TW201320378A - Method of manufacturing an intermediate reflective layer - Google Patents

Abstract

An intermediate reflective layer in a thin film tandem solar cell is deposited by a PEDVD in a process environment implanted with a gas mixture comprising H2, SiH4, a dopant gas, and CO2. The ratio of H2 to SiH4 gas flow is selected between 100 and 400 and the highest possible CO2 to SiH4 flux ratio is selected, thus maintaining the conductivity of the layer.

Description

Method of manufacturing an intermediate reflective layer

A photovoltaic device or solar cell is a device that converts light into electrical energy. Thin-film solar cells are particularly important for low-cost mass production because they allow the use of inexpensive substrates (such as glass) and films based on Si with a thickness ranging from 100 nm to 2 microns. One of the most commonly used methods for the deposition of this Si-based layer is the PECVD process.

Simple thin film solar cells typically include a transparent (glass) substrate and a layer of transparent conductive oxide (TCO) deposited on the substrate (ie, the front side contacts (or electrodes) of the solar cell). A germanium substrate layer is deposited on the TCO front contact: first a positively doped Si layer (ie, a p-layer), then an intrinsic absorber layer (i-layer) and a negatively doped n-layer. The three Si layers form a p-i-n junction. The main portion of the thickness of the Si layer is occupied by the i-layer and photoelectric conversion mainly occurs here. On top of the Si layer, another layer of TCO (also known as the back contact) is deposited. The TCO positive and back contact layers can be made of zinc oxide, tin oxide, ITO or other suitable materials. A white reflector is typically applied after the back contact to reflect light that has not been absorbed back into the active layer.

Figure 1 shows a tandem junction tantalum thin film solar cell as is known in the art. The thin film solar cell 50 generally includes a first or front electrode 42, two or more semiconductor film pin junctions 51 and 43 including respective layers 52-54 and 44-46, and a second or back electrode 47 (which are successively Stacked on the substrate 41). Each p-i-n junction 51, 43 or thin film photoelectric conversion unit comprises a p-type layer 52, 44 and an n-type layer 54, 46 (p- Type = positive doping, n-type = negative doping) intermediate i-type layers 53, 45. In essence, "essence" is understood in this context to be undoped or substantially free of doping. Photoelectric conversion occurs mainly in this i-type layer and, therefore, is also referred to as an absorption layer.

The pin junction of the solar cell or photoelectric (conversion) device has an amorphous phase (a-Si, 53) or microcrystalline (μc-Si, 45) solar energy depending on the crystal component (crystallinity) of the i-type layers 53, 45. The feature of the pin junction is independent of the crystalline nature of the adjacent p and n layers. As is common in the art, a microcrystalline layer is understood to be a layer of germanium crystals (so-called microcrystals) that contain a very large fraction of the amorphous phase matrix. The p-i-n junction stack is called a series or triple junction photovoltaic cell. The combination of an amorphous phase and a microcrystalline p-i-n-junction (as shown in Figure 1) is also referred to as a micromorph series cell.

The present invention relates to a photovoltaic device comprising stacked multi-junctions of the above kind. It is not limited to a series junction cell containing two stacked p-i-n junctions, but many types of multi-junction solar cells can be usefully used, all of which are presented and claimed as "series solar cells" in this description.

It is known in the art that the efficiency of the stacked p-i-n junction types proposed herein can be improved by arranging one or more selectively reflective layers substantially between the junctions. Referring to Figure 1 above, this can be done at the interface of layers 53/54 and/or 54/44 and/or 44/45 and/or even at 45/46. This intermediate layer is also known as the intermediate reflector, abbreviated IRL.

No. 5,021,100 describes a multi-cell photovoltaic device comprising a first and a second series of connected solar pin junctions and a conductive or dielectric selective reflective film therebetween. Selecting the thickness of the selective reflection film to reflect short-wavelength light that can be absorbed by the first solar pin junction (upper surface 51), and transmitting less or less by the upper pin junction but preferably by lower pin Long-wavelength light absorbed by the surface. The selective reflection film may include ZnO, TiO, SnO ₂ , ITO (all of which is electrically conductive), SiO ₂ , SiN, TaO, and SiC (all of which have dielectric properties).

