PERC technology: the new generation of photovoltaic cells

If you follow the photovoltaic market, you may have already heard about PERC technology. The main manufacturers of photovoltaic modules use this technology in the latest generations of their products, with efficiencies that exceed 19%.

Basically, PERC technology consists of thinner photovoltaic cells manufactured with an additional layer of passivation, which we will explain below. As advantages, PERC technology allows obtaining photovoltaic cells with less use of raw materials (cheaper) and high efficiency.

Crystalline silicon

Crystalline silicon (c-Si), in poly or multicrystalline (also known as polycrystalline) forms, dominates the photovoltaic cell market, with more than 90% of the market share compared to other technologies, including thin films and other semiconductor materials.

Much of the cost of manufacturing crystalline photovoltaic cells and modules lies in the process of obtaining wafers of silicon. Costs associated with the quantity of raw materials and the use of energy in the manufacture of wafers They are the great villains of the crystalline silicon industry.

Recently, advances have been made in the manufacture of wafers with the introduction of the diamond wire sawing method. This method makes it possible to obtain 50% more wafers than traditional methods, with the same amount of raw material.

This means that wafers thinner can typically be obtained with thicknesses less than 200 micrometers (1 micrometer is equal to 1 thousandth of a millimeter). The immediate consequence of this is the reduction in the prices of photovoltaic cells and modules for the consumer market.

But not everything is perfect. Reducing the thickness of the silicon cells reduces the conversion efficiency, since the recombination rates of electrons and holes become higher (a subject that we will explain in another article).

PERC technology

The meaning of the acronym PERC varies depending on the source consulted. Authors refer to it as Passivated Emitter Rear Cell, Passivated Emitter Rear Contact or Passivated Emitter and Rear Cell.

All these denominations have more or less the same meaning. Regardless of the name used, let's try to understand how it works.

PERC technology represents a major industry advancement beyond traditional crystalline cells. The technology, however, is not new – it was developed more than 30 years ago at the University of South Wales, in Australia, but has only now begun to be used commercially.

For a long time, manufacturers were focused on improving the manufacturing processes of traditional crystalline cells and technologies such as PERC, for one reason or another, remained in the refrigerator.

The recent interest in the PERC technique was largely motivated by aggressive competitiveness among manufacturers of photovoltaic cells and modules.

Manufacturers continually try to improve their products, using all possible devices and technologies to achieve greater efficiencies.

In the following figures we find a comparison between the structures of a conventional cell and a PERC cell. The big difference between the two is the presence of a very thin passivation layer on the back.

Passivation allows the cell's efficiency to be increased by reducing the electron recombination speed on the silicon surface.

In addition to this electrical property, passivation also has an optical effect that allows light to be reflected at the bottom of the cell, causing solar rays to pass through the silicon more often, increasing the capture of energy from solar radiation.

PERC technology has gained great interest from global manufacturers. In 2017 alone, more than 15 GW of PERC modules were manufactured. The reason for this is that a PERC cell manufacturing line requires the addition of only two processes to traditional cell manufacturing lines.

Thus, manufacturers can quickly and with low investment manufacture PERC cells that are more efficient than conventional non-passivated crystalline silicon cells. The market has absorbed the technology well and PERC modules are now commercially available on a large scale.

Commercial PERC modules

Below is an example of a commercial product using PERC monocrystalline cell technology, simply known as MONO PERC on the market. Efficiencies range from 17.7% to 19.2%.

References

• Surface Recombination Velocity of Local Al-contacts of PERC Solar Cells Determined from LBIC Measurements and 2D Simulation, Energy Procedia, Volume 92, 2016, p. 82-87
• Surface Passivation of Crystalline Silicon Solar Cells – A Review, PROGRESS IN PHOTOVOLTAICS] RESEARCH AND APPLICATIONS, Volume 8, 2000, p. 473-487
• Advances in surface passivation of c-Si solar cells, Materials for Renewable and Sustainable Energy, 12/2012
• Electric Field Effect Surface Passivation for Silicon Solar Cells, Solid State Phenomena, 205-206, 346, Proceedings of XV GADEST
• Stable Field Effect Surface Passivation of n-type Cz Silicon, Energy Procedia, Volume 38, 2013, p. 816–822
• Momentum builds for HJT, PV Magazine, 09/2017
• Panel predictions 2018, PV Magazine, 11/2017
• Study on PID resistance of HIT PV modules, Photovoltaic Module Reliability Workshop NREL, 2013
• Heterojunction cell technology of Meyer Burger: Production processes and measuring methods, Matthias Seidel, Roth & Rau AG, Hohenstein-Ernstthal, Germany, & Rajesh Ambigapathy, Pasan SA, Neuchâtel, Switzerland
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• Solar Cells and Arrays: Principles, Analysis, and Design, Abdelhalim Zekry, Ahmed Shaker, Marwa Salem
• Panasonic HIT Heterojunction technology, https://eu-solar.panasonic.net/en/hit-heterojunction-sanyo-panasonic.htm
• PERC cell technology explained, https://www.aleo-solar.com/perc-cell-technology-explained/
• The Passivated Emitter and Rear Cell (PERC): From conception to mass production, Solar Energy Materials and Solar Cells, Volume 143, 2015, p. 190-197