The photovoltaic (PV) industry is led by traditional rigid crystalline silicon (c-Si) technology, featuring high efficiency, low price and higher availability, but this is not the only available option. Thin-film solar technology includes many features that make it unique for particular applications that are not suited for traditional c-Si PV modules.
There are many popular thin-film solar technologies available in the market, including Gallium Arsenide (GaAs), Cadmium Telluride (CdTe), and others, with new ones being researched and developed.
In this article, you will learn about the most important thin-film solar technology, its applications, advantages and disadvantages, and other interesting facts about the technology.
What are thin-film solar panels and why are they so important to the PV industry?
Thin-film solar panel technology consists of the deposition of extremely thin layers (nanometers up to micrometers) of semiconductors on backing materials that provide the body for a PV module. These materials generate electricity from solar radiation under the photovoltaic effect.
Traditional c-Si PV modules eclipsed thin-film solar technology in the past with higher efficiency for a decent cost, but this has been pairing up in recent years. Currently, c-Si technology features a better efficiency than most thin-film solar modules for a good cost, but thin-film solar technology is particularly suited for unique applications in the PV industry that make it irreplaceable by crystalline silicon.
A clear example is Gallium Arsenide (GaAs) technology. While it features an expensive cost, its high efficiency of up to 30% in Standard Testing Conditions (STC) and 68.9% in unique lab conditions, makes it ideal for concentrated PV (CPV) and space applications. Thin-film solar technology can also be used for flexible PV modules suited for various applications, Building Integrated Photovoltaics (BIPV), portable applications, and more.
The most Popular thin-film solar panel technologies and their applications
Thin-film solar technology is a compendium of different technologies including cutting-edge technologies, popular technologies used in commercial applications, and promising technologies being developed. In this section, we explain the most important thin-film solar technologies and their applications.
Gallium Arsenide (GaAs) & Germanium (Ge): The most Popular thin-film for concentrated PV (CPV) and space applications
Gallium Arsenide (GaAs) and Germanium (Ge) are two of the most important thin-film solar technologies included in the category of multijunction III-V photovoltaics. These are complexly developed modules manufactured with several junctions instead of a single junction, designed to surpass the 33.5% Shockley-Queisser efficiency limitation set for single-bandgap solar cells.
GaAs and Ge thin-film solar cells are manufactured using Gallium and Arsenide for GaAs, and Germanium for the Ge PV modules. The III-V multijunction design in combination with the materials, increases the bandgap, resulting in higher electron mobility and saturated electron velocity, allowing these thin-film PV modules to absorb more energy from photons and deliver higher efficiency.
The major setback of GaAs and Ge thin-film solar cells is their high manufacturing cost and difficulty in growing for mass production. Even though this is a limitation, its high efficiency reaching up to 68.9% makes it uniquely suitable for space applications and concentrated photovoltaics (CPV).
Cadmium Telluride (CdTe) & Copper indium-(Gallium)-Selenide (CIGS and CIS): The most popular thin-film for commercial applications
Cadmium Telluride (CdTe), Copper Indium-Gallium Selenide (CIGS), and Copper Indium Selenide (CIS) comprise another important group of thin-film solar technologies. The record efficiency is set at 22.1% for CdTe, 22.2% for CIGS, and 23.5% for CIS. They also feature a highly competitive cost per watt ($/W).
Just like with other thin-film solar technologies, CdTe, CIGS, and CIS PV modules are manufactured by depositing thin layers of semiconductor materials using techniques like sputtering, evaporation, electrochemical deposition, and others. The backing material determines the flexibility of the module and therefore its application.
CdTe, CIGS, and CIS thin-film solar panels are not as popular as crystalline silicon for residential applications because of a lower efficiency and a larger space per watt required, but they are less expensive. The lower cost per watt makes these technologies uniquely qualified for solar power plants where installation space is not a limitation, but costs have to be brought down to a minimum.
