NL2024024B1

NL2024024B1 - Transparent passivated contacts for Si solar cells

Info

Publication number: NL2024024B1
Application number: NL2024024A
Authority: NL
Inventors: Alejandro Procel Moya Paul; Yang Guangtao; Zeman Miroslav; Isabella Olindo; Mazzarella Luana
Original assignee: Univ Delft Tech
Priority date: 2019-10-16
Filing date: 2019-10-16
Publication date: 2021-06-17
Also published as: WO2021075956A1; EP4046205A1

Abstract

The present invention is in the field of a process for making solar cells, or photovoltaic (PV) cell, with transparent contacts based on a contact stack of three layers, and so— lar cells with transparent contacts, typically front and/or rear contacted solar cells. Said solar cells comprise at least one hetero junction and optionally two hetero junctions.

Description

Transparent passivated contacts for Si solar cells

FIELD OF THE INVENTION The present invention is in the field of a process for making solar cells, or photovoltaic (PV) cell, with transpar- ent contacts based on a contact stack of three layers, and so- lar cells with transparent contacts, typically front and/or rear contacted solar cells. Said solar cells comprise at least one hetero junction and optionally two hetero junctions.

BACKGROUND OF THE INVENTION A solar cell, or photovoltaic (PV) cell, is an electrical device that converts energy of light, typically sun light (hence “solar”), directly into electricity by the so-called photovoltaic effect. The solar cell may be considered a photo- electric cell, having electrical characteristics, such as cur- rent, voltage, resistance, and fill factor, which vary when exposed to light and which vary from type of cell to type.

Solar cells are described as being photovoltaic irrespec- tive of whether the source is sunlight or an artificial light. They may also be used as photo detector.

When a solar cell absorbs light it may generate either electron-hole pairs or excitons. In order to obtain an elec- trical current charge carriers of opposite types are separat- ed. The separated charge carriers are “extracted” to an exter- nal circuit, typically providing a DC-current. For practical use a DC-current may be transformed into an AC-current, e.d. by using a transformer.

Typically solar cells are grouped into an array of ele- ments. Various elements may form a panel, and various panels may form a system.

Wafer based c-Si solar cells contribute to more than 90% of the total PV market. According to recent predictions, this trend will remain for the upcoming years towards 2020 and many years beyond. Due to their simplified process, conventional c- Si solar cells dominate a large part of the market. As alter- native to the industry to improve the power to cost ratio, the silicon heterojunction approach has become increasingly at- tractive for PV industry, even though the relatively compli- cated process to deploy the proper front layers, such as a thermal conductive oxide (TCO) and an inherent low thermal budget of the cells limiting usage of existing production lines and thus result in a negligible market share so far.

A heterojunction is the interface that occurs between two layers or regions of dissimilar crystalline semiconductors.

These semiconducting materials have unequal band gaps as opposed to a homojunction.

A homojunction relates to a semiconductor in- terface formed by typically two layers of similar semiconduc- tor material, wherein these semiconductor materials have equal band gaps and typically have a different doping (either in concentration, in type, or both). A common example is a homo- junction at the interface between an n-type layer and a p-type layer, which is referred to as a p-n junction.

In heterojunc- tions advanced techniques are used to precisely control a dep- osition thickness of layers involved and to create a lattice- matched abrupt interface.

Three types of heterojunctions can be distinguished, a straddling gap, a staggered gap, and a broken gap.

A disadvantage of solar cells is that the conversion per se is not very efficient, typically, for Si-solar cells, lim- ited to some 20%. Theoretically a single p-n junction crystal- line silicon device has a maximum power efficiency of 33.75. An infinite number of layers may reach a maximum power effi- ciency of 86%. The highest ratio achieved for a solar cell per se at present is about 44%. For commercial silicon solar cells the record is about 25.6%. In view of efficiency the front contacts may be moved to a rear or back side, eliminating shaded areas.

In addition thin silicon films were applied to the wafer.

Solar cells also suffer from various imperfections, such as recombination losses, reflectance losses, heating dur- ing use, thermodynamic losses, shadow, internal resistance, such as shunt and series resistance, leakage, etc.

A qualifi- cation of performance of a solar cell is the fill factor (FF). The fill factor may be defined as a ratio of an actual maximum obtainable power to the product of the open circuit voltage and short circuit current.

It is considered to be a key param- eter in evaluating performance.

A typical advanced commercial solar cell has a fill factor > 0.75, whereas less advanced cells have a fill factor between 0.4 and 0.7. Cells with a high fill factor typically have a low equivalent series re-

sistance and a high equivalent shunt resistance; in other words less internal losses occur. Efficiency is nevertheless improving gradually, so every relatively small improvement is welcomed and of significant importance.

Typically a design of contacts may be complex or complex to manufacture, and manufacture thereof may involve surplus of material.

Solar cells with full area passivating contacts for both polarizations are now attracting industry interest. Commonly, the solar cells featuring passivating contacts are designed to decouple the carrier collection via deposited layers that can induce absorber bulk carrier separation by themselves (SHJ case) or with the support of doping region (poly-Si alloys). In both cases, doped deposited layers perform as charge col- lecting layer. If the layer is not conductive enough, the structure demands the use of TCO to support the lateral transport of the charge. Doped layers unfortunately limit the amount of generated carriers by increasing parasitic absorp- tion losses. Moreover, the use of different materials and in- terfaces make the fabrication process more complex and sensi- tive to variability. The present invention relates to an increased efficiency hetero junction solar cell and various aspects thereof and a simplified process for manufacturing the solar cell which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION The present invention relates in a first aspect to a front and/or rear contacted solar cell according to claim 1, and in a second aspect to a process for making such a solar cell according to claim 26. For some aspects of the present invention reference can be made to W02019/066648 Al, which publication and its contents are incorporated by reference. The present stack combines a high conductivity and high trans- parency for carrier selective contacts. It combines highly doped regions with donors or acceptors, typically close to a silicon bulk interface, a thin passivation layer, and a trans- parent conductive oxide (TCO) layer, with a contact, typically a metal contact. The contact stack has three layers 21,22,23,

the stack comprising a transparent conductive oxide layer 21 in contact with a chemical dielectric passivation layer 22, the chemical dielectric passivation layer in contact with a field passivation layer and/or field passivation region 23.

