top of the opposite charge transport layer g) Laser scribing (P3) to electrically isolate the second conducting layer

[0014] FIG. 5: JV curve of the fabricated P2’less perovskite solar module

[0015] References in Figures

[0016] (1) Substrate

[0017] (2) First Conducting layer

[0018] (3) Pl: Isolation line of the first conducting layer

[0019] (4) Charge transport layer

[0020] (5) Photoabsorber layer

[0021] (6) Opposite charge transport layer

[0022] (7) P2: Interconnection zone opening of the adjacent photovoltaic cells

[0023] (8) Second conducting layer

[0024] (9) P3 : Isolation line of the second conducting layer

[0025] Detailed Description of the Invention

[0026] The invention is an interconnection method that requires no P2 scribing. In conventional PV thin-film modules, the processed P2 scribing zone is called the interconnection zone. The ohmic contact at the interconnection zone between the adjacent cells’ first and second conducting layers provides a path for current flowing from one cell to another. In this invention, the zone between the Pl and P3 is left unprocessed. This zone between each photovoltaic PV comprises reversely connected diodes. The application of reverse bias voltage after a certain value converts the reversely connected diodes to low-resistivity resistors. These resistors are the pathways for the photogenerated current in the active areas of MIMs. Adjacent cells are connected through these low-resistivity resistive paths. In especially low current-generating PV applications, this resistance can easily be tolerated as the power loss is related to the square of the current multiplied by the resistance. Thus, it does not lead to performance degradation for MIMs. As mentioned above, the main problem of having an interconnection processing is the need for excessive time to optimize its scribing or doping parameters and the need for interrupting the fabrication protocols. On that matter, the invention mainly solves four problems;

[0027] (1) Since one scribing process is removed from the fabrication protocol, it provides a shorter fabrication duration in 2 different perspectives. a. Process time, including the transfer of the fdms to different systems in possibly different locations and the P2 laser process, is avoided. b. Optimization time for P2 is avoided.

[0028] (2) Since material removal during P2 is avoided, exposure to possibly vapors or specks of toxic materials is avoided.

[0029] (3) Since the direct contact between the bottom-most contact material and the absorber layer is avoided, one of the degradation channels of the MIMs is prevented.

[0030] Overall, the fabrication of photovoltaic MIMs without P2 interconnection scribes simplifies the interconnection process and increases the MIM’s reliability and reproducibility. Figures 3 and 4 demonstrate steps to fabricate P2’less PV.

[0031] Processing starts with a substrate (1) material on which all the layers would be deposited. Typically, the substrate material could be glass, tile, steel, plastics, or a semiconductor such as Si. If the substrate material is opaque to the light spectrum of interest, then the photovoltaic device is operated in a superstrate configuration. Otherwise, if the substrate material is transparent to the same wavelength range, the photovoltaic device can operate both at substrate or superstrate configuration.

[0032] Processing starts with the deposition of the first conducting layer (2). The first conducting layer (2) material is preferably metals (E.g., Cu, Ag, Al, Au), dielectric-metal-dielectric multilayers (E.g., MoOx / Ag / MoOx), or transparent conducting oxides (E.g., indium tin oxide, fluorine tin oxide). These contact materials are to collect and transfer the photogenerated carriers (positively charged holes or negatively charged electrons).

[0033] Pl (3), the isolation line of the first conducting layer is formed by laser or mechanical (knife, shadow mask, etc.) processing, utilized to create isolated contacts. Owing to this scribe (Pl), one of the poles of the interconnected cells is electrically isolated to achieve series interconnection. In one embodiment of the invention, the charge transport layer (4) is deposited on the first conducting layer (2). The charge transport layer (4) works as a transporter of one type of charge (positive (holes) or negative (electrons)) to the contact layers. Charge transport layer (4) can be p-type or n-type materials preferably Nickel oxides (NiOx), Tin oxides (SnOx), poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), 2,2',7,7'-Tetra(N,N-di-p- tolyl)amino-9,9-spirobifluorene (Spiro-TTB), Zinc oxide (ZnOx), N2,N2,N2,N2,N7,N7,N7,N7- octakis(4-methoxyphenyl)-9,9'-spirobi[9H-fluorene]-2,2',7,7'-tetramine (Spiro-O-MeTAD), Titanium oxides (TiOx), Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), [6,6]- Phenyl-C61 -butyric acid methyl ester (PCBM), Fullerene (Ceo).

[0034] In another embodiment of the invention, the charge transport layer (4) consists of multiple layers working as a single transporting layer. Additional layers can work as a passivating, buffer, or interfacial layer, etc. These layers can preferably be exemplified as Lithium fluoride (LiF), 2,9-Dimethyl-4,7-diphenyl-l,10-phenanthroline (BCP), [6,6] -Phenyl-C61 -butyric acid methyl ester (PCBM), Tin oxides (SnOx), Phenethylammonium iodide (PEAI).

[0035] In another embodiment of the invention, no charge transport layer is deposited on the active layer. Instead, the charge transport occurs from the active layer to the first conducting layer.

[0036] The next step of the process is the deposition of the absorber layer (5), which could be any thin film including perovskites, organic absorbers, III / V group semiconductors, II / VI group semiconductors, amorphous Si, or quantum dots. The absorber layer is sensitive to light with energies equal to or larger than the absorbing material’s band gap. When the light within this range falls upon the layer (5), it produces charge carriers.

