Using Metal Nanoparticles to improve the efficiency of Perovskite Solar Cells fabricated in air

Solar energy and in particular next generation photovoltaics are often identified as fundamental factors in the development of a sustainable and renewable future. The next generation of solar energy is being revolutionised by perovskites, a class of materials characterised by low costs, outstanding optical and electrical properties, and defect resistance. However, some challenges remain, e.g. the performance and the stability of transport layers, and stringent requirements for an inert atmosphere during perovskite deposition. This project aims to develop and test strategies to overcome these limitations, in order to accelerate the application of perovskites into the solar cell market.
Here, metal nanoparticles were successfully fabricated via both chemical and physical methods, then incorporated inside transport layers, that were optimised from the points of view of fabrication technique, deposition parameters, and optoelectronic properties. Integration of metal nanoparticles inside perovskite solar cells increased their efficiency from 13.4+-0.4% to 14.3+-0.3%, and, thanks to time resolved photoluminescence, this improvement was attributed to the enhanced charge carrier transfer and extraction via the composite transport layer.
New techniques for the deposition of perovskite thin films by spin-coating in air were developed. These techniques introduced a preliminary step before the annealing of perovskite, either an annealing at reduced temperature, or a vacuum treatment. Consequently, the nucleation rate was increased, and the growth of grains happened more gradually. Perovskite grown via these techniques exhibited improved crystallinity (reduced microstrains and defects in the lattice) and morphology (better interfaces with overlying layers). Finally, these high-quality perovskite layers deposited in ambient air were used to fabricate devices with an efficiency of 15.3 +- 0.9% (maximum efficiency 16.7%), closer to the record in the literature for CH3NH3PbI3 in controlled atmospheres, i.e. in gloveboxes (20%). In conclusion, these strategies will help to increase the efficiency and decrease the cost of solar cells, and they have applications beyond photovoltaics, in many devices where electronic properties have a primary relevance.