TW201817016A - Solar cell - Google Patents

Abstract

A solar cell includes a substrate, an emitter layer, a back surface field layer, an anti-reflective layer, an alumina layer, a passivation layer, a front electrode and a back electrode. The emitter layer is located within the substrate and adjacent to a front surface of the substrate. The surface field layer is located within the substrate and adjacent to a back surface of the substrate. The anti-reflective layer is located on the front surface of the substrate. The Aluminum oxide layer is located on the back surface of the substrate. The passivation layer includes a first silicon nitride layer, a second silicon nitride layer and a third layer of silicon nitride which are arranged in sequence. The ratio of the hydrogen content to the nitrogen content of the first silicon nitride layer is less than the ratio of the hydrogen content to the nitrogen content of the second silicon nitride layer. The first silicon nitride layer contacts the aluminum oxide layer, and the nitrogen contents of the first and third silicon nitride layers are more than the nitrogen content of the second silicon nitride layer, respectively.

Description

 Solar battery  

The present invention relates to a solar cell, and more particularly to a solar cell having a passivation layer having a hydrogen ion concentration gradient design.

A solar cell is an energy-converting photovoltaic device in which an emitter passivation and a back electrode solar cell (PERC: Passivated Emitter Rear Cell) are attracting attention with their high conversion efficiency. The main difference between emitter passivation and back electrode solar cells compared to conventional solar cells is that the emitter passivation and back electrode solar cells use passivation techniques to passivate the front emitter and back side to reduce surface defects.

In detail, the method of forming the back electrode of the emitter passivation and the back electrode of the solar cell is generally to first open the hole in the passivation layer by laser or the like to form an electrode contact position, and then screen the non-penetrating aluminum glue on the back side. Or it is plated with aluminum by physical vapor deposition (PVD), and finally formed by co-sintering with the front screen printing silver paste to form an electrode, which is printed and sintered on the back side with a conventional aluminum solar cell to form a comprehensive back surface electric field ( BSF: back-surface field) is different. Since the emitter passivation and the back electrode solar cell are fabricated only by partial opening on the back side, a local back field (Local BSF) can be formed and a large area of the passivation layer can be retained. On the other hand, compared with conventional batteries, the emitter passivation and back electrode solar cells increase the passivation layer passivation area on the back side, thereby effectively reducing the rate at which the carriers recombine on the back side.

Referring to FIG. 1, a solar cell 9 of a conventional emitter passivation and back electrode includes a conductive substrate 91, an emitter layer 92, an anti-reflection layer 93, a passivation layer 94, a front surface electrode 95, and a back surface. Electrode 96. The passivation layer 94 refers to a single layer of tantalum nitride layer. However, the thickness of the single-layer tantalum nitride layer is, for example, about 250 nm, and a too thick tantalum nitride layer will result in a long process time. If the single-layer tantalum nitride layer is directly thinned and the passivation of the germanium substrate surface is performed by only one layer, the thinned single layer of tantalum nitride layer may not provide sufficient hydrogen ions to fill the germanium substrate. Surface defects (hanging bonds), in turn, do not adequately achieve surface passivation.

Therefore, there is a need to provide a solar cell that can solve the aforementioned problems.

It is an object of the present invention to provide a solar cell having a passivation layer having a design of a hydrogen ion concentration gradient.