In the present invention, various existing IRLs and improvements in their methods of manufacture have been described which may be used in combination or on their own to further boost efficiency to improve the optical and/or electrical properties of the proposed type of thin film solar cell.

This is achieved by a method of fabricating an intermediate reflective layer IRL in a thin film tandem solar cell comprising a deposition process environment in which a gas mixture comprising H ₂ , SiH ₄ , a dopant gas, and CO ₂ is implanted by PEDVD. A layer is deposited in which the ratio of the H ₂ to SiH ₄ gas flow is between 100 and 400 and the highest possible ratio of CO ₂ to SiH ₄ gas flow is selected, thus maintaining the conductivity of the layer.

Furthermore, the proposed object is achieved by a tandem solar cell comprising at least one layer of IRL, wherein the IRL layer consists essentially of a region rich in SiO and relatively pure SiO, which forms a plurality of substantially A nanostructure of a cord extending in a direction perpendicular to the surface on which the layer is present. Therefore, the structure of the IRL layer material can be studied by electron energy loss spectroscopy and energy filtration transmission electron microscopy (EFTEM), as known, for example, from G. Nicotra, Appl. Surf. Sci 205 ( 2003) or S. Schamm, Ultramicroscopy 108 (2008).

Now, the present invention will be exemplified with the aid of graphics and its specific examples.

As can be understood from the method according to the invention and from the tandem cell according to the invention, one of the materials of the IRL consists essentially of yttrium oxide. Therefore, in the following we will propose an IIR according to the present invention as SOIR (Thyme Oxide Mutual Reflector).

SOIR must achieve low refractive index on the one hand and high lateral electrical conduction on the other hand. However, when the O content in the material is high, the refractive index of the SOIR material is low; when the O content in the material is low, high lateral conduction is achieved.

The effect of hydrogen dilution on the refractive index of light having a wavelength of 600 nm is shown in Fig. 2. It additionally shows three characteristics of the refractive index dependence from the H ₂ /SiH ₄ flux ratio as the CO ₂ /SiH ₄ flux ratio parameter increases in the direction of the arrow. Furthermore, in this figure there is shown a delimitation of the SOIR layer material from conductive to blocking the cell.

As the H ₂ /SiH ₄ flux ratio increases, it can be seen that when the SOIR layer material becomes resistive, the delimiting feature is shifted toward a lower index of refraction. Therefore, in the embodiment according to Fig. 2, it can be seen that on the one hand, when the H ₂ /SiH ₄ flux ratio is at 250 and above it, a low refractive index of slightly more than 1.8 is reached; and when a relatively high selection is made The COIR layer material is still electrically conductive when the CO ₂ /SiH ₄ flux ratio.

The embodiment according to Fig. 2 is produced from a SOIR layer material deposited using PECVD (especially VHF PECVD), implanting SiH ₄ , H ₂ , CO ₂ into a deposition process environment and using PH ₃ as a dopant gas. Therefore, it can be said that the SOIR layer is deposited in a process environment by PECVD, which injects a gas mixture containing H ₂ , SiH ₄ , a dopant gas, and CO ₂ , wherein the ratio of H ₂ to SiH ₄ is 100. Up to 400, so the conductivity of the resulting layer is maintained by selecting the highest possible CO ₂ to SiH ₄ flux ratio. As seen in Figure ₂ , a similar refractive index is achieved at different H ₂ /SiH ₄ flux ratios, but whether the SOIR material remains conductive is ultimately controlled by the CO ₂ /SiH ₄ flux ratio. It is therefore advantageous to use two separate variables (on the one hand the H ₂ /SiH ₄ flux ratio, on the other hand the CO ₂ /SiH ₄ flux ratio) to achieve two requirements (in other words, on the one hand low) A refractive index, on the other hand, a high lateral electrical conduction) SOIR material.

It is known that the nanostructure of the resulting SOIR layer material is clearly decisive.

The nanostructures of the three SOIR layer materials achieved when diluted with different H ₂ /SiH ₄ are shown in Figure 3. Left by the "blocking" of labeled material exhibits substantially unstructured SiO _x material. This is at a low dilution of H ₂ /SiH ₄ of 3.

