SOLAR CELL WITH REDUCED SURFACE RECOMBINATION

A solar cell is provided. The solar cell includes a p-n junction and a coating. The p-n junction includes upper and lower layers. The coating overlies the upper layer of the p-n junction. The coating includes a transparent conductive layer and a gate dielectric layer, which is interposed between the transparent conductive layer and the upper layer of the p-n junction. The solar cell further includes a front-contact and a back-contact, which are electrically communicative with each other. The front-contact is electrically communicative with the upper layer of the p-n junction through the coating. The back-contact is electrically communicative with the lower layer of the p-n junction. The solar cell can also include a contact via electrically communicative with the back-contact and with the transparent conductive layer.

BACKGROUND

The present invention generally relates to solar cells. More specifically, the present invention relates to a solar cell with reduced surface recombination.

A solar or photovoltaic cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. Individual solar cells can be combined to form modules, otherwise known as solar panels. Operations of solar cells generally involve three attributes: the absorption of light to generate electron-hole pairs or excitons; the separation of charge carriers of opposite types; and the separate extraction of those carriers to an external circuit.

SUMMARY

Embodiments of the present invention are directed to a solar cell. A non-limiting example of the solar cell includes a p-n junction and a coating. The p-n junction includes upper and lower layers. The coating overlies the upper layer of the p-n junction. The coating includes a transparent conductive layer and a gate dielectric layer, which is interposed between the transparent conductive layer and the upper layer of the p-n junction. The non-limiting example of the solar cell further includes front and back contacts, which are electrically communicative with each other. The front-contact is electrically communicative with the upper layer of the p-n junction through the coating. The back-contact is electrically communicative with the lower layer of the p-n junction. The non-limiting embodiment of the solar cell further includes a contact via, which is electrically communicative with the back-contact and with the transparent conductive layer.

Embodiments of the present invention are directed to a solar cell. A non-limiting example of the solar cell includes a first layer with a first dopant type semiconductor. A second layer is over the first layer with the first dopant type semiconductor and a second dopant diffused therein. A coating is over the second semiconductor layer. The coating includes a transparent conductive layer and a gate dielectric layer, which is interposed between the transparent conductive layer and the second layer. The non-limiting example of the solar cell includes circuitry. The circuitry includes a front-contact, a back-contact and a coupling. The front-contact is electrically communicative with the second layer through the coating. The back-contact is electrically communicative with the first layer. The front- and back-contacts are electrically communicative by way of the coupling. In addition, the circuitry includes a contact via, which is electrically communicative with the transparent conductive layer, and an additional coupling by which the contact via and the back-contacts are electrically communicative.

Embodiments of the present invention are directed to a method of increasing an efficiency of a solar cell. A non-limiting example of the method includes inducing majority carrier accumulation at a surface of the solar cell to reduce a surface recombination rate of the solar cell. The inducing of the majority carrier accumulation is accomplished using a self-generated voltage of the solar cell.

In the accompanying figures and following detailed description of the described embodiments, the various elements illustrated in the figures are provided with two or three digit reference numbers. With minor exceptions, the leftmost digit(s) of each reference number correspond to the figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related to semiconductor device, integrated circuit (IC) and solar cell fabrication may or may not be described in detail herein. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. In particular, various steps in the manufacture of semiconductor devices, semiconductor-based ICs and solar cells are well known and so, in the interest of brevity, many conventional steps will only be mentioned briefly herein or will be omitted entirely without providing the well-known process details.

Turning now to an overview of technologies that are more specifically relevant to aspects of the invention, an operation of a solar cell (of a solar panel, for example) involves several steps. Initially, photons in light hit the solar panel and are absorbed by semiconducting materials, such as silicon. Electrons are then excited from their current molecular/atomic orbital and, once excited, can either recombine or travel through the solar cell to an electrode as captured electricity.

Instances in which electrons are recombined can be grouped together and define a surface recombination characteristic of a solar cell. Because the surface recombination does not involve the generation of electricity, surface recombination is a key issue that limits an efficiency of a solar cell. In addition, because surface recombination velocity is sensitive to surface majority carrier density, increasing a surface majority carrier density in a solar cell can effectively reduce surface recombination velocity and thus reduce the surface recombination characteristic of a solar cell.

Turning now to an overview of the aspects of the invention, one or more embodiments of the invention address the above-described shortcomings of the prior art by providing a method to increase majority carrier density of and an efficiency of a solar cell and by providing a solar cell with an increased efficiency.