The usage in commercial applications is the most important role that these thin-film solar technologies play in the PV industry. Technologies like CdTe, CIGS, and CIS are used to create electronic devices with embedded solar power generation, portable PV modules, BIPV, solar shingles, flexible PV modules for multiple applications, and more.
In the past, CdTe, CIGS, and CIS were not the only popular thin-film solar technologies used for commercial applications. Other important technologies that held a significant market share were Amorphous Silicon (a-Si) and Micromorph Silicon (μ-Si), but a failure to increase efficiency and reduce cost caused them to gradually disappear from the market.
Organic Thin-Film PV (OPV) & Perovskites: Other important thin-film technologies being developed
Thin-film solar panels have not reached their peak, since the scientific community is still working on researching and developing new and more advanced technologies. The current trend under research includes organic thin-film PV (OPV) and tandem cells with a perovskite base, both holding a promising future in the PV industry.
OPVs are made using two semiconductor materials sandwiched together, with one of the layers being a conductive dye or organic semiconductor. This technology shows a promising future by delivering a low production cost and high stability and it could cause a rapid shift in the PV market of the future if current limitations are overcome.
Tandem solar cells consist of a thin-film solar technology that stacks perovskite p-n junction layers on a base of crystalline silicon or other thin-film solar cells, showing a promising future for competing against traditional crystalline silicon due to its potential low cost and high efficiency. The record efficiency for tandem solar cells is currently set at 28.3% for c-Si-based cells, and at 26.2% for CIGS-based cells.
Challenges for tandem perovskite solar cells include water sensitivity, wide band gap, uncontrolled crystallization, and others. OPV cells also have to be developed as large-size solar cells and solve a few other setbacks to hit the market. In the future, these thin-film solar technologies could replace rigid and other thin-film PV modules, by providing higher flexibility, lower costs, and lower weight for PV modules.
Pros & cons of thin-film solar technology
Learning about the pros and cons for the different groups of thin-film solar technology is a great way to understand its unique features. In this section, we address each one of them.
Thin-film solar technologies like GaAs and Ge are able to deliver an astonishing performance, but for a higher cost. Other thin-film solar technologies like CdTe, CIGS, and CIS may require a large space to fit the same PV system that you would install with c-Si PV modules, but a better cost-efficiency and unique properties, make these technologies uniquely qualified for commercial applications.
As these technologies are further developed, future breakthroughs could increase their efficiency and reduce costs, making them more popular and increasing their market share. The following table illustrates the most important pros and cons for each group of thin-film solar technologies:
|GaAs & Ge||Higher efficiency of up to 68.9%||High manufacturing cost|
|Low operating temperature||Higher solar cell degradation|
|Power generation in low-light conditions||PV modules are more delicate|
|Small temperature coefficient|
|CdTe, CIGS, and CIS||Robust and resistant materials||High solar cell degradation|
|Small temperature coefficient||Lower efficiency than c-Si|
|Higher savings in large-scale installations|
|Ideal for unique commercial applications|
|Possibility to produce flexible modules|
|OPV & Tandem Perovskite||Potential to deliver higher efficiency than crystalline silicon||Most still in the research & development stage|
|Low production cost||OPV still has to be produced in large-size solar cells|
|Tandem perovskite has to overcome several setbacks|
GaAs and Ge are among the best and most efficient thin-film solar technologies. These thin-film solar panels provide great efficiency and perform great in low and high-temperature climates, being uniquely suited for CPV and space applications. The major cons of these technologies are a high manufacturing cost and higher than normal solar cell degradation.
CdTe, CIGS, and CIS thin-film solar technologies have proved their worth in the PV industry. While less efficient than crystalline silicon, they have a better cost-efficiency ratio and are better for solar power plants. Their unique properties and low cost also make them ideal options for commercial applications like portable PV modules, BIPV, flexible solar panels, and others.
Tandem solar cells based in perovskite and OPV also have many advantages and great potential to impact the PV industry. The only inconvenience is that researchers have to find solutions to a few setbacks before these technologies can fully hit the market and be used for all types of commercial applications.