In the present invention, to simplify the process of solar cell fabrication, a novel and yet simple approach is disclosed for high transparent passivating contacts. Such an approach uses only TCO layer on top of a passivating layer capping a silicon absorber bulk with p+ and n+ regions at the interface.

Main advantages of invention are: {1) A simplified fabrication process: (i) solar cell pre- cursors featuring highly doped regions (field pas- sivation region) on standard processes, (ii) low cost, high throughput, and industrial standard metallization steps are applicable to the present solar cell process.

(2) Solar cells featuring high Voce are obtained, due to the full passivated contacts.

(3) Solar cells are obtained featuring high Jsc & Voce due to the high transparency of the passivating contacts.

(4) Solar cells are obtained featuring a relatively high fill factor (FF) due to the direct carrier collection supported on high conductivity of TCO.

(5) The materials and approach for increasing the cell FF (ad-vantage (4)) are feasible for both front/rear con- tacted prior art solar cell architecture and also bifa- cial solar cell architecture.

{6} FF and V.. are found to be almost insensitive to metal- lization, as TCO layers are found to perform as effi- cient carrier collection, through only one interface.

(7) For bi-facial solar cells no efficiency degradation is ex-perienced (advantage (6)), thus exhibiting a high bi-faciality factor, such as above 95%.

(8) A cost-effective TCO is enough to support charge col- lection.

{8) for IBC solar cells, the process flow is simplified.

In summary the present invention provides a simplified fabrication process wherein solar cell precursors can be finished within a couple of steps, and which is a low cost and high throughput process, using compatible industrial standard metallization steps, solar cells featuring a high Vee (>710 mV) due to the full passivated contacts, solar cells featuring a high Jse (> 39 mA/cm®) & Vee (>710 mV) due to the high transparency of the passivating contacts, solar 5 cells featuring a relatively high fill factor (FF) (>79%) due to improved transport inside a bulk, such as c-Si, and wherein the design is applicable to both a front/rear con- tacted conventional solar cell architecture, a bifacial so- lar cell architecture and for both n-type and p-type bulk material.

Thereby the present invention provides a solution to one or more of the above mentioned problems.

Advantages of the present description are detailed throughout the description. References to the figures are not limiting, and are only intended to guide the person skilled in the art through details of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates in a first aspect to front and/or rear contacted solar cell according to claim 1, and in a second aspect to a process for making such a solar cell according to claim 26.

In an exemplary embodiment of the present solar cell the field passivation layer or region may have a <400 meV activa- tion energy, such as <300 meV, and is preferably a continuous layer (apart from possible contacts).

In an exemplary embodiment of the present solar cell the field passivation material may be selected from a doped sub- region, such as by adding an acceptor or donor, such as by im- plantation, and diffusion, from a supra-region, such as lay- ers, which may be in-situ or ex-situ doped, wherein layers are provided by Epitaxial growth, Poly-Si alloys deposition, PECVD, and LT PECVD.

In an exemplary embodiment of the present solar cell in a sub-region a dopant concentration may be >5*10%%/cm?®, prefer- ably >8*102°/cm?, a junction depth may be <200 um, preferably 10-100 um, a thickness may be <500 nm, preferably 50-200 nm, and combinations thereof.

In an exemplary embodiment of the present solar cell the chemical passivation layer may comprise a wide band gap mate- rial.

In an exemplary embodiment of the present solar cell the chemical passivation layer material may be a-SiH, wherein a- SiH may comprise N, C, or O, SiOx, SixNy, AlO,, HfOx.

In an exemplary embodiment of the present solar cell the chemical passivation layer may have a thickness of 0.1-20 nm, such as 0.2-10 nm, and combinations thereof, and is preferably a continuous layer (apart from possible contacts).

In an exemplary embodiment of the present solar cell the bulk substrate material may be selected from Micro-crystalline Silicon, Multi-crystalline Silicon, Czochralski Silicon, Floating zone Silicon, Epitaxial Silicon, Ribbon Silicon, Lig- uid phase Silicon.

In an exemplary embodiment of the present solar cell the bulk substrate may be selected from n-type, p-type, intrinsic, and combinations thereof.

In an exemplary embodiment of the present solar cell the solar cell may be an IBC solar cell, and wherein the solar cell may comprise an n-doped field passivation region and a p- doped field passivation region at one side of the solar cell.

In an exemplary embodiment of the present solar cell the solar cell may be a front- and rear-contacted solar cell, and may comprise a stack of three layers at the front and at the rear.

In an exemplary embodiment of the present solar cell the solar cell may be a bifacial solar cell, and wherein at the front the field passivation region may comprise n-type dopants and wherein at the back the field passivation region may com- prise p-type dopants.

In an exemplary embodiment of the present solar cell the transparent conductive oxide may selected from zinc oxide, in- dium oxide, tin oxide, cadmium oxide, gallium oxide, doped ox- ides, such as doped with F, and combinations thereof.

In an exemplary embodiment of the present solar cell at least one contact may comprise a stack of layers, which stack comprises a layer 11,12 of > 10 nm thickness, such as an an n-doped or p-doped poly SiOx layer, a layer 13,14 of 100 nm-

5000 nm thickness, such as a n-doped or p-doped crystalline Si layer 13,14, wherein the 11,12 and layer 13,14 are both p- doped or are both n-doped, and in between said lavers a die- lectric barrier layer (15) of thickness of 0 < tgie1<2.5 mm, wherein said layers cover one and another, wherein the ratio of doping of layer 11,12/layer 13,14 at the dielectric barrier layer is > 2, preferably > 5, more preferably > 10, even more preferably > 102.

In an exemplary embodiment of the present solar cell the contact stack 18b,18f may be a carrier selective passivating contact.