According to the above objective, the present invention provides a solar cell including a substrate, an emitter layer, a back field layer, an anti-reflection layer, an aluminum oxide layer, a passivation layer, a front electrode, and a back electrode. The substrate is of a first conductivity type and has a front side and a back side opposite the front side. The emitter layer is of a second conductivity type and is located within the substrate adjacent the front side. The back electric field layer is of a first conductivity type and is located in the substrate near the back surface. The anti-reflective layer is located at the front side. The aluminum oxide layer is located at the back surface. The passivation layer includes a first tantalum nitride layer, a second tantalum nitride layer and a third tantalum nitride layer arranged in sequence. The ratio of the hydrogen content/nitrogen content of the first tantalum nitride layer is smaller than the ratio of the hydrogen content/nitrogen content of the second tantalum nitride layer. The first tantalum nitride layer contacts the aluminum oxide layer, and the nitrogen content of the first tantalum nitride layer and the third tantalum nitride layer are respectively greater than the nitrogen content of the second tantalum nitride layer. The front electrode passes through the anti-reflective layer and contacts the emitter layer. The back electrode passes through the passivation layer and the aluminum oxide layer and contacts the back electric field layer.

Compared with the prior art, if the total thickness of the multilayer tantalum nitride layer (that is, the first to third tantalum nitride layers) of the passivation layer of the present invention is reduced to less than 250 nm (for example, the total thickness is reduced to 150 nm), The design of the hydrogen ion concentration gradient of the invention is still effective in providing sufficient hydrogen ions to fill defects (dangling bonds) on the surface of the substrate to effectively achieve surface passivation. Or, compared with the prior art, if the total thickness of the multilayer tantalum nitride layer of the passivation layer of the present invention is maintained at 250 nm (for example, the film thicknesses of the first, second, and third tantalum nitride layers are 10 nm, 10 nm, and 230 nm, respectively). ), since the design of the hydrogen ion concentration gradient of the present invention can more fully achieve substrate surface passivation, the performance of the solar cell of the present invention (for example, series resistance Rs, short circuit current Isc, open circuit voltage Voc, and fill factor FF) can be Improve again.

1‧‧‧Solar battery

11‧‧‧Substrate

111‧‧‧ positive

112‧‧‧Back

112H‧‧‧ Openings

112M‧‧‧around the opening

12‧‧ ‧ emitter layer

13‧‧‧Anti-reflective layer

14‧‧‧ Passivation layer

14'‧‧‧ Passivation layer

141‧‧‧First tantalum layer

142‧‧‧Second tantalum layer

1421‧‧‧First tantalum nitride film

1422‧‧‧Second tantalum nitride film

143‧‧‧the third layer of tantalum nitride

1431‧‧‧ outside

144‧‧‧buffer layer

1441‧‧‧The third tantalum nitride film

1442‧‧‧4th tantalum nitride film

1443‧‧‧Film nitride film

145‧‧‧4th tantalum nitride layer

146‧‧‧矽Nitrogen oxide layer

147‧‧‧矽Oxide layer

15‧‧‧Front electrode

16‧‧‧Back electrode

17‧‧‧ Back electric field layer

18‧‧‧Alumina layer

9‧‧‧Solar battery

91‧‧‧Substrate

92‧‧ ‧ emitter layer

93‧‧‧Anti-reflective layer

94‧‧‧ Passivation layer

95‧‧‧ front electrode

96‧‧‧Back electrode

1 is a schematic cross-sectional view of a conventional emitter passivation and back electrode solar cell.

2 is a schematic cross-sectional view of a solar cell according to an embodiment of the present invention.

3 is a partial cross-sectional view showing a solar cell according to an embodiment of the present invention.

4 is a partial cross-sectional view showing a solar cell according to another embodiment of the present invention.

The above described objects, features, and characteristics of the present invention will become more apparent from the aspects of the invention.

Referring to Figure 2, there is shown a solar cell of one embodiment of the present invention. The solar cell 1 includes a substrate 11, an emitter layer 12, a back electric field layer 17, an anti-reflection layer 13, an aluminum oxide layer 18, a passivation layer 14, a front electrode 15, and a back electrode 16. The substrate 11 is of a first conductivity type (for example, a germanium substrate) and has a front surface 111 and a back surface 112 opposite to the front surface 111. The emitter layer 12 is of a second conductivity type and is located within the substrate 12 near the front side 111. The back electric field layer 17 is of a first conductivity type and is located in the substrate 11 near the back surface 112. The anti-reflection layer 13 is located at the front surface 111. The aluminum oxide layer 18 is located at the back side 112. The front electrode 15 passes through the anti-reflection layer 13 and contacts the emitter layer 12. The back electrode 16 passes through the passivation layer 14 and the aluminum oxide layer 18 and contacts the back electric field layer 17.

