# US 2013/0153019 A1 · Methods of forming a high efficiency solar cell with a localized back surface field

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- Number: US 2013/0153019 A1
- Document ID: US20130153019A1
- Status: Published application
- Kind: A1
- Application number: 13/687,126
- Filed: 2012-11-28
- Published: 2013-06-20
- Earliest claimed: 2011-12-20
- Assignees: Innovalight, Inc.
- Inventors: KARIM LOTFI BENDIMERAD; DANIEL ANEURIN INNS; DMITRY POPLAVSKYY
- Web page: https://patentgrep.com/patent/US20130153019A1

## CPC

- H10F 77/315: {the coatings being antireflective or having enhancing optical properties}
- H10F 10/14: Photovoltaic cells having only PN homojunction potential barriers
- H10F 71/121: {The active layers comprising only Group IV materials}
- H10F 71/128: {Annealing}
- Y02E 10/547: Monocrystalline silicon PV cells
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A solar cell, comprising: a doped silicon substrate, the silicon substrate comprising a front surface and a rear surface; a front phosphorous diffusion layer formed on the front surface; a front anti-reflective layer formed on the front phosphorous diffusion layer; a front metal electrode on the front surface in ohmic contact with the front phosphorous diffusion layer through the front anti-reflective layer; a rear passivation layer formed on the rear surface; a rear metal electrode in a pattern on the rear surface passing through the rear passivation layer; and a rear p+ diffusion area on the rear surface between the rear passivation layer and a boron-doped region of the silicon substrate, the rear p+ diffusion area surrounding the rear metal electrode.

## Claims

### Claim 1

A method of forming a high efficiency solar cell, comprising steps of:
(a) providing a doped silicon substrate, the substrate comprising a front surface and a rear surface;
(b) depositing an ink on the rear surface in a pattern, the ink comprising a p-type dopant and a solvent;
(c) heating the silicon substrate in a baking ambient to a first temperature and for a first time period in order to remove residual solvent from the deposited ink;
(d) heating the silicon substrate in a diffusion ambient to a second temperature and for a second time period in order to diffuse the p-type dopant into the rear surface to form a rear p+ diffusion area on the rear surface;
(e) exposing the silicon substrate to a phosphorous deposition ambient at a third. temperature for a third time period, wherein a front PSG layer and a front phosphorous diffusion layer are formed on the front surface;
(f) exposing the silicon substrate to an etchant for a third time period, wherein the front PSG layer is substantially removed;
(g) depositing a front anti-reflective layer on the front surface and a rear passivation layer on the rear surface; and
(h) forming a front metal electrode on the front surface in ohmic contact with the front phosphorous diffusion layer through the front anti-reflective layer and a rear metal electrode on the rear surface through the rear passivation layer, the rear metal electrode being formed on the rear p+ diffusion area on the rear surface.

### Claim 2 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein a rear PSG layer and a rear phosphorous diffusion layer are formed on the rear surface during the step (e), and wherein the rear PSG layer is substantially removed during the step (f).

### Claim 3 (depends on 2)

A method of forming a high efficiency solar cell according to claim 2, further comprising a step of removing the rear phosphorous diffusion layer, wherein a silicon in a part of the rear phosphorous diffusion layer where the ink was not deposited is selectively removed for between 0.05 and 5 μm.

### Claim 4 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the rear surface is covered during the step (d) to prevent the rear surface from being exposed to the phosphorous deposition ambient.

### Claim 5 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the step (e) is applied prior to the step (d).

### Claim 6 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein a pre-diffusion cleaning step is applied after step (c).

### Claim 7 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, further comprising a step of depositing an ink comprising silicon nanoparticles dispersed in a solvent on the front surface in a pattern prior to the step (e).