In an exemplary embodiment of the present solar cell the contact 18b,18f may be transparent.

In an exemplary embodiment the present solar cell may comprise a single sided or double sided textured substrate 10.

In an exemplary embodiment the present solar cell may comprise a 5*10%-0.5*10% dopants/cm® n- or p-type doped crys- talline Si layer (13,14), wherein a doping concentration is preferably spatially constant, wherein n-type dopants may be selected from P, As, Bi, Sb and Li, and wherein p-type dopants may be selected from B, Ga, and In.

In an exemplary embodiment the present solar cell may comprise a dielectric passivation layer or dielectric pas- sivation stack 17 on the cell.

In an exemplary embodiment the present solar cell may comprise a 10-1017 dopants/cm® n- or p-type doped substrate

10.

In an exemplary embodiment the present solar cell may comprise at least one of a metal layer on a back side 18b}, metal contacts on a front side 18f and/or on a back side 18b, and a transparent conductive layer 19.

In an exemplary embodiment the present solar cell may comprise at least one dielectric barrier layer 15 each inde- pendently of thickness of 0.1 nm-1.4 nm, wherein the dielec- tric barrier layer 15 independently may comprise at least one material selected from Si0:, HfO:z, and W:0s.

In an exemplary embodiment of the present solar cell the material of the transparent conductive layer 19 may be select- ed from ITO, ICH, ZnO or doped ZnO, and IWO.

In an exemplary embodiment of the present solar cell a thickness of the transparent conductive layer 19 may be <100 nm, such as 10-40 nm.

In an exemplary embodiment of the present solar cell the refractive index of the transparent conductive layer 19 may be <2.2.

In an exemplary embodiment of the present solar cell in the stack of layers, the layer 11,12, such as the n-doped or p-doped poly SiOx layer, the layer 13,14, such as the n-doped or p-doped crystalline Si layer, and the dielectric barrier layer 15 may be each independently in full contact with one and another over an area of >50% of a surface of the largest of two contacting surfaces.

In an exemplary embodiment the present solar cell A may comprise a stack of a metal layer 18b, an n-type doped poly- SiOx layer 12, a dielectric layer 15, an n-type-doped crystal- line Si-layer 14, a Si-substrate 10, a p-type-doped crystal- line Si-layer 13, a dielectric layer 15, a p-type doped poly- SiOx layer 11, a dielectric layer 17, and metal contacts 18f penetrating through the dielectric layer 17 and contacting the p-type doped poly-SiOx layer 11.

In an exemplary embodiment the present solar cell B may comprise a stack of a metal layer 18b, a p-type doped poly- SiOx layer 12, a dielectric layer 15, a p-type-doped crystal- line Si-layer 14, a Si-substrate 10, an n-type-doped crystal- line Si-layer 13, a dielectric layer 15, an n-type doped poly- SiOx layer 11, a dielectric layer 17, and metal contacts 18f penetrating through the dielectric layer 17 and contacting the n-type doped poly-SiOx layer 11.

In an exemplary embodiment the present solar cell C may comprise a stack of a metal layer 18b, an n-type doped poly- SiOx layer 12, a dielectric layer 15, an n-type-doped crystal- line Si-layer 14, a Si-substrate 10, a p-type-doped crystal- line Si-layer 13, a dielectric layer 15, a p-type doped poly- SiOx layer 11, a transparent conductive oxide layer 19, and metal contacts 18f penetrating through the transparent conduc- tive oxide layer 19 and contacting the p-type doped poly-SiOx layer 11.

In an exemplary embodiment the present solar cell D may comprise a stack of a metal layer 18b, a p-type doped poly- SiOx layer 12, a dielectric layer 15, a p-type-doped crystal- line Si-layer 14, a Si-substrate 10, an n-type-doped crystal- line Si-layer 13, a dielectric layer 15, an n-type doped poly- SiOx layer 11, a transparent conductive oxide layer 19, and metal contacts 18f penetrating through the transparent conduc- tive oxide layer 19 and contacting the n-type doped poly-5i0x layer 11. In an exemplary embodiment the present solar cell E may comprise a stack of a metal layer 18b, a transparent conduc- tive oxide layer 19, an n-type doped poly-SiOx layer 12, a di- electric layer 15, an n-type-doped crystalline Si-layer 14, a Si-substrate 10, a p-type-doped crystalline Si-layer 13, a di- electric layer 15, a p-type doped poly-SiO0x layer 11, a trans- parent conductive oxide layer 19, and metal contacts 18f pene- trating through the transparent conductive oxide layer 19 and contacting the p-type doped poly-SiO0x layer 11. In an exemplary embodiment the present solar cell F may comprise a stack of a metal layer 18b, a transparent conduc- tive oxide layer 19, a p-type doped poly-SiOx layer 12, a die- lectric layer 15, a p-type-doped crystalline Si-layer 14, a Si-substrate 10, an n-type-doped crystalline Si-layer 13, a dielectric layer 15, an n-type doped poly-SiO0x layer 11, a transparent conductive oxide layer 19, and metal contacts 18f penetrating through the transparent conductive oxide layer 19 and contacting the n-type doped poly-SiOx layer 11. In an exemplary embodiment the present solar cell G may comprise a stack of a dielectric layer 17, metal contacts 18b penetrating through the dielectric layer 17 and contacting an n-type doped poly-SiOx layer 12, an n-type doped poly-SiOx layer 12, a dielectric layer 15, an n-type-doped crystalline Si-layer 14, a Si-substrate 10, a p-type-doped crystalline Si- layer 13, a dielectric layer 15, a p-type doped poly-5i0Ox lay- er 11, a dielectric layer 17, and metal contacts 18f penetrat- ing through the dielectric layer 17 and contacting the p-type doped poly-Si0x layer 11. In an exemplary embodiment the present solar cell H may comprise a stack of a dielectric layer 17, metal contacts 18b penetrating through the dielectric layer 17 and contacting an p-type doped poly-SiOx layer 12, a p-type doped poly-5i0Ox lay- er 12, a dielectric layer 15, a p-type-doped crystalline Si- layer 14, a Si-substrate 10, an n-type-doped crystalline Si- layer 13, a dielectric layer 15, an n-type doped poly-SiO0x layer 11, a dielectric layer 17, and metal contacts 18f pene- trating through the dielectric layer 17 and contacting the n- type doped poly-SiO0x layer 11.

