ALD coatings for next-generation solar cells

Researchers at the University of Helsinki are developing thin films needed in new types of halide perovskite solar cells, and matching ALD processes, in order to provide increasingly affordable solar cells, enable their integration into objects and, consequently, promote the transition to renewable energy.

Most commercial solar cells are silicon-based, and apply PERC Passivated Emitter and Rear Cell) technology originally launched in 1983 by Martin Green, a recently awarded Millennium Award. However, increasingly efficient, inexpensive and durable solar cells are being developed all over the world. Even in the case of silicon-based cells, a transition is underway to novel techniques, including the tunnel oxide passivated contacts TOPCon) concept, where several layers of silicon and oxide are added to the cell.

In addition to silicon, other solar cell technologies are being investigated. The most promising new technique is based on the use of halide perovskites as a light absorbing material. The general chemical formula of halide perovskites is ABX3, where A is an alkali metal or an amine, B is tin or lead, and X is a halide. The most commonly studied compound is methylammonium lead iodide CH3 NH3 Pbl3. Perovskite solar cells are on the verge of commercialization, and some manufacturers believe they will be mainstream in a couple of decades.

“As these new types of solar cells can be transparent, they can be installed in, for example, windows. They are also flexible, which increases their uses,” says Senior University Lecturer Marianna Kemell, who heads the research project funded by the Academy of Finland.

Even though halide perovskite solar cells have achieved high efficiency levels, problems with cell stability and the lack of industrial-scale production techniques have constituted bottlenecks impeding their widespread adoption.