In this embodiment, the solar cell 1 of the present invention may be a passive passivated and back electrode solar cell (PERC: Passive Emitter Rear Cell), which is heavily doped (for example, P+ doping) only at the corresponding opening 112H. That is, the doping concentration is slightly higher than that of the substrate 11 (for example, a P-type conductivity type), and such an opening portion 112H is referred to as a local back-surface field (LBSF). In another embodiment, the solar cell 1 of the present invention may be an emitter-passivated and fully diffused solar cell (PERT: Rear-Rand Totally-Diffused), and the opening 112H is heavily doped (for example, P++doping) There is a doping (for example, P+doping) at the periphery of the opening 112M, that is, both P++ doping and P+ doping having a higher doping concentration than the substrate 11 (for example, a P-type conductivity type).

Referring to FIG. 3, in the embodiment, the passivation layer 14 includes a first tantalum nitride layer 141, a second tantalum nitride layer 142, and a third tantalum nitride layer 143. The first tantalum nitride layer 141 contacts the aluminum oxide layer 18. The refractive index of the first tantalum nitride layer 141 is smaller than the refractive index of the second tantalum nitride layer 142, and the refractive index of the third tantalum nitride layer 143 is also smaller than the refractive index of the second tantalum nitride layer 142. For example, the refractive indices of the first and third tantalum nitride layers 141 and 143 are both less than 2, and the refractive index of the second tantalum nitride layer 142 is greater than 2.4, so that the first tantalum nitride layer 141 and The nitrogen content of the third tantalum nitride layer 142 is greater than the nitrogen content of the second tantalum nitride layer 142, that is, the hydrogen content of the first tantalum nitride layer 141 and the third tantalum nitride layer 143 are also less than The hydrogen content of the second tantalum nitride layer 142. Therefore, the ratio of the hydrogen content/nitrogen content of the first tantalum nitride layer 141 is smaller than the ratio of the hydrogen content/nitrogen content of the second tantalum nitride layer 142, and a concentration gradient of hydrogen ions can be formed. The hydrogen ion concentration gradient is designed such that the hydrogen ions are effectively moved from the second concentration of the second tantalum nitride layer 142 to the lower concentration of the first tantalum nitride layer 141, and the substrate 11 is added (for example, germanium). Defects (dangling bonds) on the surface of the substrate also attract hydrogen ions to move in the direction of the substrate 11. In addition, the ratio of the hydrogen content/nitrogen content of the third tantalum nitride layer 143 is smaller than the ratio of the hydrogen content/nitrogen content of the second tantalum nitride layer 142, and the third tantalum nitride layer 143 is used as the hydrogen ion barrier layer. .

Compared with the prior art, if the multilayer tantalum nitride layer of the passivation layer 14 of the present invention (that is, the first to third tantalum nitride layers 141, 142, 143) has a total thickness of less than 250 nm (for example, total thickness drop) Up to 150 nm), the design of the hydrogen ion concentration gradient of the present invention is still effective in providing sufficient hydrogen ions to fill defects (dangling bonds) on the surface of the substrate to effectively achieve surface passivation. Alternatively, compared to the prior art, if the total thickness of the multilayer tantalum nitride layer of the passivation layer 14 of the present invention is maintained at 250 nm (for example, the film thicknesses of the first, second, and third tantalum nitride layers 141, 142, and 143, respectively) 10 nm, 10 nm, and 230 nm), since the design of the hydrogen ion concentration gradient of the present invention can more fully achieve substrate surface passivation, the performance of the solar cell of the present invention (for example, series resistance Rs, short-circuit current Isc, open circuit voltage Voc) And the fill factor FF) can be further improved.