At the dilution of 100, according to the central representation by the "boundary" mark, a black region rich in SiO _x and a relatively pure region (white region) of SiO which can be distinguished from each other can be identified. Initially, the long cable structure can be identified in a direction substantially perpendicular to the surface on which the layer is present. The average length of the SiO richer cord region in the deposition growth direction is at least in the range of 5 nm to 10 nm. This SOIR layer material already has electrical conductivity.

The material labeled "conductive" on the right hand side is established at the 300 dilution according to Figure 2. In which the average length in the growth direction of the SiO rich cord region is greater than 20 nm, however it is in a direction perpendicular thereto The average length is less than 10 nm.

This material has good electrical conductivity and combines a low refractive index.

The layer material resulting from the "conducting" layer material of Figure 3 was further deposited on the rough ZnO surface forming the triangular pyramid (as shown in Figure 4). The μc-Si layer is interposed between the ZnO and SOIR materials. It has been clearly established that the nanostructure of the SOIR material is deposited on a rough surface with an average peak to peak roughness of at least 200 nm.

This substantially expands the range of possible applications for this SOIR layer.

For the manufacture of the intermediate reflective layer IRL (and therefore the SOIR according to the invention), a further process parameter that must be carefully considered is the deposition rate, especially in view of industrial manufacturing.

Figure 3 shows that at a H ₂ /SiH ₄ flux ratio of 100, on the one hand (see Figure 2), the refractive index is at the upper limit and the conductivity is at the lower limit. However, at a H ₂ /SiH ₄ flux ratio of 300, both the refractive index and the conductivity are improved, and Fig. 5 shows that the growth rate decreases as the flux ratio of H ₂ /SiH ₄ increases. Thus, in a preferred embodiment of the method according to the invention, a ratio of H ₂ to SiH ₄ flux of at least about 300 is selected (according to Figure 5), which still produces an acceptable deposition rate of about 0.6 angstroms per second. .

By appropriately modifying the deposition method, the CO ₂ to SiH ₄ flux ratio and the amount of doping gas are properly adjusted so that the deposition rate is further increased to about 3.5 at a refractive index of 1.66 for light of a wavelength of 600 nm. Angstroms per second, and it is possible to maintain a substantially fine sonan structure that is substantially in accordance with the SOIR material shown on the right hand side of Figure 3. Therefore, it has been found that achieving further optimization as proposed herein involves considering the overall oxygen content in the layer material.

As shown in Figure 6, it shows that as the overall oxygen content in the layer material is increased, the refractive index decreases toward a high desired low value. Figure 6 shows a further preferred embodiment of the process according to the invention which is present to maximize the overall oxygen content in the layer material, preferably from 39% to 52%, preferably at least 50%. At this oxygen content, the refractive index of light at a wavelength of 600 nm becomes significantly lower as desired.

Figure 7 shows a good example of providing an IRL (SOIR according to the invention). According to Fig. 7, the tandem solar cell comprises a-Si and μc-Si p-i-n junctions 51a and 43a. As shown, in a specific embodiment according to Fig. 7, at least one of the two electrode layers of the front and back electrode layers 47a and 42a is ZnO. As for the substrate, the substrate 41a is preferably made of glass. The p-i-n junction 51a on a-Si is present on the front surface electrode 42a.

The deposited IRL layer 60 (imagined as an SOIR layer in accordance with the present invention) is expanded as an n-doped layer and a portion of the thickness of the n-doped layer 54a of the upper a-Si p-i-n junction 51a. Thus, as shown in the good example of Figure 7, the proposed IRL layer 60 is buried within the n-layer 54a.

As seen from Fig. 7, in a good specific example of manufacturing a tandem cell according to the present invention, the latter comprises a-Si and μc-Si p-i-n junctions 51a and 43a. Therefore, in a good specific example, at least one of the positive and back electrode layers is deposited with ZnO. Therefore, in a good specific example, the front electrode is present on the glass substrate 41a, followed by the a-Si p-i-n upper surface 51a. The IRL layer 60 is deposited as an n-doped layer and spread over a portion of the thickness of the n-layer 54a of the a-Si p-i-n junction. In a preferred embodiment, the IRL layer 60 is embedded in the n-layer of the a-Si p-i-n junction.

