Most solar cells today are silicon-based, either monocrystalline (most expensive, highest reported efficiency) or amorphous (less expensive, somewhat less efficient). Perovskites are a class of material which are (quoting Wikipedia), “...any material with the same type of crystal structure as calcium titanium oxide (CaTiO3), known as the perovskite structure... the general chemical formula for perovskite compounds is ABX3, where 'A' and 'B' are two cations of very different sizes, and X is an anion that bonds to both.”. Conversion efficiencies with PV cells built with these materials have historically been low (sub-10% as opposed to the 20+% of silicon) but they offer they offer the potential of very much lower manufacturing costs as they can be produced with solution chemistry (coating and /or printing).
imec, and its partners in the Solliance collaboration (see below) now report achieving power conversion efficiencies of up to 12%. imec regards this as particularly encouraging as it has been working on the technology for only a short time, around two years; the researchers say they have been able to apply many of the lessons learned over many years of refining silicon cell technology to deliver rapid advances in the performance of perovskite cells, and anticipate that the trajectory they have established will yield still higher efficiency in the near future.
By depositing thin active layers, and refining the cell patterning and interconnection (again drawing on its silicon experience) imec reports being able to produce semi-transparent and efficient cells. Cells need electrical connections from the front (top surface) of the structure to the substrate, but also need the maximum ratio of active to total area.
Transparency takes the technology in two directions; it enables semi-transparent PV-windows which are a key towards Zero-Energy Buildings (in compliance with EU and other directives) and building integration. However, the perovskite cells capture and convert a different range of wavelengths to silicon. By stacking a semi-transparent cell over a conventional silicon cell, both can contribute and imec believes overall efficiencies of over 30% are within reach.