WO2013014181A1 - Thin-film solar cell - Google Patents

Abstract

The invention relates to a thin-film solar cell (10, 20, 30, 40) comprising a carrier substrate (11, 21, 31, 41), particularly a glass substrate, and a radiation-absorbing photoelectric active layer (17, 27, 37, 47) arranged on the carrier substrate, said layer particularly consisting of a semiconductor material or an organic material having a photovoltaic effect, as well as a conductive layer (15a, 25a, 35a, 45a) arranged between the carrier substrate and the active layer, for electrical connection of the active layer, wherein an amorphous and/or microcrystalline stabilization layer (13, 23, 33, 43) is provided between the carrier substrate and the conductive layer in order to prevent an ion drift and/or diffusion out of the conductive layer at its interface with the carrier substrate when a DC voltage of over ±50 V with respect to ground is applied.

Description

 Description title

Thin film solar cell

The invention relates to a thin-film solar cell comprising a carrier substrate, in particular a glass substrate, and a radiation-absorbing photoelectric active layer arranged on the carrier substrate, in particular of a semiconductor material or an organic material having a photovoltaic effect, and a conductive layer arranged between the carrier substrate and the active layer electrical connection of the active layer.

PRIOR ART Thin-film solar modules are usually operated serially connected in a string. At least two modules are connected in series. This adds up the electrical potential of the interconnected modules during operation.

Transparent conductive layers (TCO) are used to remove the generated photocurrent from the solar cell and are applied to the solar and optionally on the back of the absorbent material (hereinafter "active layer") .This also increases the series connection of the modules in the string electrical potential at the TCOs towards the environment (ground, stand, etc.) In the long term, high positive or negative voltages, also in connection with heat and humidity, can lead to damage to the solar cell and reduced power output.

The literature describes z. B. Na + ion drift in the glass by negative voltage to the interface to ZnO (also LPCVD-ZnO). As a result, the transported sodium ions react with ZnO under the influence of H20, forming elemental Zn, which eventually reduces the optical and electrical quality of the layer [CR. Osterwald et al., Solar Energy Materials & Solar Cells 79 (2003) 21-33], [KW Jansen et al. Thin Solid Films 423 (2003) 153-160].

Previous methods for avoiding the TCO damage to the module periphery are structurally complex and difficult to put into practice, since a high degree of flexibility is often required in the uprising systems (eg on-roof systems or building-integrated systems).

DISCLOSURE OF THE INVENTION The invention is a thin-film solar cell with the features of

Proposed claim 1. Advantageous developments of the inventive concept are the subject of the dependent claims.

The invention includes the idea to contrast the known solutions for reducing the adverse effects in the Leitschichtbereich of thin-film solar cells an intrinsic solution that significantly improves the solar cell regardless of special measures in the module interconnection and assembly in their long-term behavior. It further includes the idea of providing a stabilizing or drift barrier layer at a suitable location and in a suitable embodiment, the provision of which may not be associated with new negative effects on the operating parameters and / or the long-term stability. Finally, the invention includes the idea of providing an amorphous or microcrystalline stabilization layer between the carrier substrate and the respective conductive layer, which unfolds its effect in an electric field.

In one embodiment of the invention, the stabilization layer comprises an alloy of the elements silicon, oxygen, hydrogen and nitrogen. In particular, in this case in the stabilizing layer silicon with a proportion between 20 and 70% by mass, oxygen with a proportion between 1 and 80% by mass, hydrogen with a proportion between 1 and 30% by mass and nitrogen in a proportion between 1 and 60 Mass%, where the sum the proportions is 100 mass%. In appropriate embodiments, the

Stabilization layer as PVD (Physical Vapor Deposition) - or PECVD (Plasma Enhanced Chemical Vapor Deposition) layer executed.

