Thin-film solar cells use less material, resulting in a significantly lower cost per module compared to stacked solar cells. Their manufacturing process also requires less energy. Furthermore, they feature integrated interconnect modules, eliminating the costs associated with fixing and internally connecting individual modules. Thin-film solar cells represent a novel photovoltaic device for alleviating the energy crisis.
Types of thin-film solar cells
Currently, thin-film solar cells aim to achieve two goals: first, to possess sufficient flexibility to adhere to the surfaces of large building materials; and second, to achieve the same efficiency as, or even higher than, traditional solar cells. Different fabrication techniques result in thin-film solar panels with varying advantages and disadvantages compared to traditional solar panels. The naming of thin-film solar panels is usually derived from the type of semiconductor material used.
1. Amorphous silicon (a-Si)
Amorphous silicon was the earliest and most mature material used to make thin-film solar cells. This is likely because crystalline silicon has long been used in traditional solar cells, and people have a thorough understanding of the properties of silicon electrons.
Advantages: Unlike crystalline silicon, amorphous silicon has a higher solar energy absorption rate, making it possible to fabricate thin-film structures and effectively reducing costs. Due to its abundant, non-toxic, and inexpensive raw materials, amorphous silicon has rapidly become the primary method for thin-film fabrication and is entering the mainstream.
Disadvantages: Due to its low conversion efficiency, it is mostly used only in small-scale, flexible electronic products.
2. Cadmium telluride (CdTe)
CdTe-based solar cells are the second most popular photovoltaic technology, with a stable conversion efficiency of around 5%. Their manufacturing process is simple and rapid, comparable to silicon-based materials. This improved conversion efficiency has further promoted their application.
Advantages: CdTe is cheaper than silicon-based solar cells, and more importantly, it has minimal carbon emissions and a short payback period. Although CdTe, along with other thin-film materials, still lags behind traditional c-Si panels in efficiency, the gap is narrowing. In 2015, a company called First Solar achieved a CdTe solar panel with an average commercial efficiency of 16.1%.
Disadvantages: A major drawback of CdTe is that it requires "extraordinary" materials to manufacture. Cadmium is a highly toxic substance that can accumulate in the food chain like mercury, which contradicts the principles of environmental friendliness, safety, and non-toxicity. Many institutions and laboratories are searching for environmentally friendly and highly efficient alternatives, and solar energy manufacturers are exploring methods for recycling and reusing cadmium-containing materials to address environmental issues.
3. Copper indium gallium selenide (CIGS)
This type of solar cell is another popular semiconductor type. The technology for fabricating CIGS is gaining increasing attention in Europe and Japan, and manufacturers worldwide are using it to fully realize the conversion efficiency potential of environmentally friendly materials.
Advantages: CIGS is an environmentally friendly material, which benefits manufacturers seeking long-term profits. Solar cells made from CIGS have higher potential efficiency and greater thermal resistance compared to other thin-film materials. Due to its resistance to decomposition, it has great potential for application in devices with long lifespan requirements.
Disadvantages: CIGS technology has not yet surpassed traditional silicon-based solar panels, although its conversion efficiency has improved significantly in recent years. While laboratory-synthesized efficiencies exceed 20%, practical applications show efficiency less than half of the experimental values.
4. New Copper-Zinc-Tin-Sulfur Method (CZTS)
In the search for solar cell materials that are both environmentally friendly and abundant in raw materials, CZTS was discovered by scientists. CZTS is similar to CIGS in terms of performance and preparation methods, but its efficiency is lower.
Advantages: CZTS is composed of copper, zinc, tin, and sulfose selenides, which are abundant on Earth. This means that the compound is both environmentally friendly and inexpensive. However, tellurium and indium, found in CdTe and CIGS, are scarce on Earth.
Disadvantages: CZTS is still in the early stages of development. To achieve commercialization, high efficiency requirements have been set, and the current achievable conversion efficiency is around 7.6%. Only when the efficiency reaches at least 20% can it become a leader among similar solar cells.
