With PV power having gained ever larger shares on the power markets of various countries, a major factor for its further development is all-out exploration of perovskite, a key material which can boost the performance and cut the cost of PV power, according to researchers.
Perovskite cell has gained growing attention on the PV market, thanks to the rapid increase of its conversion rate, to 22% now, since its debut in 2009, approaching 25% of silicon cell, which has stagnated at the level for a long time.
So far, perovskite cell has outperformed all other PV cells with new materials, such as DSSC and organic PV cell.
DSCC, a low-cost thin-film PV cell, for instance, is an electricity-chemical system, featuring semiconductor consisting of light-sensitive electrode and electrolyte, which is very cheap, with cost of its process even lower than that of transistor cell. It can be made in the form of film, needing no protection. Although its energy-conversion rate is still lower than that of best thin-film cell, its performance/price ratio is sufficiently high.
Perovskite is an oxide mineral, featuring a three-dimensional crystal structure, with chemical formula of ABX3, in which A and B are two cations in different sizes and X an anion (often oxygen), for combination with the former two.
▲ Diagram of perovskite crystal (source: Cadmium at English Wikipedia)
Scientists have substituted other elements for calcium, titanium, and oxygen in the material, thereby improving its chemical properties and make it more suitable for PV application. A noticeable compound is（CH3NH3）PbI3.
A number of blockades have to be overcome for the commercialization of perovskite, though, mainly development of sealing technology to insulate water, as perovskite crystal tends to dissolve in humidity; maintenance of high efficiency in large-sized perovskite cell, which is now confined to only small cell (about the size of a nail).
At present, perovskite cell is still no rival to silicon cell, given the latter's economy of scale. Financial Times reported that Michael McGehee, professor of materials science at Stanford University, has proposed covering silicon with perovskite for use in PV cell, with the former capturing wavelength in visible spectrum, while leaving others to silicon in the lower layer. Efficiency of such hybrid cell is 10% higher than that of silicon cell, according to the study of McGehee.
Perovskite PV cell can greatly boost the economic value of PV power, so long as the problems of stability and size can be overcome. In addition to low cost, perovskite crystals can be produced at temperature much lower than that of silicon.
(Collaborative media: TechNews, first photo courtesy of Pixabay)