In an exemplary embodiment the present solar cell may comprise at least one textured surface 20, wherein the tex- tured surface 20 may have an aspect ratio height:depth of a Textured structure of 2-10. In an exemplary embodiment the present solar cell may have n-doped or p-doped poly SiOx layer 11,12 independently of 10 nm- 5000 nm thickness, and may comprise 1*1012-5*x102: n- or p-type dopants/cm?, wherein a doping profile is preferably substantially constant over the thickness of the layer 11,12, wherein n-type dopants may be selected from P, As, Bi, Sb and Li, and wherein p-type dopants may be selected from B, Ga, and In.

In an exemplary embodiment the present solar cell may comprise at least one dielectric layer 17 each independently of thickness of 10 nm-2000 nm, wherein the dielectric layer 17 independently may comprise at least one material selected from SiNs, AlOyx, S5i0x, a n-type or p-type doped or un-doped trans- parent conductive oxide.

In an exemplary embodiment of the present solar cell the metal of the metal layers 18b and metal contacts 18f inde- pendently may comprise at least one of Cu, Al, W, Ti, Ni, and Ag, wherein a thickness of said metal 18b,18f may be 200-5000 nm.

In an exemplary embodiment of the present method the n- doped or p-doped poly SiOx layer 11,12 may be provided by PECVD, or LPCVD, wherein dopants may be constantly provided during deposition.

In an exemplary embodiment of the present method metal contacts and/or metal layers 18b,18f may be provided by metal deposition and lift off of non-contact areas, screen printing, and electrical plating.

In an exemplary embodiment of the present method dopants in the poly SiOx layer 11,12 may be activated.

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention.

To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY OF FIGURES Figures 1-13 show a schematic representation of examples of the present solar cell.

DETAILED DESCRIPTION OF FIGURES 100 solar cell 10 substrate 11 p-doped poly silicon oxide 12 n-doped poly silicon oxide 13 p-doped crystalline silicon 14 n-doped crystalline silicon 15 thin dielectric layer 16 antireflective coating layer 17 dielectric layer or stack of layers 18b back side metal contacts or back side metal layer 18f front side metal contacts or front side metal layer 19 transparent conductive oxide layer 20 textured surface 21 transparent conductive oxide layer 22 chemical dielectric passivation layer 23 field passivation layer and/or field passivation region The figures are further detailed in the description of the experiments below.

Figure 1 shows a contact stack with Si based bulk 10, a field passivation region 23, a chemical passivation layer 22, a TCO 21, and a metal contact 18b or 18f.

Figure 2 shows a front and rear contacted, monofacial, so- lar cell with bulk silicon 10, with two stacks with a field passivation region 23, a chemical passivation layer 22, a TCO 21, and a metal contact 18b or 18f, at either side.

Figure 3 shows an IBC monofacial solar cell with bulk sil- icon 10, with two stacks (left and right) with a field pas- sivation region 23, a chemical passivation layer 22, a TCO 21, and a metal contact 18b, at either side, wherein the right field passivation region 23p is positively charged and wherein the left field passivation region 23n is negatively charged. Further an antireflective coating layer 19 is provided.

Figure 4 shows an IBC bifacial solar cell with bulk sili- con 10, with two stacks (left and right) with a field pas- sivation region 23, a chemical passivation layer 22, a TCO 21, and a metal contact 18b, at either side, wherein the right field passivation region 23p is positively charged and wherein the left field passivation region 23n is negatively charged. Further an antireflective coating layer 19 is provided.

Figure 5 shows a front and rear contacted, bifacial, solar cell with bulk silicon 10, with two stacks with a field pas- sivation region 23, a chemical passivation layer 22, a TCO 21, and a metal contact 18b or 18f, at either side, wherein the top field passivation region 23p is positively charged and wherein the bottom field passivation region 23n is negatively charged.

In figures 6-11 shows front and rear contacted solar cells, indicated with type A-F. Figures 12-13 show similar designs as above for a bifacial solar cell.

EXAMPLES/EXPERIMENTS Results of the present solar cells are found to be good. For instance, an excellent surface passivation is achieved. The Voc and fill factor FF of the cells are found to be sensitive to the transparent conductive oxide appli- cation process. For the n-type solar cell Jo of 3 fA/cm? and implied a Voc as high as 740 mV, the p-type solar cell Jo of 23 fA/cm? and implied Vee as high as 700 mV, is obtained.

The calculated solar cell presents an efficiency of 24%, a FF up to 83.5%, and Jsc up to 41 mA/cm? with a double side textured surface.

The invention although described in detailed explanato- ry context may be best understood in conjunction with the accompanying figures. It should be appreciated that for commercial application it may be preferable to use one or more variations of the pre- sent system, which would similar be to the ones disclosed in the present application and are within the spirit of the in- vention. The next section is provided in order to support the search. The section thereafter relates to a translation there- of.

1. Front and/or rear contacted solar cell (100) comprising at least one hetero junction, a bulk substrate (10), a contact stack of three layers (21,22,23), the stack com- prising a transparent conductive oxide layer (21) in con- tact with a chemical dielectric passivation layer (22), the chemical dielectric passivation layer in contact with a field passivation layer and/or region (23), wherein the transparent conductive oxide layer (21) is at an outside of the solar cell, wherein the field passivation layer/region (22) comprises n-type or p-type dopants, wherein the transparent conductive oxide layer (21) has a thickness of > 25 nm, a carrier concentration of >5*¥10%%/cm3, and is preferably not-textured, and on the transparent conductive oxide layer (21) at least one front and/or back contact (18b,18f), preferably a met- al contact.