In further embodiments, the stabilization layer has a thickness in the range between 10 nm and 300 nm, more particularly between 40 nm and 120 nm. The stabilization layer is formed in a technologically advantageous manner as a continuous layer, which is produced in a deposition step. In other embodiments, it comprises several sub-layers, which may differ with regard to the presence and content of certain elements (especially those mentioned above), in particular to advantageously realize additional functions (such as antireflection, passivation or diffusion barrier layer).

In a preferred embodiment of the invention, the carrier substrate is a sunlight-transparent front glass, and the stabilization layer is arranged between the front glass and an antireflection layer or between an antireflection layer and the active layer. In a modification of this embodiment, it is provided that the stabilization layer itself at the same time acts as an antireflection layer, as a result of which an additional antireflection layer may possibly even be omitted.

In the latter embodiments, in particular, the stabilizing layer is transparent to sunlight, and specifically has a transmission coefficient of 80% or more in the wavelength range between 350 nm and 1200 nm. In another embodiment, the stabilization layer has a refractive index at 600 nm in the range between 1.5 and 2.5, more particularly in the range between 1.6 and 2.0.

Another embodiment is characterized in that the or an additional Liehe stabilization layer between a back glass or a back reflector layer (white color, foil, etc.) and a back-side conductive layer is provided on the active layer. Typically, this backside occurs Placement of a stabilizing layer not on their transparency or other optical properties. However, it may be technologically advantageous to form them at this point of a solar cell having substantially the same properties and steps as a corresponding layer between front glass and front TCO, especially after the third laser structuring step in monolithically integrated cells.

The stabilization layer stabilizes the subsequently applied TCO layer. Presumably, it prevents the drift of harmful substances to the glass TCO interface or into the TCO under the action of an electric field. Eventually, this will prevent the chemical reaction that affects the function of the TCO. This may in particular be related to the increased hydrogen content in the layer. The mentioned resistance increases in the TCO do not occur when using the barrier according to the invention, and the solar module accordingly shows no power losses when positive voltages occur in relation to ground potential. If the layer as additional

Diffusion barrier and / or antireflection layer serves, it has an additional quality-enhancing.

In practice, a version with a silicon active layer is particularly important, but in principle also possible is the design as a solar cell from the CIGS

(Cu (InGa) SeS) - or CdTe-type or as a component of organic photovoltaics etc. Furthermore, in addition to the currently most important version with a ZnO-based conductive layer (TCO) and the implementation with conductive layers on Sn0 ₂ -, TiO or other known base possible.

drawings

Further advantages and advantageous embodiments of the invention

Objects are illustrated by the drawings and explained in the following description. It should be noted that the drawings have only descriptive character and are not intended to limit the invention in any way. Show it: 1 is a schematic cross-sectional view of the layer structure of a thin-film solar cell according to a first embodiment of the invention,

2 is a schematic cross-sectional view of the layer structure of a thin-film solar cell according to a second embodiment of the invention;

Fig. 3 is a schematic cross-sectional view of the layer structure of a thin-film solar cell according to a third embodiment of the invention and

4 is a schematic cross-sectional view of the layer structure of a thin-film solar cell according to a fourth embodiment of the invention.

Fig. 1 shows a first layer structure, wherein - as in the other figures - serving as a carrier substrate transparent front glass 11 is shown as the lowermost layer of the solar cell 10. Here, a stabilization layer 13 is located between the carrier substrate 11 and a front-side conductive layer 15a, to which a silicon layer 17 as an active layer (which may comprise several partial layers) follows in the selected representation. This is provided with a backside conductive layer (backside TCO) 15b, and then followed by a backside glass 19 as the rear end of the structure. (A back reflector or a laminating film provided under the back glass 19 is not shown in the figure.)

The structure shown in Fig. 2 is substantially the same as that shown in Fig. 1, and so far reference numerals to Fig. 1 have been used, and the corresponding layers will not be described again here. The only difference is the additional presence of an antireflection layer 24 between the stabilization layer 23 and the front TCO 25a. In the embodiment according to FIG. 3, only the sequence of stabilization in comparison to FIG. 2 is shown. layer 33 and the antireflective layer 34 reversed; otherwise the structure is the same.