Referring to FIG. 4, in another embodiment, the second tantalum nitride layer 142 of the passivation layer 14' includes first and second tantalum nitride films 1421, 1422. The passivation layer 14' further includes a buffer layer 144 including third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443. The first tantalum nitride layer 141, the third tantalum nitride film 1441, the first tantalum nitride film 1421, the fourth tantalum nitride film 1442, the second tantalum nitride film 1422, and the fifth nitride The tantalum film 1443 and the third tantalum nitride layer 143 are sequentially arranged.

The refractive indices of the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443 are smaller than the refractive indices of the first and second tantalum nitride films 1421, 1422. The refractive indices of the first and third tantalum nitride layers 141, 143 are smaller than the refractive indices of the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443. For example, the first and third tantalum nitride layers 141, 143 have refractive indices of less than 1.9, and the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443 have refractive indices of between 1.9 and 2.4. The refractive index of the first and second tantalum nitride films 1421, 1422 is greater than 2.4, so that the nitrogen content of the first tantalum nitride layer 141 and the third tantalum nitride layer 142 is greater than the buffer. Layer 144 (including third, fourth, and fifth tantalum nitride films 1441, 1442, 1443), the buffer layer 144 (including the third, fourth, and fifth tantalum nitride films 1441, 1442, 1443) nitrogen content The nitrogen content of the second tantalum nitride layer 142 (including the first and second tantalum nitride films 1421, 1422); that is, the hydrogen of the first tantalum nitride layer 141 and the third tantalum nitride layer 143 The content of hydrogen is less than the hydrogen content of the buffer layer 144 (including the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443), and the buffer layer 144 includes third, fourth, and fifth tantalum nitride films 1441. The hydrogen content of 1442, 1443) is less than the hydrogen content of the second tantalum nitride layer 142 (including the first and second tantalum nitride films 1421, 1422). Therefore, the ratio of the hydrogen content/nitrogen content of the first tantalum nitride layer 141 is smaller than the hydrogen content/nitrogen content of the buffer layer 144 (including the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443). The ratio of the hydrogen content/nitrogen content of the buffer layer 144 (including the third and fourth tantalum nitride films 1441, 1442) is smaller than the second tantalum nitride layer 142 (including the first and second tantalum nitride films) The ratio of hydrogen content to nitrogen content of 1421, 1422) can form a concentration gradient of hydrogen ions. The hydrogen ion concentration gradient is designed such that the hydrogen ions are effectively concentrated from the second tantalum nitride layer 142 having a high concentration (including the first and second tantalum nitride films 1421, 1422) to the first concentration of the first nitride. The movement of the ruthenium layer 141 in the direction of the substrate 11 (for example, a ruthenium substrate) also attracts hydrogen ions to move in the direction of the substrate 11. In addition, the ratio of the hydrogen content/nitrogen content of the third tantalum nitride layer 143 is smaller than the hydrogen content/nitrogen content of the second tantalum nitride layer 142 (including the first and second tantalum nitride films 1421, 1422). The ratio is such that the third tantalum nitride layer 143 functions as a hydrogen ion barrier layer. The buffer layer 144 (including the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443) serves as a buffer for movement.

The passivation layer 14 ′ further includes a fourth tantalum nitride layer 145 disposed on an outer side 1431 of the third tantalum nitride layer 143 and having a defect of the fourth tantalum nitride layer 145 . The content is greater than the germanium content of the first, second and third tantalum nitride layers 141, 142, 143. For example, the fourth tantalum nitride layer 145 has a refractive index greater than 2.4. The fourth tantalum nitride layer 145 can serve as a hydrogen ion last barrier layer.

