By Dr. Peter Harrop, Chairman, IDTechEx
Perovskite photovoltaics efficiency gains are double those of organic PV, exciting researchers from KIMM in Korea to Dyesol in Australia. However, it is like the little girl, “When she was good she was very, very good and when she was bad she was awful”. Perovoskite photovoltaics promises over 20% efficiency, low cost materials and even flexible, transparent and stretchable versions dearly needed for new applications. Record power to weight ratio is needed for the electric vehicle end game, the land vehicles, boats and aircraft described in the IDTechEx report, “Energy Independent Vehicles 2016-2026”.
Ultrathin, flexible, stretchable and lightweight versions have been produced by Johannes Kepler University in Austria powering a miniature aircraft and airship. With 100% yield, exhibiting 12% efficiency they are only 3μm thick and weigh 5.2g m-3. Organolead halide perovskites are promising because they absorb light more efficiently: thinner layers are needed. Researchers suggest it could power EIVs as robotic insects and drones, and its flexibility and stretchability could be useful in bio-electronics.
But when she was bad she was awful. PbI, one of the breakdown products of the perovskite, is both toxic and carcinogenic. A glass panel can be made hermetically sealed, but plastics can be easily pierced. We need a barrier layer to make flexible versions last for 5-10 years, and yet still not be that much heavier and even then it will not be chewable by children as required for packaging and toys. OPV will be better for that.
The new IDTechEx report, “The Rise of Perovskite Solar Cells 2015-2025” finds that the stability of perovskite cells under ambient conditions is a persistent problem. The perovskite decomposes in the presence of water and the decay products attack metal electrodes. Heavy encapsulation to protect perovskite can add to the cell cost and weight. Water vapor penetrating the perovskite can produce reactive iodides that rapidly corrode the metal electrodes.
Progress is being made. New perovskite solar cells with 16% efficiency have been developed by researchers from Switzerland and China. Stable and moisture resistant, they overcome some of the problems of perovskites. An interlayer protects the metal, allowing the cells to preserve their efficiency for two days. The resulting solar cell has greatly enhanced stability because of stabilizing crosslinks in the material. These are formed by the phosphonic acid ammonium additive hooking together the perovskite crystallites through strong hydrogen bonding with the phosphorus and nitrogen-containing terminal groups of the linker molecule. The team explains that the additive allows the perovskite to be incorporated uniformly within and on the surface of a mesoporous titanium dioxide scaffold material. This nearly doubles the efficiency from 8.8 to 16.7% and it makes it moisture resistant, as the cations passivate the surface and render it inaccessible to water molecules. Next, the hysteresis in the J-V curves will be removed enhancing efficiency.
On the other hand, IDTechEx advises that lead free perovskites in photovoltaics have very low efficiency but the many other benefits may find them a market slot and they will be improved in efficiency in due course. All this will be covered by IMEC of Belgium, IDTechEx and others in presentations and masterclasses at the IDTechEx Show November 18-19 in Santa Clara California.
Eight parallel conferences include “Energy Harvesting and Storage”, “Photovoltaics” and “Electric Vehicles: Everything is Changing”.