2. Solar cell according to embodiment 1, wherein the field passivation layer or region has a <400 meV activation en- ergy, and is preferably a continuous layer.

3. Solar cell according to any of embodiments 1-2, wherein the field passivation material is selected from a doped sub-region, such as by adding an acceptor or donor, such as by implantation, and diffusion, from a supra-region, such as layers, which may be in-situ or ex-situ doped, wherein layers are provided by Epitaxial growth, Poly-Si alloys deposition, PECVD, and LT PECVD, and/or wherein in a sub-region a dopant concentration is >5*101%/cm®, a junc- tion depth is < 200 um, a thickness is < 500 nm, and com- binations thereof.

4. Solar cell according to any of embodiments 1-3, wherein the chemical passivation layer comprises a wide band gap material, and/or wherein the chemical passivation layer material is a-SiH, wherein a-SiH may comprise N, C, or O, SiOx, SisNy, AlOyx, HfOx, and/or wherein the chemical pas- sivation layer has a thickness of 0.1-20 nm, and combina- tions thereof, and is preferably a continuous layer.

5. Solar cell according to any of embodiments 1-4, wherein the bulk substrate material is selected from Micro- crystalline Silicon, Multi-crystalline Silicon, Czochralski Silicon, Floating zone Silicon, Epitaxial Silicon, Ribbon Silicon, and Lig- uid phase Silicon, and/or wherein the bulk substrate is selected from n-type, p-type, intrinsic, and combinations thereof.

6. Solar cell according to any of embodiments 1-5, wherein the solar cell is an IBC solar cell, and wherein the solar cell comprises an n-doped field passivation region and a p-doped field passivation region at one side of the solar cell.

7. Solar cell according to any of embodiments 1-5, wherein the solar cell is a front- and rear-contacted solar cell, and comprises a stack of three layers at the front and at the rear.

8. Solar cell according to embodiment 7, wherein the solar cell is a bifacial solar cell, and wherein at the front the field passivation region comprises n-type dopants and wherein at the back the field passivation region comprises p-type dopants.

9. Solar cell according to any of embodiments 1-8, wherein the transparent conductive oxide is selected from zinc ox- ide, indium oxide, tin oxide, cadmium oxide, gallium ox- ide, doped oxides, such as doped with F, and combinations thereof.

10. Solar cell according to any of embodiments 1-9, wherein at least one contact comprises a stack of layers, which stack comprises a layer (11,12) of > 10 nm thickness, such as an n-doped or p-doped poly SiOx layer (11,12), a layer (13,14) of 100 nm-5000 nm thickness, such as a n-doped or p-doped crystalline Si layer, wherein the layer (11,12) and layer (13,14) are both p-doped or are both n-doped, and in between said layers a dielectric barrier layer (15) of thickness of 0 < tsie1<2.5 nm, wherein said layers cover one and another, wherein the ratio of doping of layer (11,12) /layer 13,14) at the dielectric barrier layer is > 2, preferably > 5, more preferably > 10, even more prefer- ably > 102.

11. Solar cell according to any of embodiments 1-10, wherein the contact stack (18b,18f) is a carrier selective passiv- ating contact.

12. Solar cell according to any of embodiments 1-11, wherein the contact (18b,18f) is transparent.

13. Solar cell according to any of embodiments 1-12, compris- ing a single sided or double sided textured substrate (10).

14. Solar cell according to any of embodiments 1-13, compris- ing a 5*1014-0.5%10%° dopants/cm? n- or p-type doped crys- talline Si layer (13,14), wherein a doping concentration is preferably spatially constant, wherein n-type dopants are selected from P, As, Bi, Sb and Li, and wherein p-type dopants are selected from B, Ga, and In.

15. Solar cell according to any of embodiments 1-14, compris- ing a dielectric passivation layer or dielectric pas- sivation stack (17) on the cell.

16. Solar cell according to any of embodiments 1-15, compris- ing a 10%-10%7 dopants/cm® n- or p-type doped substrate (10).

17. Solar cell according to any of embodiments 1-16, compris- ing at least one of a metal layer on a back side (18b), metal contacts on a front side (18f) and/or on a back side {18b), and a transparent conductive layer (19).

18. Solar cell according to any of embodiments 1-17, compris- ing at least one dielectric barrier layer (15) each inde- pendently of thickness of 0.1 nm-1.4 nm,

wherein the dielectric barrier layer (15) independently comprises at least one material selected from Si0z, HfO:z, and W20s.

19. Solar cell according to any of embodiments 1-18, wherein the material of the transparent conductive layer (19)is selected from ITO, ICH, Zn0 or doped Zn0, IFO, and IWO, and/or wherein a thickness of the transparent conductive layer (19) is <100 nm, and/or wherein the refractive index is «2.2.

20. Solar cell according to any of embodiments 1-19, wherein in the stack of layers, the layer (11,12), such as the n- doped or p-doped poly SiOx layer, the n-doped or p-doped layer (13,14), such as the n-doped or p-doped crystalline Si layer, and the dielectric barrier layer (15) are each independently in full contact with one and another over an area of >50% of a surface of the largest of two contacting surfaces.