The passivation layer 14' further includes a tantalum oxynitride layer 146 disposed on an outer side 1451 of the fourth tantalum nitride layer 145. The tantalum oxynitride layer 146 can serve as a paste diffusion block layer. The passivation layer 14' further includes a tantalum oxide layer 147 such as a hafnium oxide layer disposed between the aluminum oxide layer 18 and the back surface 112 of the substrate 11. The thickness of the tantalum oxide layer 147 may be 1 to 2 nm, and the thickness of the aluminum oxide layer 18 may be 4 to 8 nm.

Compared with the prior art, if the passivation layer 14' of the present invention has a plurality of tantalum nitride layers and a hafnium oxynitride layer (that is, the first to third tantalum nitride layers 141, 142, 143, the buffer layer 144, The total thickness of the fourth tantalum nitride layer 145 and the tantalum oxynitride layer 146) is reduced to less than 250 nm, and the hydrogen ion concentration gradient of the present invention is designed to effectively provide sufficient hydrogen ions to fill defects on the substrate surface. (Danging) In turn, surface passivation can be effectively achieved. For example, the first tantalum nitride layer 141 has a film thickness of 10 nm, and the first and second tantalum nitride films 1421 and 1422 of the second tantalum nitride layer 142 have a film thickness of 5 nm. The film thickness of the ruthenium layer 143 is 60 nm, and the film thicknesses of the third, fourth, and fifth tantalum nitride films 1441, 1442, and 1443 of the buffer layer 144 are both 15 nm, and the film of the fourth tantalum nitride layer 145 The thickness is 20 nm, and the film thickness of the tantalum oxynitride layer 146 is 5 nm, so that the total thickness of the multilayer tantalum nitride layer and the tantalum nitride layer of the passivation layer 14' can be reduced to 150 nm. Alternatively, if the total thickness of the multilayer tantalum nitride layer and the tantalum oxynitride layer of the passivation layer 14' of the present invention is maintained at 250 nm compared to the prior art, the design of the hydrogen ion concentration gradient of the present invention can be more fully The substrate surface passivation is achieved, so the performance of the solar cell of the present invention (for example, the series resistance Rs, the short-circuit current Isc, the open circuit voltage Voc, and the fill factor FF) can be further increased.

In summary, the present invention is only described as a preferred embodiment or embodiment of the technical means for solving the problem, and is not intended to limit the scope of the invention. That is, the equivalent changes and modifications made in accordance with the scope of the patent application of the present invention or the scope of the invention are covered by the scope of the invention.

Claims (16)

