Thin-film solar panels are among the most advanced and efficient power generation technologies created for the solar industry. These photovoltaic (PV) modules include several types according to the materials used to manufacture them. One of the most popular ones is the Copper Indium Gallium Selenide (CIGS) technology.
In this article, we cover the basics of CIGS technology. We do a deep analysis on what is CIGS technology, the manufacturing process, and the materials used for it, we also compare CIGS solar cell efficiency and the technology in general against Crystalline Silicon (c-Si) and other thin-film technologies. If you want to understand and know more about CIGS technology, this article is for you.
Basics: What are CIGS thin-film solar panels?
The CIGS thin-film solar panel is a variety of thin-film modules using Copper Indium Gallium Selenide (CIGS) as the main semiconductor material for the absorber layer. This technology is being popularized for utility-scale installations, Building-Integrated Photovoltaics (BIPV), PV rooftops, flexible thin-film solar panels, and more.
While thin-film technology was first developed in 1972 by Prof. Karl Böer, it was not until 1981 when CIGS technology was created. The precursor of the CIGS solar cell was the Copper Indium Selenide (CuInSe2 or CIS) cell created by The Boeing Company with a 9.4% efficiency. In 1995, researchers from the National Renewable Energy Laboratory (NREL) embedded Gallium into the CIS matrix and created the first CIGS solar cell with an efficiency of 17.1%.
CIGS thin-film solar panels generate power like other PV modules under the photovoltaic effect. The CIGS solar cell created with CIGS and Cadmium sulfide (CdS) for the absorber, generates power by absorbing photons from incoming sunlight, producing electrons that travel from the n-side to the p-side of the junction in the absorber layer.
All the aforementioned process generates an electric current harnessed by the circuitry designed around the CIGS thin-film solar panel. This current can power a load, be stored in batteries, or sent to the grid and be accounted for by the Net Metering system.
The materials and manufacturing process of CIGS solar cells
Like many other thin-film solar panels, CIGS PV modules are manufactured using four vital layers:
- Protective layer
- Photovoltaic material
- Conductive sheet
Each layer in the CIGS thin-film solar panel either plays a vital role in the solar energy conversion process or defines the application for the module.
There are different processes used in the manufacture of CIGS solar cells, some include Direct-Current (DC) sputtering which is a variation of physical vapor deposition (PVD), Chemical Bath Depositions (CBD), Chemical Vapor Deposition (CVD), or co-evaporation processes.
The materials used in each layer of the manufacturing process for the CIGS solar cell are the following:
The protective layer is called Transparent Conductive Oxide (TCO) layer. This layer protecting the CdS buffer from external damage is placed in the cell through sputtering or CVD. The TCO layer is manufactured with Intrinsic Zinc Oxide (i-ZnO) placed over the CdS buffer, and then covered with an AZO compound layer made of Aluminum doped Zinc Oxide (Al: ZnO).
Photovoltaic material or absorbing layer
The photovoltaic material is the heart of the CIGS solar cell. This is a p-n heterojunction manufactured by placing a p-type layer made from copper indium gallium selenide (CIGS) through co-evaporation and a p-type layer of Cadmium sulfide (CdS) deposited by CBD on top of the CIGS.
The back contact or conductive sheet is directly placed on top of the substrate, before placing the photovoltaic material. This layer is made by placing molybdenum (Mo) through DC sputtering, resulting in a highly reflective and conductive film working as the main contact for the cell.
The substrate is the backbone of the CIGS solar cell. This is the first layer where the rest of the materials are placed, defining the flexibility and other properties of the cell. Varying on the desired properties for the module, substrate for CIGS solar cells can be manufactured with glass, a polymer called polyimide, or a metal foil of titanium, stainless steel, or a similar material.
How do CIGS thin-film panels stack up against traditional crystalline panels?
Crystalline Silicon (c-Si) is the most popular and widely sold PV technology with a 90.9% global market share, while CIGS holds 2.0% of the retail PV market. To have a deeper insight and knowledge about CIGS technology, it is important to compare both of them.
One important difference between these technologies is the efficiency and how it is affected by temperature. The highest recorded efficiency for mono c-Si and poly c-Si technologies is set at 26.7% and 24.4% respectively, while the CIGS solar cell achieved a recorded efficiency of 23.4%.
The c-Si technology represents higher losses due to temperature changes, with a temperature coefficient of -0.446%/ºC and -0.387%/ºC for mono c-Si and poly c-Si respectively, while CIGS technology has a temperature coefficient of -0.36%/ºC.
The major difference making c-Si technology more popular and widely used is the price. The cost per watt for mono c-Si can oscillate between $0.16-$0.46, and $0.24/W for poly c-Si. CIGS technology is much more expensive, with a cost of 0.60$/W.
