Table of Contents
Introduction
Solar photovoltaic, or PV, technology converts sunlight directly into electricity using semiconductor materials. Although all PV systems are based on the same basic photovoltaic effect, there are several distinct types of PV technologies that differ in materials, structure, appearance, performance, and typical applications. Understanding these main families helps to make sense of why solar panels look different, have different efficiencies, and are used in different ways.
Main Families Of PV Technologies
The most important way to classify solar PV technologies is by the type of semiconductor material and how it is manufactured. At a high level, three families dominate the market today: crystalline silicon, thin‑film, and emerging or next‑generation technologies such as perovskites.
Each family has its own strengths and weaknesses in terms of efficiency, cost, flexibility, and visual appearance. These differences influence where each type is used, from rooftop systems to building facades or large solar farms.
Crystalline Silicon PV
Crystalline silicon, often abbreviated c‑Si, is the most widely used PV technology. It uses wafers of purified silicon similar to those used in the electronics industry. The wafers are assembled into cells, which are then connected and laminated into modules, commonly called solar panels.
Crystalline silicon technologies are generally divided into monocrystalline and multicrystalline, also called polycrystalline. Both use silicon crystals, but their crystal structure and manufacturing process are different, which affects their color, efficiency, and how they are used.
Monocrystalline Silicon
Monocrystalline silicon cells are cut from a single, continuous silicon crystal. Because the atoms are arranged in a very regular and uniform structure, electrons can move more easily when light is absorbed. This typically leads to higher efficiencies compared with other silicon types.
Monocrystalline panels usually have a darker, almost black appearance and often feature cells with rounded corners. They tend to achieve some of the highest commercial module efficiencies among mature technologies. This means that for the same panel size, a monocrystalline panel can produce more power than a less efficient technology.
The main implication of higher efficiency is that monocrystalline panels are very useful where space is limited, such as on rooftops with small areas or on applications where power density is important. Historically, they were more expensive, but improvements in manufacturing have significantly reduced costs, so they are now commonly used in many residential and commercial projects.
Multicrystalline (Polycrystalline) Silicon
Multicrystalline or polycrystalline silicon cells are made from blocks of silicon that contain many small crystals rather than a single uniform crystal. When the silicon solidifies, grains form with boundaries between them. These grain boundaries can slightly hinder electron movement, which tends to reduce efficiency compared with monocrystalline cells.
Polycrystalline panels usually have a blue or speckled appearance. They once had a clear cost advantage, because it was simpler and cheaper to make large blocks of multi‑crystal silicon than to grow single crystals. However, differences in cost have narrowed over time as manufacturing for both types has improved.
Because of their slightly lower efficiency, polycrystalline panels need a little more area to produce the same power as monocrystalline panels. They have been widely used in large ground‑mounted solar farms where land is relatively available and the slightly lower efficiency is less critical. In some markets their share is declining in favor of high‑efficiency monocrystalline products.
Passivated Emitter And Back Contact And Other High‑Efficiency Variants
Within crystalline silicon there are more advanced cell designs that improve efficiency beyond traditional cells. One prominent example is passivated emitter and rear cell, often abbreviated PERC. These cells use a special layer on the back of the cell to reduce electron recombination and to reflect some light back into the cell, which improves overall performance.
There are also other high‑efficiency concepts such as heterojunction cells, which combine crystalline silicon with thin amorphous silicon layers, and back‑contact cells, which place all electrical contacts on the rear so the front surface can capture more light. These designs raise the practical efficiency of silicon modules and are becoming more common in premium products.
Thin‑Film PV Technologies
Thin‑film PV technologies use very thin layers of semiconductor materials deposited onto a substrate such as glass, metal, or flexible plastic. The semiconductor layer can be thousands of times thinner than a silicon wafer. This makes thin‑film modules lighter and sometimes flexible, and it can allow different shapes or colors.
Thin‑film modules generally have lower efficiency than crystalline silicon modules, which means they require more area to produce the same amount of power. However, they can be advantageous in certain niches, such as building‑integrated applications, large utility‑scale plants where land is abundant, or lightweight systems where mounting heavy glass modules is difficult.
The main commercial thin‑film technologies are amorphous silicon, cadmium telluride, and copper indium gallium diselenide.
Amorphous Silicon (a‑Si)
Amorphous silicon, abbreviated a‑Si, uses silicon atoms arranged without a regular long‑range crystal order. This disordered structure is deposited in very thin layers on a substrate. Because of its different structure, amorphous silicon absorbs light more strongly per unit thickness than crystalline silicon, so very thin layers can be sufficient.