 A solar cell comprising: a substrate having a first conductivity type, the substrate having a front surface and a back surface opposite to the front surface; an emitter layer being of a second conductivity type, the emitter layer being located in the substrate adjacent to the a front side; a back electric field layer, a first conductivity type, the back electric field layer is located in the substrate near the back surface; an anti-reflection layer is located at the front surface; an aluminum oxide layer is located at the back surface; a passivation layer The first tantalum nitride layer, the second tantalum nitride layer and the third tantalum nitride layer are arranged in sequence, wherein: the ratio of the hydrogen content/nitrogen content of the first tantalum nitride layer is smaller than the first a ratio of hydrogen content/nitrogen content of the hafnium nitride layer; and the first tantalum nitride layer is in contact with the aluminum oxide layer, and the nitrogen content of the first tantalum nitride layer and the third tantalum nitride layer are respectively greater than a nitrogen content of the second tantalum nitride layer; a front electrode passing through the antireflection layer and contacting the emitter layer; and a back electrode passing through the passivation layer and the aluminum oxide layer and contacting the back electric field layer .    The solar cell of claim 1, wherein the first tantalum nitride layer has a hydrogen content smaller than a hydrogen content of the second tantalum nitride layer.    The solar cell of claim 2, wherein the third tantalum nitride layer has a hydrogen content that is less than a hydrogen content of the second tantalum nitride layer.    The solar cell of claim 1 or 3, wherein the first tantalum nitride layer has a refractive index smaller than a refractive index of the second tantalum nitride layer.    The solar cell of claim 4, wherein the third tantalum nitride layer has a refractive index smaller than a refractive index of the second tantalum nitride layer.    The solar cell of claim 5, wherein the first and third tantalum nitride layers have a refractive index of less than 2, and the second tantalum nitride layer has a refractive index greater than 2.4.    The solar cell of claim 1 or 3, wherein the second tantalum nitride layer comprises first and second tantalum nitride films; the passivation layer further comprises a buffer layer, the buffer layer comprising a third And a fourth and fifth tantalum nitride film; and the first tantalum nitride layer, the third tantalum nitride film, the first tantalum nitride film, the fourth tantalum nitride film, and the second tantalum nitride The film, the fifth tantalum nitride film, and the third tantalum nitride layer are sequentially arranged.    The solar cell of claim 7, wherein the third, fourth and fifth tantalum nitride films have a refractive index smaller than a refractive index of the first and second tantalum nitride films.    The solar cell of claim 8, wherein the first and third tantalum nitride layers have a refractive index smaller than a refractive index of the third, fourth and fifth tantalum nitride films.    The solar cell of claim 9, wherein the first and third tantalum nitride layers have refractive indices of less than 1.9, and the third, fourth and fifth tantalum nitride films have a refractive index of 1.9. And 2.4, and the first and second tantalum nitride films have a refractive index greater than 2.4.    The solar cell of claim 9, wherein the passivation layer further comprises a fourth tantalum nitride layer, the fourth tantalum nitride layer being disposed outside one of the third tantalum nitride layers, and the first The germanium content of the hafnium nitride layer is greater than the germanium content of the first, second and third tantalum nitride layers.    The solar cell of claim 11, wherein the fourth tantalum nitride layer has a refractive index greater than 2.4.    The solar cell of claim 11, wherein the passivation layer further comprises a tantalum oxynitride layer disposed outside one of the fourth tantalum nitride layers.    The solar cell of claim 13, wherein the passivation layer further comprises a tantalum oxide layer disposed between the aluminum oxide layer and the back surface of the substrate.    A solar cell comprising: a substrate having a first conductivity type, the substrate having a front surface and a back surface opposite to the front surface; an emitter layer being of a second conductivity type, the emitter layer being located in the substrate adjacent to the a front side; a back electric field layer, a first conductivity type, the back electric field layer is located in the substrate near the back surface; an anti-reflection layer is located at the front surface; an aluminum oxide layer is located at the back surface; a passivation layer The first tantalum nitride layer, the second tantalum nitride layer and a third tantalum nitride layer are sequentially arranged, wherein the first and third tantalum nitride layers have refractive indices smaller than the second nitrogen a refractive index of the ruthenium layer, and the first tantalum nitride layer contacts the aluminum oxide layer; a front electrode passes through the anti-reflection layer and contacts the emitter layer; and a back electrode passes through the passivation layer and The aluminum oxide layer is in contact with the back electric field layer.    A solar cell comprising: a substrate having a first conductivity type, the substrate having a front surface and a back surface opposite to the front surface; an emitter layer being of a second conductivity type, the emitter layer being located in the substrate adjacent to the a front side; a back electric field layer, a first conductivity type, the back electric field layer is located in the substrate near the back surface; an anti-reflection layer is located at the front surface; an aluminum oxide layer is located at the back surface; a passivation layer The first tantalum nitride layer, the second tantalum nitride layer and the third tantalum nitride layer are sequentially arranged, wherein the first and third tantalum nitride layers have hydrogen contents smaller than the second nitrogen a hydrogen content of the ruthenium layer, and the first tantalum nitride layer contacts the aluminum oxide layer; a front electrode passes through the anti-reflection layer and contacts the emitter layer; and a back electrode passes through the aluminum oxide layer And the passivation layer and contacting the back electric field layer.