Solar cells are devices which convert light energy into electrical energy. In order to work properly, the cells must be covered with a semiconductor material that can absorb the light. Silicon solar cells are solar cells which are coated with silicon, and are the most common type used. These cells are connected in series called modules, and the modules are interconnected to form an array that produces the desired voltage. These are then placed into a protective container behind panels of glass which direct the sunlight to the cells.
When light hits the solar panel, the photons are absorbed by the semiconductor material. The electrons are knocked loose and flow through the material producing electricity. An array of silicon solar cells converts this energy to direct current (DC) electricity. In an integrated system, the electricity is then fed into the electricity grid using inverters. Stand-alone solar products store the electricity in batteries.
While silicon is a very common element, it is usually bound in silica. The pure silicon must be extracted from the silica, and then processed to increase its conductivity. Pure silicon is a poor conductor of electricity, but when certain impurities are added, typically phosphorous atoms, it becomes an excellent conductor. This processing expends a great deal of energy, and is responsible for the high cost of silicon solar cells. Traditionally manufactured cells use single-crystal silicon in a bulk form which is cut into wafers.
To help mitigate the cost, scientists have developed thin film silicon solar cells. These use only about one percent of the silicon a traditional cell would use, but unfortunately, they are much less efficient. Cells made with multiple layers of thin film have been developed which are as efficient as the more expensive traditional cells, and yet maintain the benefits of lower cost, lighter weight and greater flexibility. Polycrystalline and amorphous thin film silicon cells are additional, lower-cost options.
Another challenge for scientists is to find a way to increase the effectiveness of silicon solar cells. Sunlight has a wide range of wavelengths containing photons with a wide range of energies. Some of these are too weak or too strong to form the electron-hole pair required to be captured by the semiconductor material. Most cells are only 15% efficient, which means they only capture 15% of the electrical energy available in the sunlight which passes through the panels.
Work is being done world-wide to find ways to increase the efficiency and decrease the cost of silicon solar cells. Finding ways to increase thin-film efficiency, thereby greatly decreasing the cost, is a priority of a European Union-funded research project. A company in Japan has developed silicon solar cells for use in multiple products which has an average efficiency of 25%. Boeing-Spectrolab, a US corporation has developed a concentrator silicon solar cell that has 40.7% efficiency.
Mare research and development is required before solar power becomes a primary energy source, yet this is an area that is receiving international attention and funding. As cost decreases and efficiency improves, solar energy may become much more commonplace. Even with these challenges, silicon solar cells are already used in a variety of products. These include every day items such as calculators, flashlights, phone chargers, water fountains, and domestic and commercial hot water systems.