[0037] In one embodiment of the invention, the opposite charge transport layer (6) is deposited on the absorber layer (5). If the charge transport layer (4) is selected as a p-type semiconductor, then the opposite charge transport layer (6) is an n-type semiconductor material. These charge transport materials work as a transporter of one type of charge (positive (holes) or negative (electrons)) to the contact layers (2, 8).

[0038] In another embodiment of the invention, the opposite charge transport layer (4) consists of multiple layers working as a single transporting layer. Additional layers can work as passivating, buffer, or interfacial layers. These layers can preferably be exemplified as Lithium fluoride (LiF), 2,9-Dimethyl-4,7-diphenyl-l,10-phenanthroline (BCP), [6,6]-Phenyl-C61- butyric acid methyl ester (PCBM), Tin oxides (SnOx), Phenethylammonium iodide (PEAI). In another embodiment of the invention, no opposite charge transport layer is deposited on the active layer. Instead, the opposite charge transport occurs from the active layer to the second conducting layer.

[0039] In conventional PV module devices, P2 scribing is done at this step which is before the deposition of the second conductive layer (8). However, in the process of invention, no P2 scribing is needed.

[0040] The process of the invention proceeds by deposition of the second conducting layer (8). Metals, dielectric-metal-dielectric complexes, conductive metal oxides such as Indium Tin Oxide (ITO), Fluorinated Tin Oxide (FTO), Hydrogenated Indium Oxide, Indium Zinc Oxides (IZO), Aluminum-doped Zinc Oxides (AZO), Conductive organic materials such as graphene, carbon electrodes are alternative materials that can be used as second conducting layer (8). These contact materials work for the collection of photogenerated carriers produced in the absorber layer (5) which are flowing through the transport layers (4, 6).

[0041] As the last step of the process of the invention, the second conducting layer (8) is scribed so that electrical isolation of the second conducting layer (8) is achieved. This step provides P3. After that step, the series interconnection of the adjacent cells is finalized.

[0042] The P2 step is dismissed in the fabrication process of the invention. In especially low currentgenerating photovoltaic devices, high contact resistance because of the reverse-breakdown diode at the interconnection zone can be omitted. Interconnection of the adjacent cells is achieved by the zone remaining between the Pl and P3 scribes. The interconnection principles are explained above.

[0043] In a preferred embodiment, perovskite solar modules are fabricated without using P2 scribing. As an example, perovskite solar modules consisting of 4 series connected cells are fabricated, and current- voltage measurement was done under LED light illumination. The electrical performance of the perovskite photovoltaic modules under LED illumination (-1000 lux) without P2 scribing lines is demonstrated in Figure 5 and Table 1.

[0044] 1. The linear increase in Voc corresponds to the successful series connection of individual cells without any shunting losses.

[0045] 2. The fill factor (FF) parameter is the direct figure -of-merit of the series resistance in the cell or module structure. The resulting 86.3% FF in the fabricated perovskite solar module means that the module does not have any significant additional series resistance . Table 1. JV parameters of the fabricated perovskite solar module without P2 scribing lines

[0046] After application of relatively high voltages, these zones that consist of reversely connected diodes, undergo reverse breakdown. They become interconnected resistors after the breakdown and follow Ohm’s law as they transfer current. In especially low-light illuminated indoor applications where the photogenerated current is very low, these resistors enable interconnections with no significant electrical losses under operation. It is demonstrated clearly by the fill factor of the preliminary fabricated perovskite solar modules of which the current- voltage curve is given in Figure 5.

Claims

CLAIMS1. A solar module having at least two cells comprising, a. first conducting layer (2) as top electrode layer b. Pl isolation line (3) of the first conducting layer (2) c. a photoactive layer (5) d. second conducting layer (8) as bottom electrode layer e. P3 isolation line (9) of the second conducting layer (8) where there is no direct contact between first conducting layer (2) of one cell and second conducting layer (8) of adjacent cell.

2. A solar module according to Claim 1 characterized in further comprising at least one charge transport layer (4) in between the first conducting layer (2) and photoactive layer (5).

3. A solar module according to Claim 2, characterized in further comprising at least one opposite charge transport layer (6) in between photoactive layer (5) and second conducting layer (8).

4. A solar module according to Claim 2 characterized in that charge transport layer (4) is p-type or n-type material.

5. A solar module according to Claim 3 characterized in that opposite charge transport layer (6) is p-type when charge transport layer (4) is n-type material or n-type when the charge transport layer (4) is p-type material.

6. The solar module according to claim 1 wherein the photoactive layer (5) is selected from perovskites, organic absorbers, III / V group semiconductors, II / VI group semiconductors, amorphous Si, or quantum dots.

7. A solar module according to Claim 1 characterized in further comprising a substrate on which all layers (2, 5, 8) are deposited or transferred.

8. A solar module according to Claim 1, where material of the first conducting layer (2) and second conducting layer (8) is selected from metals, dielectric-metal-dielectric multilayers, conductive metal oxides, or conductive organic materials.

9. A solar module according to Claim 8, where conductive metal oxide is selected from indium tin oxide, fluorinated tin oxide, indium zinc oxides, hydrogenated indium oxide or aluminum -doped zinc oxides.

10. A solar module according to Claim 8 where conductive organic material is graphene or carbon electrodes.

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