In the embodiment according to FIG. 4, the solar cell 40 essentially has the same structure as the solar cell 10 according to FIG. 1, with the sole exception that a second stabilization layer 48 is provided between the rear TCO 45b and the rear-side glass 49 , which gives comparable effects to the backside TCO as in the other versions at the front TCO. Hereinafter, two embodiments of specific layer compositions will be given with reference to each one specific manufacturing method of the stabilizing layer.

Embodiment 1

Deposition in PECVD reactor with composition corresponding to the following gas flows and plasma power

Embodiment 2

Deposition in PECVD reactor with composition corresponding to the gas flows and plasma power

SiH ₄ C0 ₂ H ₂ (sccm) P (W) Time (s) Thickness Break. (sccm) (sccm) (nm) index

530 3743 4000 200 1300 = 130 1.77 Within the scope of expert action, further refinements and embodiments of the method and apparatus described here by way of example only arise.

Claims

claims Thin-film solar cell (10; 20; 30; 40) with a carrier substrate  (11; 21; 31; 41), in particular glass substrate, and a radiation-absorbing photoelectric active layer (17; 27; 37; 47) arranged on the carrier substrate, in particular of a semiconductor material or an organic material having a photovoltaic effect, and one between the carrier substrate and the active layer arranged conductive layer (15a; 25a; 35a; 45a) for electrically connecting the active layer, wherein between the carrier substrate and the conductive layer, an amorphous and / or microcrystalline stabilization layer (13; 23; 33; 43) for preventing ion drift and / or Diffusion from the conductive layer is provided at the interface with the carrier substrate when applying a DC voltage of about ± 50 V to ground. 2. Thin-film solar cell according to claim 1,  wherein the stabilizing layer (13; 23; 33; 43) comprises an alloy of the elements silicon, oxygen, hydrogen and nitrogen. Thin-film solar cell according to claim 2,  wherein in the stabilizing layer (13; 23; 33; 43) silicon in a proportion of between 20 and 70% by mass, oxygen in a proportion between 1 and 80% by mass, hydrogen in a proportion between 1 and 30% by mass and optionally Nitrogen is contained in a proportion between 1 and 60% by mass, wherein the sum of the shares 100% by mass. Thin-film solar cell according to one of the preceding claims, wherein the stabilization layer (13; 23; 33; 43) is designed as a PVD or PECVD layer. 5. Thin-film solar cell according to one of the preceding claims, wherein the stabilizing layer (13; 23; 33; 43) has a thickness in the range between 10 nm and 300 nm, more particularly between 40 nm and 120 nm. A thin film solar cell according to any one of the preceding claims, wherein the stabilizing layer (13; 23; 33; 43) comprises a plurality of sublayers. 7. Thin-film solar cell according to one of the preceding claims,  wherein the support substrate is a sunlight-transparent front glass (21; 31) and the stabilization layer (23; 33) is arranged between the front glass (21) and an antireflection layer (24) or between an antireflective layer (34) and the active layer (37). 8. Thin-film solar cell according to one claims 1 to 6,  wherein the carrier substrate is transparent to sunlight front glass and the stabilizing layer also acts as an antireflection layer. 9. Thin-film solar cell according to claim 7 or 8,  wherein the stabilizing layer (13; 23; 33; 43) is transparent to sunlight and in particular has a transmission coefficient of 80% or more in the wavelength range between 350 nm and 1200 nm. 10. Thin-film solar cell according to claim 7 or 9,  wherein the stabilizing layer (13; 23; 33; 43) has a refractive index at 600 nm in the range between 1.5 and 2.5, more particularly in the range between 1.6 and 2.0. 11. Thin-film solar cell according to one of the preceding claims,  wherein the or an additional stabilization layer (48) is provided between a back glass (49) and a backside conductive layer (45b) on the active layer (47). 12. Thin-film solar cell according to one of the preceding claims,  wherein the active layer (17; 27; 37; 47) comprises a silicon layer.