The above-described aspects of the invention address the shortcomings of the prior art by making use of a metal-oxide-semiconductor (MOS) field effect of a solar cell. That is, when a cell solar is operating, a p-type side of the solar cell typically has a higher potential. By connecting a back-contact to a front transparent conductive oxide (TCO) layer, a positive bias can be applied to a top MOS structure. Therefore, additional electrons (beyond what would normally be generated in a solar cell of similar capacity) is induced at the top surface so that the surface recombination rate of the solar cell can be reduced. The amount of accumulated electrons available for the additional flows depends on the TCO work function, voltage of solar cell, effective oxide thickness (EOT), characteristics of the gate dielectric, etc.

Turning now to a more detailed description of aspects of the present invention,FIG. 1depicts a side view of a structure98after initial fabrication operations in accordance with aspects of the invention. The structure98depicted inFIG. 1includes a p-n junction100for use in a solar cell101(seeFIG. 7) in accordance with embodiments of the invention. The p-n junction100is formed at an interface between a first or lower layer110and a second or upper layer120. The upper layer120overlies the lower layer110. The lower layer110can be provided as a first dopant type semiconductor material, such as a p-type silicon (Si). The upper layer120is formed by diffusing a second dopant, such as an n-type dopant, into the first dopant type semiconductor material. As such, the lower layer110and the upper layer120of the p-n junction100can be formed to have an opposite polarity once formation and assembly of the solar cell101is completed.

It is to be understood that, while the lower layer110and the upper layer120are described herein as being provided as a p-type silicon (Si) and as an n-type silicon (Si) with n-type dopants, respectively, this is not required and that other doping options are available. For example, the lower layer110and the upper layer120can be provided as an n-type silicon (Si) and as a p-type silicon (Si), respectively. The following description will, however, focus on the case of the lower layer110and the upper layer120being provided as a p-type silicon (Si) and as an n-type silicon (Si), respectively, for purposes of clarity and brevity.

FIG. 2depicts a side view of the structure98ofFIG. 1after multiple layers of a coating130have been formed over the upper layer120in accordance with embodiments of the invention. The multiple layers of the coating130can include a gate dielectric layer132, a transparent conductive layer131, and an anti-reflective dielectric layer133, configured and arranged as shown. More specifically, the gate dielectric layer132is interposed between the transparent conductive layer131and the upper layer120, and the anti-reflective dielectric layer133is over transparent conductive layer131. The transparent conductive layer131can be a transparent conductive oxide (TCO) or a metal layer thin enough to let light pass through.

The multiple layers of the coating130can be formed by a known process of deposition in which the gate dielectric layer132is deposited over the upper layer120, the transparent conductive layer131is deposited over the gate dielectric layer132and the anti-reflective dielectric layer133is deposited over the transparent conductive layer131.

FIG. 3depicts a side view of the structure98after known semiconductor fabrication operations have been used to form a contact trench140. In embodiments of the invention, the contact trench140can be formed using a variety of know semiconductor fabrication operations, including, for example, an etching process executed through the multiple layers (i.e., layers133,131,132) of the coating130and into the upper layer120in accordance with embodiments of the invention.

As shown inFIG. 3, the contact trench140includes an upper portion141and a lower portion142. The upper portion141extends through the coating130and is delimited by exposed sidewalls135of the coating130. The lower portion142extends into the upper layer120of the p-n junction100and is delimited by exposed sidewalls121of the upper layer120and by an upward facing surface122of the upper layer120.

FIG. 4depicts a side view of the structure98after known semiconductor fabrication operations have been used to form sidewall spacers150along the upper portion141and the lower portion142of the contact trench140in accordance with embodiments of the invention. The sidewall spacers150serve to isolate a front-contact160(to be described below) from the transparent conductive layer131. In embodiments of the invention, the sidewall spacers150can be formed by a depositional process and can include any suitable dielectric material, including, but not limited to, silicon nitride (SiN) and silicon dioxide (SiO2).

FIG. 5depicts a side view of the structure98after known semiconductor fabrication operations have been used to fill front side contact metal having into remaining space of the contact trench140(shown inFIG. 4) between the sidewall spacers150to thus form the front-contact160. The front-contact160can include copper (Cu) or another suitable metallic material and occupies the space in the region partially bound by the sidewall spacers150. A planarization process can be applied to planarize the top surfaces of the anti-reflective dielectric layer133, the sidewalls150, and the front-contact160.

