When people think about solar energy materials, they often mean crystalline silicon (c-Si) cells, the most popular solar technology. Many don’t realise that thin film solar cells are another excellent option for converting visible light into useable power output.

Professor Karl Böer discovered the potential for combining thermal collectors and thin film photovoltaic cells in 1970. By 1986, the first commercial thin film technologies became available to the public. Below we discuss everything you need to know about thin film technology and solar panels.

What Are Thin Film Solar Cells and How Do They Work?

Thin film solar cell technology is a second-generation evolution from c-Si modules made by applying one or several layers of thin photovoltaic materials atop different elements, like glass, metal, plastic, or a combination of each. The thin layers allow for more flexible and lightweight applications compared to the first-generation c-Si technology.

While thin film solar panels use less semiconductor material during manufacturing, they still rely on photovoltaic (PV) energy. The electrons inside the thin film PV module’s semiconductor shift positions, creating a harnessable electric flow that an external circuit can convert into useable electricity.

Thin film panels typically offer lower costs and less efficiency than c-Si models. Thin film solar efficiency directly depends on the materials, including the growth technology and semiconductor. While they do not have a reputation for offering high-efficiency outputs, recent technological strides show the potential that thin film solar modules provide.

In December 2015, the world’s largest CIS solar energy provider, Solar Frontier, set a new record for thin film solar module efficiencies, achieving a 22.3% conversion efficiency [1]. The company aims to achieve 30% soon.

What Is Used in Thin film Solar Cells?

Thin film solar cells require a very thin layer of PV materials atop an element that absorbs light. Light-absorbing layers commonly include cadmium telluride, copper indium gallium selenide, amorphous silicon, and gallium arsenide.

Thin film solar cell materials offer reduced ecological impacts when considering all manufacturing stages compared to crystalline silicon panels [2].

Certain materials involve much more complicated manufacturing than others. For example, permanent applications might require different materials than portable models, and large-scale commercial operations differ greatly from home rooftop needs. Below, we discuss the specific element requirements and manufacturing steps for the most common layering materials.

Why Is Thin Film Used in Solar Cells?

Developers may opt for a thin film solar panel to reduce costs, use less material, and create less waste. These solar panels are easier to manufacture, reducing time limitations and excessive expenses.

You also have more versatility when choosing thin film technologies over the first-generation c-Si option. With the decreased weight and increased flexibility, commercial contractors can apply the cells between window panes or laminate the thin film panel directly on the glass. Additional applications include portable calculators, vehicles, and more.

The Different Types of Thin Film Solar Technology

Thin film solar panels work well across different materials to meet the needs of various commercial applications. Below, we explain the advantages and disadvantages of each.

Cadmium Telluride (CdTe)

CdTe panels rely on two absorber layers, p-doped Cadmium Telluride and n-doped CdS, which combine to create a p–n heterojunction. Above this layer, the CdTe cells use fluorine-doped tin oxide and zinc telluride with a paste substrate to form a Transparent Conductive Oxide layer. CdTe technology usually requires either:

• Vapor-transport deposition
• Closed-space sublimation deposition

The current top efficiency level reached under Standard Testing Conditions using CdTe panels is 19%, which is 3.1% beneath the top single solar cell achievements [3]. Calcium telluride boasts a 5.1% worldwide market share, making it the most widely used material for thin film applications.

Copper Indium Gallium Selenide (CIGS)

Copper selenide thin film panels use a molybdenum electrode layer over the substrate (usually metal foil or polyimide) with a sputtering process. CIGS thin film manufacturers also rely on a p-n heterojunction, combining a p-doped layer (made of CIGS cells) on top of an electrode. CIGS panels require the formation of a CdS n-doped buffer through a chemical-bath deposition.

Copper Indium Gallium Selenide (CIGS) thin film solar cells boasted a record-breaking 23.3% efficiency in 2019, with the theoretical ability to increase efficiency to 33% [4].