As seen from Fig. 7, the goodness of the series battery according to the present invention Examples include an a-Si and μc-Si p-i-n junction, a positive and a back electrode layer. Therefore, in a good specific example, at least one of the positive and back electrode layers is substantially ZnO. In a good embodiment, the front electrode is present on a glass substrate. In a preferred embodiment, the a-Si p-i-n upper junction is present on the front electrode layer. In a preferred embodiment, the IRL layer is an n-doped layer that extends over a portion of the thickness of the n-layer of the a-Si pin junction, and in further preferred embodiments, it is embedded in a-Si In the n layer of the pin junction.

The IRL (more specifically, the SOIR layer 60) is provided in a tandem solar cell in a structure as shown in Figure 7. The proposed layer was deposited at a deposition rate of 3.5 angstroms per second. When the nanostructure of the SOIR material is maintained, a low refractive index of at least about 1.7 is achieved. The thickness of the SOIR layer 60 is 60 nm.

Figure 8 shows the features produced by the tandem solar cell whereby the features proposed by (a) are compared in series according to Figure 7 but without the features of the IRL layer 60. This feature (b) is derived from the features of the series connected cell with the IRL layer 60 proposed. Regarding the thickness of the SOIR layer, experiments have shown that in a good specific example, the thickness is 40 to 90 nm, and thus in a modified specific example, 60 to 80 nm. It is obvious that the target is a minimum thickness, for example, from the viewpoint of industrial manufacturing. Thus, a good specific example of the method according to the invention results in the self-deposition of an IRL (SOIR) layer having a thickness of 40 nm to 90 nm, further improving the system from 60 nm to 80 nm.

The improvement on the tandem cell without the IRL as shown in Fig. 7 is known to the skilled person: Voc, form factor FF and battery current Isc are all improved.

The initial efficiency was 12.8%, and its solar exposure over 1000 hours was stable to 11.2%. Therefore, good stability is also achieved for high deposition rates.

Fig. 9 is a view showing a series battery having no IRL layer according to Fig. 7 and a series battery including an IRL layer 60 according to the present invention according to Fig. 7, and a battery characteristic according to Fig. 8. In Fig. 9, the feature (a1) proposes an initial feature of a series cell without IRL, and (a2) proposes a feature of the series cell without IRL after 1000 hours of solar exposure; this feature (b1) is proposed according to the invention Thus the initial feature of the series cell containing IRL, and feature (b2), characterizes the tandem cell containing the IRL according to the invention after 1000 hours of daylight exposure.

Some of the key points of the research so far:

‧ The nanostructure of the IRL material as proposed above is decisive for the good electrical properties of the resulting tandem cell.

‧ High cell current is achieved at low refractive index, in other words 14.3 mA/cm 2 , and the IRL layer is deposited on rough as grown LPCVD ZnO.

‧ The nanostructure and the refractive index down to or even below 1.7 are achieved even at high deposition rates of up to 3.5 angstroms per second.

‧ The resulting tandem cell showed no Voc light decay and 11.2% stable efficiency.

It has been shown that a good SOIR (cerium oxide inter-reflector) according to the present invention should comprise a SiO _x having a refractive index between 1.7 and 1.9 and a thickness between 40 and 90 nm (preferably 60 to 80 nm). Floor. With an oxygen content of 39-52%, this even lower refractive index value can be achieved, as already shown.

In a preferred embodiment, the IRL layer is arranged as part of the n-layer 54 (buried therein), which is correspondingly doped to increase conductivity.

In further preferred embodiments, the IRM layer can be deposited in a process environment comprising Ar. SiH ₄ , CO ₂ and dopant gases were added as indicated to achieve crystallinity and conductivity.

The addition of argon to the deposition gas for this IRL deposition allows the refractive index n of the IRL to shift towards a lower value, as shown in FIG.

As can be seen from Figure 10, the addition of Ar to the process environment reduces the refractive index, which becomes more pronounced as the processing pressure increases. The refractive index can be reached below 1.7, for example with a processing pressure of 4 mbar.