Amorphous silicon cells have lower efficiency than crystalline silicon cells, so they are less common in large power‑producing modules today. Historically they were often used in small consumer devices such as calculators, watches, or small solar gadgets, where low power and flexible shapes were more important than maximum efficiency.
On building surfaces, amorphous silicon can be produced as semi‑transparent or colored glazing panels, which support architectural applications where the aesthetics matter as much as energy yield. However, many of these applications are now also served by other thin‑film or advanced crystalline products.
Cadmium Telluride (CdTe)
Cadmium telluride, or CdTe, is a thin‑film material with strong light absorption and relatively simple manufacturing. CdTe modules usually have a uniform dark appearance. They can be manufactured on large sheets of glass in a continuous process, which helps to keep production costs low.
CdTe modules generally have lower module efficiencies than the most advanced monocrystalline silicon panels, but they can be competitive in cost per watt, especially in large utility‑scale solar farms. They are often used in very large ground‑mounted installations.
A specific feature of CdTe technology is the use of cadmium, a toxic heavy metal. In commercial modules the cadmium is locked in a stable compound and laminated between glass layers, which keeps it contained during normal operation. At the end of the module’s life, proper recycling is important to avoid environmental release and to recover valuable materials. This environmental aspect is one reason why robust collection and recycling programs are emphasized for this technology.
Copper Indium Gallium Diselenide (CIGS)
Copper indium gallium diselenide, commonly abbreviated CIGS, is another thin‑film technology that uses a mixture of metals and selenium as the absorber. It has very high light absorption and can reach cell efficiencies comparable to or higher than some crystalline silicon cells in the laboratory.
CIGS modules can be produced on rigid glass or on flexible substrates such as metal foils or polymers. Flexible CIGS modules can be lightweight and bendable, which allows applications on curved surfaces, lightweight roofs, and portable systems. The visual appearance is typically uniform and dark, which architects may find attractive.
Commercial CIGS production has been more limited and has faced strong competition from falling crystalline silicon prices. As a result, CIGS is present in specific niches, such as specialty building‑integrated products or lightweight modules, rather than dominating mainstream markets.
Emerging And Next‑Generation PV Technologies
Beyond crystalline silicon and established thin‑films, several new PV technologies are under development. These aim to reduce costs further, improve efficiency, or offer new properties such as transparency or color. While many are still in research or early commercial stages, they are important for the future of solar energy.
Perovskite Solar Cells
Perovskite solar cells use materials with a specific crystal structure known as the perovskite structure. These materials can be made from inexpensive precursors and processed at relatively low temperatures, for example by printing or coating methods. Perovskites have shown very rapid improvements in efficiency in the laboratory, reaching levels comparable to high‑end silicon cells in only a few years of development.
One attractive idea is to combine perovskite cells with silicon cells in a tandem structure. In a tandem, one cell absorbs high‑energy (short wavelength) light while the other absorbs lower‑energy (longer wavelength) light. By dividing the solar spectrum between two layers more efficiently, the combined device can surpass the efficiency of either cell alone.
Perovskite technology still faces challenges with long‑term stability outdoors and with the use of certain materials that may be toxic if not properly contained and recycled. Researchers and companies are working to solve these issues and to move from laboratory cells to durable, mass‑produced modules. If these challenges are overcome, perovskites could significantly change the cost and performance landscape of PV.
Organic PV And Dye‑Sensitized Solar Cells
Organic photovoltaic cells use carbon‑based molecules or polymers that can conduct electricity when light is absorbed. They can be made into very thin, lightweight, and sometimes semi‑transparent films. Their main advantages are potential low cost, flexibility, and the ease of printing on large areas.
Dye‑sensitized solar cells use a dye molecule to absorb light, with electrons transferred into a semiconductor layer. These cells can be made semi‑transparent and in different colors, which is attractive for building integration, glass facades, or even consumer products where visual design is important.
These technologies generally have lower efficiencies and shorter lifetimes compared with crystalline silicon at present, which limits their use in applications that require high, long‑term power output. However, they remain interesting for special uses where aesthetics, flexibility, or low weight are more valuable than maximum efficiency.
Specialized And Application‑Specific PV Forms
Beyond the basic materials, PV technologies can also be distinguished by how the cells are assembled into products that suit particular uses. These forms can involve any of the underlying materials described above, but they are shaped or integrated differently for specific functions.