Amorphous Silicon (a-Si)

Amorphous silicon (a-Si) solar cells use a p-i-n or n-i-p configuration instead of an n-p heterojunction by adding an intrinsic semiconductor. The main design configurations for silicon cells include:

• Amorphous silicon
• Microcrystalline silicon tandem cells
• Polycrystalline silicon on top of a glass surface

These a-Si thin film modules don’t offer high efficiencies and cost more than other options, with a maximum efficiency of only 14% [4].

Gallium Arsenide (GaAs)

Gallium arsenide thin film cell technology requires more complex manufacturing steps that involve growing the GaAs buffers in Si substrates through different chemical and temperature alterations. Next, manufacturers fabricate the solar cell and bond it to the electrode before assembling the layers. The final top contact layer of Pt/Titanium requires electron beam evaporation.

The long and complicated manufacturing process and increased costs make this material less accessible. Considering the maximum 29.1% efficiency, this investment usually only gains attention from larger organisations [4].

Thin Film Solar Panels and Crystalline Silicon Solar Panels

Thin film solar panels and crystalline silicon solar panels differ in many ways. Crystalline silicon solar panels are the first generation of solar power technology, while thin film cells are the evolved second generation. Regarding performance, c-Si panels display greater reactivity to temperature variations, showing increased thermal PV losses, making them the better choice for extremely hot climates.

Another key difference is the balance between efficiency and cost. Some thin film materials offer a low cost, but the efficiency also drops. GaAs thin film panels might display the best efficiency levels out of all the options, though they’re the most expensive and inaccessible, making them only obtainable for space applications.

Crystalline silicon solar panels are popular because they offer an appropriate balance between affordable pricing and efficient results. These panels are usually the most suitable choice for commercial, industrial, utility, and residential needs.

When looking to save money on thin film solar panels, residential contractors usually consider one of the cheaper material options, as they require a much lower upfront investment. CdTe offers an excellent balance between cost and efficient results.

The Applications of Thin film Solar Panels

While c-Si panels hold the largest market share amongst residential and commercial users, thin film solar panels also corner different unique market areas. The most typical applications include portable vehicles, rooftops, and large-scale needs. The following use cases are not the only possible applications; they’re just the most popular.

Portable Thin Film Solar Panel

Thin film technology weighs less and is much smaller than some other options, making it perfect for portable on-the-go use cases. The most common place we see portable panels is in calculators, though recently, increased developments show more potential opportunities. For example, companies could use portable thin film solar panels in laptops, banks, remote locations, and more.

The portable application is one of the most accessible options for individual buyers wishing to purchase low-cost products with solar-powered energy.

Rooftop

People often install flexible PV modules on top of vehicles, like buses, RVs, boats, and more. Since these solar panels are thinner, installers can apply them to curved surfaces commonly found at the top of vehicles. The panels remain nearly invisible from ground level, so consumers can maintain their cars’ appearances while improving their practicality.

Typically, since rooftop applications are quite small and only involve a few panels, anyone can purchase with low upfront investment costs.

Large Scale

Big organisations also occasionally use thin film solar technology for large-scale purposes. These panels are durable and degrade very slowly, potentially offering a better long-term investment. As the manufacturing process becomes cheaper, some predict this underdog will take over the solar power industry.

The best example of large-scale thin film applications is in outer space advancements. The lightweight technology offers ideal temperature and damage resistance for the extreme conditions found in space.

Thin Film Solar Cell Final Thoughts

We’ve seen enormous strides in solar panel technology in recent years. Today, commercial and residential contractors have many materials to choose from, depending on their budget and application needs. Thin film solar cells may not be the most popular option today, though considering their flexibility, application ranges, and potential efficiencies, they could become the next industry standard.

Understanding the physics and science behind how these technologies work is complicated. If you’d like to continue learning about thin films, we invite you to browse through more articles from the Korvus Technology blog.