Process conditions / flux (sccm) is:

H ₂ : 1500

SiH ₄ : 15

PH ₃ (0.1%): 500

CO ₂ :25

CO ₂ /SiH ₄ = 1.67 (flux ratio)

Power: ~850 watts

The addition of 100 sccm Ar to the above formulation resulted in a considerable transfer of the refractive index to 1.7 and even below.

IRL layer of the conductive material may be used by the respective n-doped implanted dopant (especially PH ₃₎ and pushed up. Thus, Figure 11 shows the ratio of the refractive index development of the IRL layer material to the flux ratio of CO ₂ /SiH ₄ and the dependence of the addition of Ar to the processing environment. There are plenty of reasons in Figure 11:

Left hand indicating triangle: 50 sccm PH ₃ (2%) equals 1.0 sccm PH ₃

Right hand indicating triangle: 100 sccm PH ₃ (2%) equals 2.0 sccm PH ₃

Fill the mark = block the battery.

Process conditions / flux (sccm):

H ₂ : 1500 (up to 1950)

SiH ₄ : 15

(PH ₃ (0.1%): 500)

Power: ~850 watts

Pressure: 4 mbar

Figure 12 shows the effect of the deposition rate on the refractive index of the IRL layer material. It is noted that the minimum refractive index is reached over a range of deposition rates from 3.3 angstroms per second to 3.8 angstroms per second down to about 1.7.

In the following examples, the effect of Ar and PH ₃ (2%) on a non-microcrystalline tandem cell at a CO ₂ flux of 32 sccm was investigated.

1) The battery parameters are:

4.5 micron ZnO

250 nm a-Si: H battery

60 nm yttria mutual reflector (SOIR)

1.8 micron μc-Si:H

The process parameters are:

Figures 13 and 14 show the results. For the result (a), the refractive index of the material of the IRL layer was 1.66 at a deposition rate of 3.4 angstroms/second.

2) The battery parameters are:

AR glass

2 micron thick ZnO

280 nm a-Si:H

60 nm thick SOIR or 80 nm thick SOIR (named System B)

2.4 micron μc-Si:H

The process parameters for SOIR are:

The results are shown in Figures 15, 16, 17 and 18.

The initial characteristics of the resulting non-microcrystalline tandem cell are shown in Figure 19, and the features after light decay are in Figure 20:

Feature (a): no SIOR coating, SOIR thickness 60 nm

Characteristic (b): having the process parameter 50 sccm PH ₃ 2% as proposed above, SOIR thickness 60 nm

Characteristic (c): having 100 sccm PH ₃ 2% and 100 sccm Ar flux as proposed above, SOIR thickness 60 nm

Characteristic (d): SOIR thickness is 80 nm.

The addition of Ar to the H ₂ , SiH ₄ , CO ₂ , PH ₃ mixture as established, or the partial replacement of H ₂ by Ar thus results in a fixed H ₂ +Ar gas flow, thereby further studying whether it is on the IRL dependency Differences.

A) Add airflow:

Flux (sccm):

H ₂ : 1900

SiH ₄ : 15

PH ₃ (2%): 100

CO ₂ : 32

CO ₂ /SiH ₄ : 2.13

Ar: 0 to 290

Power: about 850 watts

B) Fixed airflow:

Flux (sccm):

H ₂ +Ar:1900

SiH ₄ : 15

PH ₃ (2%): 100

CO ₂ : 32

CO ₂ /SiH ₄ : 2.13

Ar: 0 to 290

Power: about 850 watts

The results are shown in Figure 21.

Please note that the value of n reaches 1.56. Therefore, increasing the amount of Ar in the deposition processing environment for the SOIR layer will reduce the deposition rate.

Figure 22 shows this reduction in fixed airflow processing according to B).

For the proposed SOIR deposition process B), Figure 23 shows the oxygen content in the layer material and the refractive index of the layer material and the Ar gas flow. Dependency. In Fig. 23, the measurement point (a) proposes an oxygen content, and the mark (b) is a point of the refractive index.