21. Solar cell according to any of embodiments 1-20, (A) comprising a stack of a metal layer (18b), an n-type doped poly-Si0x layer (12), a dielectric layer (15), an n-type-doped crystalline Si-layer (14), a Si- substrate (10), a p-type-doped crystalline Si-layer (13), a dielectric layer (15), a p-type doped poly- SiOx layer (11), a dielectric layer (17), and metal contacts (18f) penetrating through the dielectric lay- er (17) and contacting the p-type doped poly-SiO0x lay- er (11), or (B) comprising a stack of a metal layer (18b), a p-type doped poly-Si0x layer (12), a dielectric layer (15), a p-type-doped crystalline Si-layer (14), a Si-substrate (10), an n-type-doped crystalline Si-layer (13), a di- electric layer (15), an n-type doped poly-3i0Ox layer (11), a dielectric layer (17), and metal contacts (18f) penetrating through the dielectric layer (17) and contacting the n-type doped poly-SiOx layer (11), or (C) comprising a stack of a metal layer (18b), an n-type doped poly-Si0Ox layer (12), a dielectric layer (15), an n-type-doped crystalline Si-layer (14), a Si-

substrate (10), a p-type-doped crystalline Si-layer (13), a dielectric layer (15), a p-type doped poly- SiOx layer (11), a transparent conductive oxide layer (19), and metal contacts (18f) penetrating through the transparent conductive oxide layer (19) and contacting the p-type doped poly-SiOx layer (11), or (D) comprising a stack of a metal layer (18b), a p-type doped poly-SiOx layer (12), a dielectric layer (15), a p-type-doped crystalline Si-layer (14), a Si-substrate (10), an n-type-doped crystalline Si-layer (13), a di- electric layer (15), an n-type doped poly-SiO0x layer (11), a transparent conductive oxide layer (19), and metal contacts (18f) penetrating through the transpar- ent conductive oxide layer (19) and contacting the n- type doped poly-SiOx layer (11), or (BE) comprising a stack of a metal layer (18b), a transpar- ent conductive oxide layer (19), an n-type doped poly- Siox layer (12), a dielectric layer (15), an n-type- doped crystalline Si-layer (14), a Si-substrate (10), a p-type-doped crystalline Si-layer (13), a dielectric layer (15), a p-type doped poly-SiOx layer (11), a transparent conductive oxide layer (12), and metal contacts (18f) penetrating through the transparent conductive oxide layer (19) and contacting the p-type doped poly-Si0Ox layer (11), or (F) comprising a stack of a metal layer (18b), a transpar- ent conductive oxide layer (19), a p-type doped poly- SiOx layer (12), a dielectric layer (15), a p-type- doped crystalline Si-layer (14), a Si-substrate (10), an n-type-doped crystalline Si-layer (13), a dielec- tric layer (15), an n-type doped poly-Si0x layer (11), a transparent conductive oxide layer (19), and metal contacts (18f) penetrating through the transparent conductive oxide layer (19) and contacting the n-type doped poly-SiOx layer (11), or {(G) comprising a stack of a dielectric layer (17), metal contacts (18b) penetrating through the dielectric lay- er (17) and contacting an n-type doped poly-Si0x layer (12), an n-type doped poly-SiOx layer {12}, a dielec-

tric layer (15), an n-type-doped crystalline Si-layer (14), a Si-substrate (10), a p-type-doped crystalline Si-layer (13), a dielectric layer (15), a p-type doped poly-5i0x layer (11), a dielectric layer (17), and metal contacts (18f) penetrating through the dielec- tric layer (17) and contacting the p-type doped poly- SiOx layer (11), or (H) comprising a stack of a dielectric layer (17), metal contacts (18b) penetrating through the dielectric lay- er (17) and contacting an p-type doped poly-SiOx layer {12), a p-type doped poly-SiOx layer (12), a dielec- tric layer (15), a p-type-doped crystalline Si-layer (14), a Si-substrate (10), an n-type-doped crystalline Si-layer (13), a dielectric layer (15), an n-type doped poly-Si0x layer (11), a dielectric layer (17), and metal contacts (18f) penetrating through the die- lectric layer (17) and contacting the n-type doped poly-Si0x layer (11).

22. Solar cell according to any of embodiments 1-21, compris- ing at least one textured surface (20), wherein the tex- tured surface (20) has an aspect ratio (height:depth of a textured structure) of 2-10.

23. Solar cell according to any of embodiments 1-22, having n- doped or p-doped poly SiOx layer (11,12) independently of 10 nm- 5000 nm thickness, and comprising 1*1049-5*102 n- or p-type dopants/cm?, wherein a doping profile is preferably substantially constant over the thickness of the layer (11,12), wherein n-type dopants are selected from P, As, Bi, Sb and Li, wherein p-type dopants are selected from B, Ga, and In.

24, Solar cell according to any of embodiments 1-23, compris- ing at least one dielectric layer (17) each independently of thickness of 10 nm-2000 nm, wherein the dielectric layer (17) independently comprises at least one material selected from SiN,, AlO:, Si0x, a n- type or p-type doped or un-doped transparent conductive oxide.

25. Solar cell according to any of embodiments 1-24, wherein the metal of the metal layers (18b} and metal contacts (18f) independently comprises at least one of Cu, Al, W, Ti, Ni, and Ag, wherein a thickness of said metal (18b,18f) is 200-5000 nm.

26. Method of producing a solar cell according to any of em- bodiments 1-25 comprising at least one of providing a silicon substrate (10), texturing a rear and/or front substrate surface (10), doping a front side (13,14), doping a rear side (13,14), annealing said doped sides (13,14) at a temperature of less than 1000 °C during a sufficient period of time, providing a 0<tagiei<2.5 nm thick dielectric layer (15) on the doped front side and/or doped rear side, providing n-doped or p-doped poly SiOx layer (11,12) of > 10 nm thickness on the dielectric layer (15), wherein the ratio of doping of poly SiOx:crystalline Si at the dielec- tric barrier layer is > 2, providing at least one dielectric layer (17) on the poly SiOx layer (11,12), and providing a metal layer (18b) and/or metal contacts (18f) at a rear and front side being in electrical contact with the n-doped or p-doped poly SiOx layer (11,12), re- spectively.

27. Method according to embodiment 26, wherein the n-doped or p-doped poly SiOx layer (11,12) is provided by PECVD, or LPCVD, wherein dopants are constantly provided during dep- osition.

28. Method according to embodiments 26 or 27, wherein metal contacts and/or metal layers (18b,18f) are provided by metal deposition and lift off of non-contact areas, screen printing, and electrical plating.

