In recent decades there has been an explosion of innovation in the solar energy field. This innovation has moved in two directions: the exploration of new materials that may provide greater efficiency and power, and the refinement of currently used materials to be more efficient and to lower cost of production.
As with all technological innovations, the newest, most powerful, and “best” solar energy materials are the most expensive and most challenging to manufacture. However, we can expect that these two paths of innovation will continue to make solar energy more available at a lower cost in the coming years.
Currently, we have several different types of photovoltaic materials, and each could be considered the best in a specific instance or application.
Nearly 90% of the world's solar panels use some variation of silicon, as it is an incredibly efficient photovoltaic material. Nearly 95% of all solar panels made in the US for residential use are made of crystalline silicon. Crystalline silicon is an excellent substance to transmit solar energy because the cells align in a crystal structure; the more perfect the structure, the more efficient it is at transmitting energy.
Various substances and processes are used to enhance the purity of the crystal structure and reduce inefficiencies, but they can also drive up costs. To reduce light reflection, and therefore increase efficiency, crystalline silicon is also often coated with additional materials to absorb light. Crystalline silicon yields an energy efficiency of up to 22%, higher than any other widely available material, and can last for up to 25 years without degradation.
In almost all consumer applications, there are two types of crystalline silicon solar panels:
Monocrystalline Silicon Solar Cells
These cells are made of high-purity silicon, produced in ingots and then cut into wafers. They have an even coloring and uniform look, due to the high purity of the crystalline structure. Due to their purity, they have the highest efficiency of any consumer-level solar panel material. They last the longest, and perform better in low-light and warm weather conditions. Because they are so efficient, they can generate more power in a smaller space than other types of solar panels.
However, they are also the most expensive for the consumer, and expensive in production. Because monocrystalline silicon is produced in a cylindrical shape that is then trimmed square, a lot of the product is lost as waste. There is also a risk that the entire panel will break down if partially covered by snow, dirt, or shade.
Polycrystalline Silicon Solar Cells
Polycrystalline silicon solar cells are easier to manufacture than monocrystalline, because they are simply made by pouring raw silicon into a square mold. This process creates a less perfect crystalline structure, reducing the efficiency of the solar cells, but improves efficiency in manufacture, which lowers cost to the consumer. Polycrystalline silicon solar cells have an efficiency of just 13-16%, unlike the 15-20% of monocrystalline cells. For this reason, they take up more space in a typical installation. They are also more susceptible to high-heat conditions, and don't last quite as long.
Thin Film Solar Cells - Amorphous
Thin film solar cells can be made of a variety of substances, but are most commonly made of amorphous silicon. Amorphous silicon does not have the crystalline structure, so it is only capable of efficiencies around 7%. However, thin film solar cells have some special advantages in certain applications. These solar cells are lightweight and flexible, the kind typically used to power calculators. They are inexpensive to make, and highly resilient to shade or high temperatures.
More excitingly, thin-film solar cells are flexible, which opens up new avenues for innovation and exploration. For example, people are using thin film technology to make portable tarps for camping that can also generate solar energy. However, due to the reduced efficiency, thin-film solar cells usually need to be quite large in order to deliver significant energy.
We have yet to find a way to minimize the footprint of these solar cells. They are also not as durable as crystalline silicon solar cells. As we look into new applications for flexible, wearable technologies, thin-film solar cells provide new ways to power lightweight, portable, flexible devices, and we can expect that the efficiency will be improved.
Gallium arsenide is a photovoltaic material that has generated a lot of excitement in recent years. It is incredibly efficient, and has a very high energy yield in a small amount of space, with efficiency starting at 10-12%, with a smaller band gap than silicon. However, gallium is more rare than gold, and is an expensive material, and arsenic is a poisonous substance that creates hazards during the manufacturing process. While gallium arsenide is a substance that is an excellent transmitter of solar energy, it may not be a material that we ever see in widespread residential use.
There are even more photovoltaic materials in existence, and researchers are studying them for commercial use and innovation, even as we continue to refine production of the various silicon panels in use today. As you can see, because of the various manufacturing processes and efficiency considerations, there is no single “best” photovoltaic substance; each has its advantages and disadvantages depending on use case, climate, durability, cost of production and installation, and other factors. If you are choosing the best material for solar panel installation on your home, the primary factors to consider would be the amount of space you have, and your budget for the project.
For many homeowners, the additional cost of monocrystalline silicon solar cells proves to be a good investment, because the cost is offset by the space efficiency, energy efficiency, and durability of the cells. However, in milder climates where space is not an issue, monocrystalline silicon may not be worth the investment, and it would make more sense to go with polycrystalline silicon. Consider your needs before determining which substance is the best transmitter of solar energy for your home.