While c-Si technology is cheaper, CIGS still has several advantages in favor. CIGS represents fewer power losses because it is more sensitive to light, resulting in modules generating more power than c-Si modules under low irradiance conditions. CIGS technology also has more versatile applications, being used for solar shingles, BIPV, flexible PV modules, while c-Si technology is mainly used for rooftop applications and solar farms.
CIGS thin-film vs. Other types of thin-film solar technologies
CIGS technology is among the thin-film solar technologies. Each of these technologies has different technical parameters, costs, and other characteristics that make them unique, and in most cases, better suited for certain applications. In this section, we compare the CIGS against the other thin-film technologies to analyze how they differ from one another.
CIGS vs. Other Thin-film Technologies
|Solar Cell Technology||Copper Indium Gallium Selenide (CIGS)||Cadmium Telluride (CdTe)||Amorphous Silicon (a-Si)||Gallium Arsenide (GaAs)|
|Highest Recorded Efficiency||23.4%||22.1%||14.0%||29.1%|
|Performance at Low Irradiance||84%||99%||91%||85%|
|The Lifespan of the PV Module||25 years||30 years||10-25 years2||30 years|
|Applications||Commercial / Industrial||Commercial / Industrial||Mostly Building-Integrated Photovoltaics||Mostly space applications|
2 Depending on the location and manufacturer.
While GaAs technology holds the highest solar conversion efficiency, CIGS solar cell efficiency has the highest conversion rate under a decent price (less than 0.7$/W). Even though CIGS solar cell efficiency is higher than CdTe, the manufacturing cost is also higher, causing CdTe technology to hold 5.1% of the retail market while CIGS technology only holds 2.0% of it.
CdTe and CIGS technologies are used in commercial and utility-scale applications. Both technologies have a long lifespan, and are less affected by temperature compared to Crystalline Silicon technology. The only downside is their relatively higher cost compared to c-Si technology.
Typical applications of CIGS thin-film solar panels
With high recorded efficiency, CIGS technology is becoming quite popular due to its applications. In this section, we analyze some of the most common applications for the technology.
Solar shingle tiles
CIGS solar technology is used to manufacture solar shingle tiles, which are CIGS solar cells capsuled within durable and lightweight polymer sheets, giving the shingle its shape and color. Solar shingle tiles can provide homes with high-quality architectural designs the possibility of generating solar power without installing the regular rooftop PV system, maintaining the aesthetics while enjoying renewable energy.
Considering the high efficiency and reduced losses due to temperature, CIGS technology is becoming more popular for utility-scale applications. Installing a CIGS solar farm might require a larger installation space than with rigid modules, but the power output, durability, and other aspects make it a better investment.
Crystalline silicon modules are the most commonly used technology for rooftop installations, but many homeowners are opting for CIGS PV modules. CIGS technology performs better in climates with extreme temperatures due to their temperature coefficient, they have a longer lifespan and perform better for different levels of solar irradiance than c-Si modules.
Building Integrated Photovoltaics
Building Integrated Photovoltaics or BIPV is one of the most cutting-edge and innovative applications of CIGS technology. This is achieved by installing colored or patterned PV modules used with CIGS technology.
This application gives buildings (especially those with high-end architectural designs) the ability to generate solar power without disrupting aesthetics. BIPV applications are extremely useful since the building takes advantage of the large façade surface to generate solar power and does not require additional space.
Flexible PV modules
CIGS technology can be used to manufacture flexible PV modules. These modules can be adapted to odd shapes, curved rooftops, or the sides of buildings, providing the ability to generate power with PV modules that adapt to the shape of the surface.
CIGS alongside and CdTe technology can be used for portable applications. This provides a method of generating small amounts of power to charge electronics and power small appliances while being on the road, camping, or doing similar activities. The two most common portable applications are foldable solar panels and solar chargers.
Looking into the future of CIGS thin-film solar technology
CIGS is among the most versatile and high-performing thin-film technologies. While it has its limitations, there are also many possibilities for its future.
CIGS technology also has the potential of reducing costs and becoming a cheap solar technology in the future. CIGS technology requires fewer materials, less energy to produce, and the manufacturing can be highly automated, requiring even fewer machines than with c-Si technology.
The CIGS solar cell efficiency can be improved even further. By addressing most aspects producing losses for the technology, CIGS solar cell efficiency can increase to a 30% conversion rate, more than the current efficiency for Crystalline Silicon cells.
There are limits regarding the manufacturing of CIGS PV modules, but this will be reduced in the future. There are large investments in place aimed to improve the technology and increase production, which will reduce the overall cost of CIGS modules in the future and increase the market share for this technology, making it even more popular in the solar industry.