29. Method according to any of embodiments 26-28, wherein do- pants in the poly SiOx layer (11,12) are activated.

Claims

CONCLUSIONS

A front and/or rear-contacted solar cell (100) comprising at least one heterojunction, a bulk substrate (10), a three-layer contact stack (21, 22, 23), the stack comprising a transparent conductive oxide layer (21) comprises in contact with a chemical dielectric passivation layer (22), the chemical dielectric passivation layer in contact with a field passivation layer and/or region (23), wherein the transparent conductive oxide layer (21) is on the outside of the solar cell wherein the field passivation layer/region (22) comprises dopants of n-type or p-type, wherein the transparent conductive oxide layer (21) has a thickness of >25 nm, a carrier concentration of >5*10%% /cm ® , and preferably has no texture, and on the transparent conductive oxide layer (21) at least one front and/or rear contact (18b, 18f), preferably a metal contact.

The solar cell of claim 1, wherein the field passivation layer or region has a <400 meV activation energy, and is preferably a continuous layer.

The solar cell of any one of claims 1-2, wherein the field passivation material is selected from a doped sub-region, such as by adding an acceptor or donor, such as by implantation and diffusion, of a supra region, such as layers , which may be doped in situ or ex-situ, wherein layers are provided by Epitaxial Growth, Poly-Si Alloy Deposition, PECVD, and LT PECVD, and/or wherein in a subregion a doping concentration is > 5*10% %/cm ® , a junction depth is <200 µm, a thickness is <500 nm, and combinations thereof.

The solar cell of any one of claims 1 to 3, wherein the chemical passivation layer comprises a wide bandgap material, and/or wherein the chemical passivation layer material is a-SiH, wherein a-SiH is N, C, or O may include SiO, SiNy, AlO 3 , HfOx, and/or wherein the chemical passivation layer has a thickness of 0.1-20 nm, and combinations thereof, and is preferably a continuous layer.

The solar cell of any one of claims 1-4, wherein the bulk substrate material is selected from microcrystalline silicon, multicrystalline silicon, Czochralski silicon, floating zone silicon, epitaxial silicon, ribbon silicon, and liquid phase silicon, and/or wherein the bulk substrate is selected from n-type, p-type, intrinsic, and combinations thereof.

The solar cell of any one of claims 1-5, wherein the solar cell is an IBC solar cell, and wherein the solar cell comprises an n-doped field passivation region and a p-doped field passivation region on one side of the solar cell.

The solar cell of any one of claims 1 to 5, wherein the solar cell is a front- and rear-contacted solar cell, and comprises a stack of three layers at the front and at the back.

The solar cell of claim 7, wherein the solar cell is a bifacial solar cell, and wherein at the front the field passivation region comprises n-type dopants, and at the rear the field passivation region comprises p-type dopants.

The solar cell of any one of claims 1-8, wherein the transparent conductive oxide is selected from zinc oxide, indium oxide, tin oxide, cadmium oxide, gallium oxide, doped oxides such as doped with F, and combinations thereof.

A solar cell according to any one of claims 1-9, wherein at least one contact comprises a stack of layers, which stack has a layer (11,12) with a thickness of > 10 nm, such as an n-doped or p-doped poly SiOx layer (11.12), a layer (13.14) with a thickness of 100 nm-5000 nm, such as an n-doped or p-doped crystalline Si layer, wherein the layer (11,12) and layer ( 13,14) are both p-doped or both are n-doped, and between said layers a dielectric barrier layer (15) having a thickness of 0<tg I<2.5 nm, said layers covering each other, the ratio of doping of layer (11,12)/layer 13,14) at the dielectric barrier layer is >2, preferably >5, more preferably >10, even more preferably >102,

The solar cell of any one of claims 1-10, wherein the contact stack (18b, 18f) is a carrier-selective passivating contact.

The solar cell of any one of claims 1-11, wherein the contact (18b, 18f) is transparent.

A solar cell according to any one of claims 1-12, comprising a single-sided or double-sided structured substrate (10).

A solar cell according to any one of claims 1-13 comprising a crystalline Si layer (13,14) doped with 5*10+4-0.5*1014° dopants/cm® n- or p-type crystalline Si layer (13,14 ), wherein a dopant concentration is preferably spatially constant, wherein n-type dopants are selected from P, As, Bi, Sb and Li, and wherein p-type dopants are selected from B, Ga and In.

A solar cell according to any one of claims 1-14, comprising a dielectric passivation layer or dielectric passivation stack (17) on the cell.

A solar cell according to any one of claims 1-15, comprising a doped substrate (10) with 10-1017 dopant/cmò of n- or p-type.

A solar cell according to any one of claims 1-16, comprising at least one of a metal layer on a back side (18b), metal contacts on a front side (18f) and/or on a back side (18b), and a transparent conductive layer (19).

A solar cell according to any one of claims 1-17, comprising at least one dielectric barrier layer (15) each independently having a thickness of 0.1nm - 1.4mm, wherein the dielectric barrier layer (15) is independent of comprises at least one material selected from SiO 2 , HfO 2 and W 2 O 5 .

A solar cell according to any one of claims 1-18, wherein the material of the transparent conductive layer (19) is selected from ITO, ICH, ZnO, or doped ZnO, IFO, and IWO, and/or wherein a thickness of the transparent conductive layer (19) is <100 nm, and/or wherein the refractive index is <2.2.

A solar cell according to any one of claims 1-19, wherein in the stack of layers the layer (11,12), such as the n-doped or p-doped polySiO: layer, the n-doped or p-doped layer ( 13, 14), such as the n-doped or p-doped crystal

line Si layer, and the dielectric barrier layer (15) are each independently in full contact with each other over an area of >50% of an area of the greater of two contact areas.