Thin-film solar panel market
The PV industry is mostly ruled by monocrystalline and polycrystalline silicon technology with a production share of around 95%. Thin-film solar technology is also a player in the PV industry, featuring a production share of 5% for usage in solar power plants, BIPV, space applications, regular rooftop PV installations, and more.
In 2021, the thin-film solar market was valued at $12.2 billion, and $14.7 billion dollars by 2022, or about 5% of the whole PV market. Additionally, in 3 years from 2018 to 2021, the gross world production (GWp) for CdTe thin-film solar grew threefold, becoming the most popular thin-film solar technology produced worldwide.
The most important applications of thin-film solar technology
Thin-film solar panels include several technologies with different characteristics and properties. In this section, we explain important applications for thin-film solar technologies like GaAs, Ge, CdTe, CIGS and CIS.
Building Integrated Photovoltaics (BIPV)
Building Integrated Photovoltaics (BIPV) can be used for façade, rooftops and glazing. This application replaces the rooftop, windows (glazing), and façade of any building with aesthetically superior thin-film solar PV modules that fully integrate into the design of the building, providing it with the capacity to generate solar power for on-site use or to be exported to the grid.
The return on investment (ROI) for BIPV can be roughly estimated from 10 to 15 years, depending on the specifics of the system and location. BIPV systems can last for up to 30 years, supplying most or all of the power required to run a building. Popular technologies used for BIPV include CdTe, CIGS and CIS.
Concentrated photovoltaic (CPV) applications
Low to high-concentrated Photovoltaics or CPV uses optical devices to concentrate sunlight into the surface of PV modules. CPV can be used with any solar panel, but high-efficiency thin-film solar panels like GaAs and Ge are better for these applications since a PV module can produce 30% to 40% more energy than in regular conditions.
Spacecraft like satellites, space stations and rockets are exposed to radiation and limited weight can be carried out into space, making highly efficient and lightweight thin-film PV modules like GaAs and Ge, uniquely suited for these applications. While they are expensive technologies, it is more cost-efficient than carrying heavier-weight modules into space.
Thin-film solar technology like CdTe, CIGS and CIS features robustness, flexibility, low cost, and high efficiency making them better for portable applications. Some of these include foldable thin-film solar panels, solar phone chargers, solar flashlights, devices in general with embedded solar cells, and more. Future portable applications might include solar smartphones.
Public devices/equipment applications
Government and local authorities also take advantage of thin-film solar technology to install devices and equipment for public applications, making them independent from the grid and reducing their power consumption cost. Some of these applications include public Wi-Fi routers with solar panels, traffic lights operating with thin-film solar modules, solar street lights, and more.
Boats, RVs, buses and other vehicles also take advantage of solar energy thanks to thin-film solar technology. Some drivers carry portable thin-film solar panels in their vehicles, while others take it even further by installing flexible modules over the bow of boats, hoods or roofs of RVs, and more.
Rooftop PV installations
Thin-film PV installations are not as popular as c-Si ones, but they still happen. Some applications include thin-film technology based solar shingle installations and PV installation over business buildings, but mostly thin-film solar farms in utility-scale and industrial installations, where lower cost is important and space is not a limitation.
Final Word: Future and limitations of thin-film PV technology
Understanding the limitations and expected future of thin-film solar technology can be helpful in determining how this branch of the PV industry will develop. For instance, a-Si thin-film solar technology did not overcome efficiency and cost setbacks, making it shift out from the PV market in previous years. There are also concerns about toxic materials and scarcity of materials regarding thin-film solar products.
Surprisingly enough, there is also interesting news for thin-film solar technologies.
An important one is that certain thin-film solar technologies like GaAs may have future applications that go beyond the ground of solar power generation and step on the terrain of power transfer with the use of optics. Additionally, thin-film solar technologies using new materials might be developed in the future.
It has been estimated that the thin-film solar technology industry will grow by around 10% by 2030. With breakthroughs, the future may shine even brighter on thin-film solar technology, as it is further developed and takes on a higher market share in the PV industry.