### Claim 8 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the p-type dopant is a boron-containing material.

### Claim 9 (depends on 8)

A method of forming a high efficiency solar cell according to claim 8, wherein the boron-containing material is selected from the group consisting of boron (B), boron nitride (BN), boron oxide (B2O3), boric acid (B(OH)3), boron carbide (B4C), boron silicide (B2Si, B3Si, B4Si, B6Si), boron-doped group TV nanoparticles, aluminum boride (AlB2), barium boride (BaB6), calcium boride (CaB6), cerium boride (CeB6), chromium boride (CrB), cobalt boride (Co2B—Co3B), dysprosium boride (DyB4, DyB6), erbium boride (ErB4), europium boride (EuB6), gadolinium boride (GdB6), hafnium boride (HfB2), holmium boride (HoB4), iron boride (Fe2B), lanthanum boride (LaB6), lutetium boride (LuB4), magnesium boride (MgB2), manganese boride (MnB, MnB2), molybdenum boride (MoB), neodymium boride (NdB6), nickel boride (NiB), niobium boride (NbB2), praseodymium boride (PrB6), rhenium boride (Re7B3), samarium boride (SmB6), scandium boride (ScB2), strontium boride (SrB6), tantalum boride (TaB2), terbium boride (TbB6), thulium boride (TmB4), titanium boride (TiB2), tungsten boride (WB, W2B, W2B5), vanadium boride (VB2), ytterbium boride (YbB6), and zirconium boride (ZrB2, ZrB12).

### Claim 10 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the ink further comprises a ceramic particle and a polymer binder, and wherein the p-type dopant and the ceramic particle are dispersed in the solvent.

### Claim 11 (depends on 10)

A method of forming a high efficiency solar cell according to claim 10, wherein the ceramic particle is selected from the group consisting of SiN, SiO2, SiC, TiO2, Al2O3, MgO, CaO, Li2O, BeO, SrO, Sc2O3, Y2O3, La2O3, CeO2, Ce2O3, Pr2O3, Nd2O3, Sm2O3, EuO, Gd2O3, Ta2O5, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, ThO2, UO2, ZrO2, and HfO2.

### Claim 12 (depends on 10)

A method of forming a high efficiency solar cell according to claim 10, wherein the p-type dopant is between 0.5 and 20 wt %, the ceramic particle is between 3 and 50 wt %, the polymer binder is between 0.5 and 3 wt %, based on the total weight of the ink.

### Claim 13 (depends on 12)

A method of forming a high efficiency solar cell according to claim 12, wherein the p-type dopant is between 1 and 10 wt %, the ceramic particle is between 5 and 30 wt %, the polymer binder is between 0.75 and 2 wt %, based on the total weight of the ink.

### Claim 14 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the anti-reflective layer and the rear passivation layer comprise SiNx.

### Claim 15 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the second temperature is between 875° C. and 950° C., and the ambient is nitrogen, oxygen, or mixture thereof.

### Claim 16 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the second time is between 20 minutes and 60 minutes.

### Claim 17 (depends on 1)

A method of forming a high efficiency solar cell according to claim 1, wherein the silicon substrate is doped with boron atoms.

### Claim 18

A solar cell, comprising:
a doped silicon substrate, the silicon substrate comprising a front surface and a rear surface;
a front phosphorous diffusion layer formed on the front surface;
a front anti-reflective layer formed on the front phosphorous diffusion layer;
a front metal electrode on the front surface in ohmic contact with the front phosphorous diffusion layer through the front anti-reflective layer;
a rear passivation layer formed on the rear surface;
a rear metal electrode in a pattern on the rear surface passing through the rear passivation layer; and
a rear p+ diffusion area on the rear surface between the rear passivation layer and a boron-doped region of the silicon substrate, the rear p+ diffusion area surrounding the rear metal electrode.

### Claim 19 (depends on 18)

A solar cell of claim 18, further comprising a rear phosphorous diffusion layer formed between the rear passivation layer and the boron-doped region of the silicon substrate, wherein the rear p+ diffusion area prevents the direct contact of the rear metal electrode with the rear phosphorous diffusion layer.

### Claim 20 (depends on 18)

A solar cell of claim 18, wherein the rear passivation layer is in direct contact with the boron doped region of the silicon substrate, wherein the rear p+ diffusion area prevents the direct contact of the rear metal electrode with the interface between the rear passivation layer and the boron-doped region of the silicon substrate.

### Claim 21 (depends on 18)

A solar cell of claim 18, wherein the rear p+ diffusion area is boron-doped.

### Claim 22 (depends on 18)

A solar cell of claim 18, wherein the rear p+ diffusion area is formed between the rear metal electrode and the boron-doped region of the silicon substrate and wherein the rear metal electrode on the rear surface is not in direct contact with the boron-doped region of the silicon substrate.

### Claim 23 (depends on 18)

A solar cell of claim 18, wherein the rear passivation layer comprises SiNx.

### Claim 24 (depends on 18)

A solar cell of claim 18, wherein the substrate is doped with boron.