ilicon solar has made a huge leap in performance compared to early cell prototypes with a solar conversion efficiency of only 3%. Most silicon solar panels use the same crystalline silicon technology now as they did back then, but its radical improvement over more than a century added hugely to the efficiency. Today crystalline solar panels represent over 85% of the market and offer an efficiency of around 22%, meaning they can convert 22% of solar radiation that reaches their surface into electrical energy.
However, this well-established technology has its limitations, which spurred a search for alternatives. Solar thin film PV panels are among the few that were able to actually compete with crystalline silicon and sometimes even be more advantageous.
How are thin film solar cells different from traditional photovoltaics?
Like other PV modules, solar thin film PV panels convert sunlight into electricity using the photovoltaic effect. But unlike conventional modules, thin film panels harvest sunlight with one or more thin films, or thin layers of semiconducting material placed on glass, polymers, or metal foils. For a solar panel thin film structure means flexibility, lighter weight, and an easier manufacturing process. And even though the efficiency of solar thin film modules is lower than that of traditional solar panels, in some cases they may even be more cost-effective.
The 4 types of solar thin film cells
Amorphous silicon (a-Si)
Amorphous silicon is the oldest solar thin film tech. An a-Si solar thin film module is fabricated by depositing a layer of amorphous silicon onto a glass base using chemical vapor deposition (CVD). Due to a high absorption capacity, this PV thin film cell requires very little silicon – about a hundred times less than crystalline solar.
While a-Si thin film solar cells are easy and cheap to manufacture, their main weakness is their quicker degradation, even compared to other thin film panels. In addition to this, a-Si thin film modules tend to fail at low temperatures.
Copper indium gallium selenide (CIGS)
Copper indium gallium diselenide (CIGS), is the most efficient thin film solar technology. To create this solar panel thin film of semiconducting material made of copper, indium, gallium, and selenium is deposited on a plastic or glass substrate. A special three-stage co-evaporation technique provides a high absorption coefficient, enabling CIGS thin film solar cells to achieve a high conversion efficiency.
Cadmium telluride (CdTe)
Cadmium telluride solar modules are the most popular thin film panels and the second most popular PV technology on the market. CdTe thin film solar cells use thin film layers of cadmium telluride materials as a semiconductor – this uncomplicated structure simplifies and cheapens the manufacturing process.
Cadmium telluride thin film PV modules have some fairly significant drawbacks though. For example, CdTe thin film cells have encountered controversy due to their potential hazard, as cadmium is toxic and exposure to it is known to cause cancer. When used in conjunction with tellurium, however, cadmium forms a highly stable thin film material.
Gallium arsenide (GaAs)
Gallium arsenide is the ideal material for the production of thin film solar cells due to its exceptional light absorption and electrical properties. Moreover, the efficiency of GaAs thin film panels sometimes even surpasses the efficiency of crystalline silicon solar panels and reaches a 30% conversion rate. But unfortunately, gallium arsenide thin film cells use expensive components which makes GaAs thin film panels uneconomical despite their great performance.
Advantages of thin film solar
Thin film solar tech still has plenty of room for improvement, but it clearly provides a good set of benefits. Distinct price advantage is one of them: thin film cells use less semiconductor material which results in a lower end-user price. At the same time, thin film installations have a shorter payback period than traditional systems, in other words, consumers can break even on their investments faster.
Thin film manufacturing technique allows a thin film module to be shaped to fit even curved roofs and facades. What's more, thin film solar panels can absorb a broader range of wavelengths. Crystalline cells normally absorb only visible and near-infrared solar radiation, while some newer thin film alternatives capture more infrared and even partly ultraviolet light. This means thin film installations offer more working hours during the day and perform better in cloudy weather.
A solar panel thin film used in TF systems is lightweight and can be quickly rolled up. This means you can use thin film modules as portable heating devices and take them with you, for example, on camping trips. Plus, thin film systems are easier to install: thin film panels are more flexible and less prone to breakage due to the absence of rigid parts.
One more advantage of PV thin film systems over conventional installations is greater resistance of thin film cells to high temperatures. Solar panels are tested at 25° Celsius and tend to perform worse when the temperature exceeds that level, but a thin film module usually loses less efficiency compared to a crystalline one.
Disadvantages of thin film solar
Thin film systems come with some disadvantages, however. The primary problem with solar thin film PV panels is the efficiency of thin film cells. Even though some new prototypes perform even better than their crystalline counterparts, the majority of thin film systems still offer conversion levels between 13% and 19%.
In addition to this, a thin film module generally takes up more space for achieving the needed capacity than any crystalline pannel, which makes solar thin film options less suitable for residential applications. Thin film solar modules also have a shorter lifespan and warranty period as compared to other types of panels.
And finally, the environmental impact of PV thin film production still raises questions, primarily due to the use of cadmium in solar panel thin film manufacturing. However, cadmium-free non-toxic thin film solutions are becoming more common on the market.