An innovation from the University of Toronto, Canada, could facilitate printing low-cost perovskite solar cells.

These cells depend on a layer of tiny crystals made of low-cost, light-sensitive materials. The raw materials can be mixed into a liquid to form a kind of ‘solar ink’, which could be printed onto glass, plastic, or other materials using a simple inkjet process.

A low-temperature process removes a key barrier to the manufacture of low-cost perovskite solar cells. Photo: Kevin Soobrian/University of TorontoBut to generate power, electrons excited by solar energy must be extracted from the crystals so they can flow through a circuit. That extraction occurs in the electron-selective layer (ESL), and the difficulty of manufacturing a good ESL has been a barrier to perovskite solar cell development. Baking at high temperatures, the accepted process for ESL realization would melt plastic and other likely substrates.

A remedy devised by the researchers uses a new chemical reaction that supports the growth of an ESL made of nanoparticles in solution. The layer is produced directly on top of the electrode, and while heat is still needed, temperatures are kept blow 150 C.

A coating of chlorine atoms, which helps the nanoparticles bind to the perovskite layer on top and allows for efficient extraction of electrons. A 20.1% efficiency was measured for the resulting solar cells, just slightly below the 22.1% documented for perovskite cells manufactured with the older, high-temperature method.

Many perovskite solar cells experience a severe drop in performance after only a few hours, but the new cells retained more than 90% of their efficiency even after 500 hours of use.