Bifacial Panels
Bifacial PV modules are designed so that both the front and the back of the panel can absorb light and generate electricity. The front side receives direct sunlight as usual, while the backside captures light reflected from the ground or other surfaces and scattered light from the sky.
Many bifacial modules are based on monocrystalline silicon with glass on both sides of the panel. When installed above bright or reflective surfaces and with enough space between the module and the ground, bifacial modules can generate more energy per installed capacity than conventional one‑sided modules.
The gain from bifacial operation depends strongly on the installation environment. For example, installing them over white or light colored surfaces typically provides more reflected light than over dark soil. Because of this, bifacial modules are particularly attractive in large solar farms, rooftops with bright coverings, or over water and light pavements.
Flexible And Lightweight Modules
Some PV technologies can be manufactured on flexible substrates, which leads to thin, bendable solar laminates. Flexible modules are often based on thin‑film materials such as CIGS or amorphous silicon, but new flexible crystalline silicon products have also appeared, using very thin cells and special encapsulation.
Flexible modules are especially useful where weight and curvature matter. Examples include weak roofs that cannot support heavy glass modules, curved surfaces such as some industrial roofs or vehicle roofs, and portable systems such as foldable solar chargers. There is usually a trade‑off between flexibility and maximum efficiency, but for these uses flexibility is often more important.
Building‑Integrated Photovoltaics (BIPV)
Building‑integrated photovoltaics refer to PV materials that are part of the building envelope itself, such as roofs, facades, skylights, and shading elements. In BIPV products, PV replaces conventional building materials rather than being added on top.
Different PV technologies are suited to BIPV: crystalline silicon in the form of solar tiles or facade panels, thin‑film glass laminates such as CdTe or amorphous silicon, or even semi‑transparent and colored modules based on emerging technologies. The choice depends on visual appearance, weight, transparency, and local building requirements.
BIPV can help architects and developers combine energy production with aesthetics and functional building elements. It often requires careful design coordination between PV specialists and building designers, because the PV must meet both electrical and architectural standards.
Concentrator PV (CPV)
Concentrator PV, or CPV, uses optical elements such as lenses or mirrors to concentrate sunlight onto very small, high efficiency solar cells. By increasing the intensity of light on each cell, CPV can reach very high efficiencies per unit of cell area. Multi‑junction cells are commonly used in CPV, where different semiconductor layers each absorb part of the solar spectrum.
CPV systems require precise tracking of the sun so that the concentrated light stays aligned with the cells. They work best in locations with high direct sunlight and low cloud cover, since clouds scatter light and reduce the effectiveness of concentration. Although CPV is not a large share of the overall PV market, it illustrates how PV technologies can be adapted when very high performance is needed and conditions are suitable.
Comparing PV Technologies In Practice
In practical terms, the choice between different PV technologies depends on several factors. Crystalline silicon, both monocrystalline and polycrystalline, dominates the global market due to its combination of high efficiency, declining cost, and long‑term field experience.
Thin‑film technologies are selected when specific advantages matter, such as uniform appearance, performance in high temperatures or diffuse light, or lower cost in very large installations with ample space. They can also be useful where lightweight or flexible modules are important.
Emerging technologies, such as perovskites, organic PV, and dye‑sensitized cells, are not yet common in main power markets, but they open possibilities for new kinds of solar products. These may include colored and transparent surfaces, very light and flexible films, or highly efficient tandem combinations with silicon.
To compare performance, PV engineers often refer to module efficiency, which is the ratio of electrical power output to the solar power incident on the module area. If a panel produces electrical power $P_{\text{out}}$ from an area $A$ under sunlight with power density $G$ (irradiance), the efficiency $\eta$ is:
$$\eta = \frac{P_{\text{out}}}{G \cdot A}$$
The module efficiency $\eta$ is defined as:
$$\eta = \frac{P_{\text{out}}}{G \cdot A}$$
where $P_{\text{out}}$ is the module’s electrical output power, $G$ is the solar irradiance, and $A$ is the module area.
Different PV technologies have characteristic efficiency ranges, which influence how much area is needed for a given power output. A higher efficiency technology can deliver more power from the same rooftop or land area, while a lower efficiency technology might still be attractive if it offers lower cost, better aesthetics, or special features.
Conclusion
Types of solar PV technologies can be grouped into crystalline silicon, thin‑film, and emerging next‑generation families. Within each group, specific materials and designs offer combinations of efficiency, cost, flexibility, and appearance that suit different applications, from high power rooftop systems to integrated building elements and portable devices. As research and manufacturing progress, the balance between these technologies may shift, with new options becoming available for both large and small solar energy systems.