A solar cell according to any one of claims 1 to 20, (A) comprising a stack of a metal layer (18b), an n-type doped poly-SiOx layer (12), a dielectric layer (15), an n-type doped crystalline Si layer (14), a Si substrate (10), a p-type doped crystalline Si layer (13), a dielectric layer (15), a p-type doped poly-SiOr layer (11), a dielectric layer (17) and metal contacts (18f) penetrate through the dielectric layer (17) and come into contact with the doped p-type poly-SiO Ox layer (11), or (B) comprising a stack of a metal layer (18b), a p-type doped poly-SiOx layer (12), a dielectric layer (15), a p-type doped crystalline Si layer {14), a Si substrate (10), a n-type doped crystalline Si layer (13), a dielectric layer (15), an n-type doped poly-SiO: layer (11), a dielectric layer (17) and metal contacts (18f) penetrate through the dielectric low (17) and come into contact with the ge n-type doped poly-SiOrx layer (11), or (C) comprising a stack of a metal layer (18b), an n-type doped poly-SiO: layer (12), a dielectric layer (15), an n-type doped crystalline Si layer (14), a Si substrate (10), a p-type doped crystalline Si layer (13), a dielectric layer (15), a p-type doped poly-SiOx layer (11), a transparent conductive oxide layer (19), and metal contacts (18f) penetrating through the transparent conductive oxide layer (19) and contacting the doped poly-SiOx layer (11) of the p- type, or (D} comprising a stack of a metal layer (18b), a p-type doped poly-SiO: layer (12}, a dielectric layer (15), a p-type doped crystalline Si layer (14) , an Si substrate (10), an n-type doped crystalline Si layer (13), a dielectric layer (15), an n-type doped poly-S5Ox layer (11), a transparent conductive oxide layer (19), and metal contacts (18f) passing through the transparent yellow penetrating the same oxide layer (19) and contacting the doped n-type poly-SiOx layer (11), or (E) comprising a stack of a metal layer (18b), a transparent conductive oxide layer (19), an n-type doped poly-SiO: layer (12), a dielectric layer (15), an n-type doped crystalline Si layer (14), a Si substrate (10), a p-type doped crystalline Si layer (13), a dielectric layer (15), a p-type doped poly-120Ox layer (11), a transparent conductive oxide layer (19) and metal contacts (18f) passing through the transparent conductive oxide layer (19) penetrate and contact the doped p-type polySiOx layer (11), or (F) comprising a stack of a metal layer (18b), a transparent conductive oxide layer (19), a p- type doped poly-SiO: layer {12}, a dielectric layer (15), a p-type doped crystalline Si layer (14), a Si substrate (10), an n-type doped crystalline Si layer (13), a dielectric layer (1 5), an n-type doped poly-SiOO layer (11), a transparent conductive oxide layer (19) and metal contacts (18f) penetrating through the transparent conductive oxide layer (19) and contacting the doped poly-SiOx n-type layer {11), or (G) comprising a stack of a dielectric layer (17), metal contacts (18b) penetrating through the dielectric layer (17) and making contact with a doped poly-SiO:- n-type layer (12), an n-type doped poly-SiO:- layer (12), a dielectric layer (15), an n-type doped crystalline Si layer (14), a Si substrate (10), a p-type doped crystalline Si layer (13), a dielectric layer (15), a p-type doped poly-SiOO layer (11), a dielectric layer (17) and metal contacts (18f) penetrating through the dielectric layer (17) and contacting the p-type doped poly-SiO: layer (11), or (H) comprising a stack of a dielectric layer (17), metal contacts (18k) passing through the dielectric penetrating and contacting a p-type doped poly-SiO: layer (12), a p-type doped poly-SiOx layer (12), a dielectric layer (15), a p - type-doped crystalline Si layer (14), an Si substrate (10), an n-type doped crystalline Si layer (13), a dielectric layer (15), an n-type doped poly- SiOrx layer (11), a dielectric layer (17) and metal contacts (18f) penetrating through the dielectric layer (17) and contacting the n-type doped polySiOx layer {11).

The solar cell of any one of claims 1-21, comprising at least one textured surface (20), wherein the textured surface (20) has an aspect ratio (height:depth of a textured structure) of 2-10.

A solar cell according to any one of claims 1 to 22, independently comprising an n-doped or p-doped polySiO: layer (11,12) having a thickness of 10 nm - 5000 nm, and comprising 1*10:5 -5*1022 n- or p-type dopants/cm 2 , wherein a doping profile is preferably substantially constant over the thickness of the layer (11,12), wherein n-type dopants are selected from P, As, Bi, Sb and Li, wherein p-type dopants are selected from B, Ga and In.

A solar cell according to any one of claims 1 to 23, comprising at least one dielectric layer (17) each independently having a thickness of 10 nm-2000 nm, wherein the dielectric layer (17) independently comprises at least one material selected from SiN 3 , AlO 2 , SiO x , a doped or undoped transparent conducting oxide of the n-type or p-type.

The solar cell of any one of claims 1 to 24, wherein the metal of the metal layers (18b) and metal contacts (18f) independently comprises at least one of Cu, Al, W, Ti, Ni and Ag,

wherein a thickness of said metal (18b, 18f) is 200-5000 nm.

A method of producing a solar cell according to any one of claims 1-16, comprising at least one of providing a silicon substrate (10), structuring a back and/or front substrate surface (10), doping of a face (13,14), doping a back (13,14), annealing said doped sides (13.14) at a temperature of less than 1000°C for a sufficient period of time, providing a 0 <taieir<2.5 nm thick dielectric layer (15) on the doped front and/or doped back, providing n-doped or p-doped poly Si-Oz layer (11,12) with a thickness of > 10 nm on the dielectric layer (15), wherein the ratio of doping of polySiOx:crystalline Si on the dielectric barrier layer is >2, providing at least one dielectric layer (17) on the polySiOx layer (11,12), and providing a metal layer (18b) and/or metal contacts (18f) on a back and front ijde which are in electrical contact with the n-doped and p-doped polySiO: layer (11,12), respectively.

The method of claim 26, wherein the n-doped or p-doped polySiOx layer (11, 12) is provided by PECVD, or LPCVD, wherein dopants are constantly provided during deposition.

A method according to claim 26 or 27, wherein metal contacts and/or metal layers (18b, 18f) are provided by metal deposition and rising of non-contact areas, screen printing, and electroplating.

A method according to any one of claims 26-28, wherein dopants are activated in the polySiOx layer (11,12).