InFIG. 6, known semiconductor fabrication operations have been applied to the structure98shown inFIG. 5to form a solar cell101in accordance with embodiments of the invention. More specifically, known semiconductor fabrication operations have been used to form a contact via170and a back-contact180in accordance with embodiments of the invention. The contact via170extends through the anti-reflective dielectric layer133to be electrically communicative with the transparent conductive layer131. The back-contact180can be provided as a layer181that extends across a downward facing surface111of the lower layer110. In embodiments of the invention, the contact via170can be formed as a result of an etching process executed with respect to the anti-reflective layer133and a subsequent metallic fill of the trench (not shown) resulting from the etching process. The contact via170can include copper (Cu) or another suitable metallic material.

The back-contact180can similarly include copper (Cu) or another suitable metallic material.

It is to be understood that, although the respective formations of the front-contact160, the contact via170and the back-contact180ofFIGS. 3-6were described in a particular sequence, this sequence is not required and that other optional sequences can be used to achieve the same resulting structure shown inFIG. 6. For example, the front-contact160, the contact via170and the back-contact180can all be formed substantially simultaneously with one another.

InFIG. 7, known fabrication operations have been applied to incorporate the solar cell101into a solar-powered device720, which is configured and arranged to enable the solar cell101to convert received light to electricity and provide the electricity to a load220. The solar-powered device720includes the solar cell101communicatively coupled through various coupling structures (e.g.,190,191,192,193,200,201,202) to the load220.

The coupling190provides for electrical communication between the front and back contacts160and180and includes a positive electrode lead191electrically connected to the back-contact180, a negative electrode lead192electrically connected to the front-contact160, and a circuit element193electrically connected at opposite ends thereof to the positive and negative electrode leads191and192, respectively. The additional coupling200provides for electrical communication between the back-contact160and the contact via170and includes an additional negative electrode lead201, which is electrically connected to the contact via170, and an additional circuit element202, which is electrically connected at opposite ends thereof to the positive electrode lead191and the additional negative electrode lead201, respectively.

The coupling190and the additional coupling200and their respective positive and negative electrode leads191,192and201and their respective circuit elements193and202cooperatively form circuitry210for the solar-powered device720. In accordance with some embodiments of the invention, the circuitry210can further include the load220, which is electrically interposed between the back-contact180and the front-contact160.

During operations of the solar cell101in the solar-powered device720ofFIG. 7, the circuitry210effectively provides for an operational solar cell and for a biased MOS capacitor structure700that increases an efficiency of the operational solar cell. The operational solar cell is provided for by junction region701being defined at an interface of the lower and upper layers110and120and as a result of the electrical communication between the back-contact180(i.e., the positive output terminal or the p-type silicon (Si) layer) and the front-contact160(i.e., the negative output terminal or the n+ layer) by way of coupling190. The bias voltage is provided or generated as a result of the electrical communication between the back-contact180and the contact via170(i.e., transparent conductive layer131) by way of the additional coupling200. The biased MOS capacitor structure700causes a majority carrier, such as electrons, to accumulate due to field effects in an accumulation layer702at the interface of the upper layer120and the coating130. This will lead to a reduced rate of surface recombination and a correspondingly increased solar cell efficiency.

In operation, the solar-powered device720converts light to electricity/power in the following manner. Light shines from the top the device and passes through the anti-reflective dielectric layer133, the transparent conductive layer131and the gate dielectric layer132to reach the semiconductor region. The light-generated minority carriers (electrons in p-type semiconductor and holes in n-type) diffuse towards the p-n junction100and, once there, are collected to become useful current to drive the load220. Those minority carriers that recombine at the top semiconductor surface cannot be collected and are therefore wasted. With the majority carrier accumulation at the top surface (enabled in this invention), such recombination is reduced, and more useful current can be collected.

With reference toFIG. 8, a method of reducing surface recombination in the solar cell101is provided. As shown inFIG. 8, the method includes coating the upper layer120of the p-n junction100with transparent conductive layer131and the gate dielectric layer132(block801). The method further includes forming the front-contact160to electrically communicate with the upper layer120through transparent conductive layer131and the gate dielectric layer132(block802) and forming the back-contact180to electrically communicate with the lower layer110(block803). In addition, the method includes coupling the front- and back-contacts160and180to electrically communicate with each other (block804). The method also includes forming the contact via170to electrically communicate with the transparent conductive layer131(block805) and coupling the back-contact160with the contact via170to electrically communicate with each other to thus accumulate electrons at the accumulation layer702(block806).

The term “conformal” (e.g., a conformal layer) means that the thickness of the layer is substantially the same on all surfaces, or that the thickness variation is less than 15% of the nominal thickness of the layer.