Note that it is consistent with Figure 6: measurements on the nanostructure show an O concentration of 52%, n = 1.71; an O concentration of 48%, n = 1.82; an O concentration of 39%, n = 1.88.

Since Ar replaces H ₂ under fixed gas flow processing, the flux ratio of H ₂ /SiH ₄ decreases, and since Figure 5 shows an increase in deposition rate at a reduced H ₂ /SiH ₄ flux ratio, the fixed gas flow is processed. The deposition rate should be increased as the Ar flux increases.

The deposition rate of the IRL material and the dependence of the refractive index on the SiH ₄ flux were investigated along with the following processing parameters. The results are shown in Figure 24. Point (a) proposes a measurement point of the deposition rate, and point (b) is a refractive index.

Note that increasing the SiH ₄ flux at a fixed H ₂ flux results in a decrease in the H ₂ /SiH ₄ flux ratio. Therefore, consistent with the previous results (see Figure 2), the IRL material becomes too resistive at a sufficiently high SiH ₄ flux (see full measurement point). It is to be understood that the refractive index is still substantially stable and is unaffected by the varying SiH ₄ flux.

Process parameters:

Flux (sccm):

H ₂ : 1500

PH ₃ (2%): 50

CO ₂ : 32-64

CO ₂ /SiH ₄ :2.1

Power: 850 watts

We have found further focus as our research:

For non-microcrystalline tandem cells, high rate SOIR (~3.5 angstroms per second) works well: no current loss, similar optical benefits at low rate SOIR, no or very little extra degradation.

A deposition rate of about 4 angstroms per second (for a thin SOIR of 50-60 nm) should probably have good performance.

This formulation can be used at the back of a non-microcrystalline cell for n-SiOx. A thick transparent layer can be added to the battery performance.

41,41a‧‧‧Substrate

43,43a‧‧‧Battery

45‧‧‧Microcrystalline i-type layer

47,47a‧‧‧Back electrode

50‧‧‧Thin solar cells

53‧‧‧Amorphous phase i-type layer

42,42a‧‧‧ front electrode

44,52‧‧‧p-type layer

46, 54, 54a‧‧ n-type layer

48‧‧‧Back reflector

51, 51a‧‧‧Battery

60‧‧‧IRL layer

Figure 1 is a diagram showing a prior art tandem film tantalum photovoltaic cell.

Figure 2 shows the dependence of the refractive index on the H ₂ /SiH ₄ flux ratio as applied in the VHF PECVD deposition method of the intermediate reflective layer according to the present invention.

Figure 3 shows the three nanostructures of the IRL material deposited at the respective H ₂ /SiH ₄ flux ratios, which are the results of electron energy loss spectroscopy/energy filtration through electron microscopy.

Figure 4 shows the nanostructure of an IRL material according to the present invention deposited on a rough ZnO surface profile.

Figure 5 shows the dependence of the deposition rate of the deposited IRL material layer on the H ₂ /SiH ₄ flux ratio.

Figure 6 shows the dependence of the refractive index of the IRL layer material on the oxygen content in the material.

Figure 7 is a diagram showing the specificity of the series battery according to the present invention. Example.

Fig. 8 shows the characteristics of the series battery according to the specific example of Fig. 7.

Figure 9 shows the decay characteristics of a series cell comprising an IRL layer according to Figure 7 and having an IRL layer in accordance with the present invention.

Figure 10 shows the dependence of the refractive index on the deposition process pressure at different amounts of Ar in the processing environment.

Figure 11 shows the dependence of the refractive index of the LRL layer material on the ratio of CO ₂ /SiH ₄ flux as applied to the deposition processing environment.

Figure 12 shows the dependence of the refractive index of the IRL material on the deposition rate of the deposited material.

Figure 13 shows the dependence of the battery current Isc on the different amounts of dopant gas and Ar used in the deposition processing environment.

Figure 14 shows the dependence of the different processing according to Figure 13 on the resulting battery efficiency.

Figure 15 again shows the dependence of the different processing of Figures 13 and 14 on the initial and decaying battery voltage Voc.

Figure 16 again shows the dependence of the proposed different processing on the initial and declining membrane factors.

