Preparation of Solar Cells by Lighting Method Improves Battery Output Power

To make solar cells, it is necessary to make the silicon wafer temperature exceed 1000 °C. This process usually requires heating elements that consume a lot of energy.

A new optical oven has been developed. At the National Renewable Energy Laboratory in Golden, Colorado, researchers heat solar wafers to gather light rays and align them. This is a more efficient process that consumes about half the energy of a conventional stove. More importantly, this new design also uses light to remove certain impurities from the silicon wafer. This step can increase the output power of the finished battery.

This furnace uses a light bulb instead of a heating element to process silicon wafers.

The study is in its early stages. So far, researchers have only increased their efficiency. The efficiency of solar cells made has only increased by half a percentage point. However, according to laboratory tests, they believe that they can increase their efficiency by four percentage points, from an efficiency of about 16% to 20%, which is a major event in the solar industry, and the industry will even celebrate a half-percentage increase.

High temperatures are needed, and they are needed in more than one step. This is how solar cells are made. The furnace is used to incorporate dopants into the silicon, creating an electric field within the material, creating electrical contact, and oxidizing the surface to increase efficiency. This new furnace can also better control these processes and increase the efficiency of solar cells.

It is not only the design of the National Renewable Energy Laboratory that uses light-processed silicon. Rapid heat treatment furnaces are used in the microelectronics industry and also use light to heat semiconductors. However, this new furnace uses highly reflective, heat-resistant ceramics to ensure that only the silicon wafer absorbs light and the furnace walls do not absorb light. "This will increase its efficiency many times," said Bhushan Sopori, a researcher at the National Renewable Energy Laboratory who is responsible for this type of furnace project.

By accurately designing the internal shape of the furnace, researchers can precisely control the light gathering position and ensure that the wafer is heated evenly. This is still not enough to ensure that the wafers are uniformly illuminated and the edges must receive more light because they dissipate heat faster than other parts of the wafer.

This process reduces the thermal stress on the wafer and allows precise control of heat-induced chemical reactions. Accurate control of the heating rate and time can also improve the electrical contacts of solar cells and improve efficiency. This can indeed initiate the oxidation step. Oxidation is usually used by only a few manufacturers for high-end solar cells, but this new process will be cheaper and will allow more manufacturers to use it.

Soperrey said that the National Renewable Energy Laboratory has developed some processes that can better utilize the photon effect and outperform the rapid heat treatment furnace. Because photons interact with silicon, it can cause harmful impurities such as iron to flow out of the material, while retaining some useful components, such as boron, which are required for normal operation of solar cells.

Researchers have not yet increased efficiency by a full four percentage points, in part because the new processing steps are not fully compatible with the other steps of traditional manufacturing. Sopelri said they are working hard to improve other steps to take full advantage of this furnace.

The National Renewable Energy Laboratory has also teamed up with Advanced Optical Systems to develop a machine that can process more than 2,000 wafers at a time, just like a laboratory version. This high output is necessary because the stove is to compete with traditional stoves, and traditional stoves are cheaper to run.