PTAA-poly[bis(4-phenyl)(2, 4, 6-trimethylphenyl)amine] – is an efficient hole transport material for perovskite solar cells, but can only be applied using spin-coating, which is not suitable for large areas, according to the research team. Blade coating is compatible with large areas, but the physical properties of PTAA prevent it from forming uniform layers when blade coated, leaving voids in the finished solar cell.
Knowing this, the team went in search of a hole haul compatible with the blade coating.
“We screened various hole transport materials and found that self-assembled monolayers are a promising class of materials for scaling up perovskite devices,” said Alex Jen, a professor at City University. of Hong Kong.
Selected molecules contain a chemical group that can naturally bind to the substrate, which can anchor the molecule, plus a chemical group at the other end that is easily wetted by the perovskite layer when applied, minimizing defect formation .
“In addition, since the self-assembled monolayer is a monolayer, charge carriers can be extracted efficiently from the perovskite to the substrate electrode through the charge tunneling effect, which improves the performance of the device,” added Jen.
The molecule can be solution processed and can be optimized for: better perovskite growth, improved defect density at its interface with the perovskite, and better energy band alignment with the perovskite.
A small (18cm2) proof-of-concept solar module showed 14% efficiency, and in an inert atmosphere, individual cells retained 90% of initial efficiency after 500 hours at 40°C.
The City University of Hong Kong worked with Shenzhen Southern University of Science and Technology on the project, which is covered in “Self-Assembled Monolayer Enabling Improved Buried Interfaces in Coated Perovskite Solar Cells”. blade for high efficiency and stability”, published by Nano Research Energy.