Figure 17 again shows the dependence of the proposed processing on the initial and decaying battery current Isc.

Figure 18 again shows the dependence of the proposed processing on the initial and reduced efficiency.

Figures 19 and 20 show the initial and decay characteristics of a series cell fabricated with an IRL layer processed in a different manner than the proposed Figures 13-18.

Figure 21 shows the dependence of the refractive index of the IRL layer material on the amount of Ar present in the layer deposition process environment.

Figure 22 shows the dependence of the deposition rate on the amount of argon that flows into the IRL layer deposition process environment.

Figure 23 shows the dependence of the oxygen content in the IRL layer material and the respective refractive indices on Ar in the process environment.

Figure 24 shows the deposition rate and the dependence of the refractive index on the SiH ₄ gas flow.

Claims (18)

A method of fabricating an intermediate reflective layer (IRL) in a thin film tandem solar cell, comprising depositing a layer in a process environment for injecting a gas mixture comprising H ₂ , SiH ₄ , a dopant gas, and CO ₂ by PEDVD, wherein The ratio of H ₂ to SiH ₄ gas flow is between 100 and 400, and the conductivity of the layer is maintained by selecting the highest possible CO ₂ to SiH ₄ flux ratio. For example, in the method of claim 1, the PH _{3 is} injected as a doping gas into the process environment. The method of claim 1 or 2, comprising selecting the H ₂ to SiH ₄ flux ratio to be at least about 300. A method as claimed in any one of claims 1 to 3, which maximizes the overall oxygen content in the layer, preferably from 39% to 52%, preferably at least 50%. The method of any one of claims 1 to 4, wherein the tandem solar cell comprises a-Si and a μc-Si pin junction, preferably at least one of a positive and a back electrode layer, wherein ZnO is preferred. The front electrode is present on the glass substrate, and then the a-Si pin upper surface, the IRL layer is deposited as an n-doped layer on the thickness of the n-layer of the a-Si pin junction The extension, preferably embedded in the n-layer of the a-Si pin junction. The method of claim 5, comprising depositing the IRL layer having a thickness of from 40 nm to 90 nm, preferably from 60 nm to 80 nm. A method of applying one of claims 1 to 6 includes adding Ar to the process environment. The method of claim 7, comprising minimizing the refractive index of the material of the IRL layer by the processing pressure. Patent application methods such as a range of 1 to 8, comprising generating by adjusting PH ₃ n- dopant flux to push up a conductive material layer of the IRL. A tandem solar cell comprising at least one layer of an IRL, the IRL layer consisting essentially of a Si-substrate region that is substantially rich in SiO and relatively pure in SiO, forming a nanowire with a line substantially perpendicular to the surface present on the layer structure. The tandem solar cell of claim 10, wherein the cord of the SiO rich region has an average length in the direction of at least in the range of 5 nm to 10 nm. The tandem solar cell of claim 2, wherein the average length is greater than 20 nm. A tandem cell according to any one of claims 10 to 12, wherein the IRL layer is deposited on a rough surface having an average peak to peak roughness of at least 200 nm. The tandem cell of the invention of claim 10, wherein the material of the IRL layer has an oxygen content of 39% to 52%, preferably at least 50%. A tandem cell according to any one of claims 10 to 14, which comprises an a-Si and a μc-Si pin junction, a positive and a back electrode layer, wherein at least one of the electrode layers is preferably substantially ZnO Preferably, the front electrode is present on the glass substrate, and the a-Si pin junction is present on the front electrode layer, the IRL layer is an n-doped layer and the a-Si pin junction is n Extending a portion of the thickness of the layer, preferably Buried in the n-layer of the a-Si p-i-n junction. A tandem cell according to any one of claims 10 to 15, wherein the IRL layer has a thickness of 40 to 90 nm, preferably 60 to 80 nm. A tandem cell according to any one of claims 10 to 16, wherein the material of the IRL layer has a refractive index of not more than 1.7 to 1.9 for light having a wavelength of 600 nm. A tandem cell according to any one of claims 17 wherein the material of the IRL layer has a refractive index of less than 1.7 for light having a wavelength of 600 nm.