Researchers from Peking University in China have developed a manufacturing method for perovskite solar cells using a pre-nucleation technique. Compared to traditional solvent dripping methods, the approach enables the creation of smaller crystallites in the perovskite films as uncontrolled crystallite growth affects the efficiency and durability of cells.

The technique aims to avoid the efficiency loss caused by humidity linked to the interactions of ambient water and oxygen with the perovskite precursors and substrate used during cell production.

Pre-nucleation consists of the controlled formation of a vast number of lead complexes – “pre-nucleation clusters” – during the wet sample spinning process of perovskite film manufacture.

The new approach was developed as a way to design chemical reaction routes, according to the researchers. “Although these chemical reaction routes showed potential to realize the ambient fabrication of PVSCs [PV solar cells], the inherent mechanisms are still unclear and the variations of device performance to environmental conditions need to be improved,” stated the group.

The researchers said the formation of lead complexes is facilitated by the presence of water in conventional manufacturing processes. To avoid the presence of excess water, the Peking group used a burst of lead complexes to facilitate, and prolong, nucleation of the intermediate crystallites. Uncontrolled growth of such crystallites can affect the efficiency and durability of solar cells.

Unlike the conventional method of solvent dripping in ambient air, which leads to large intermediate crystals, the method proposed by the Peking group is said to deliver smaller crystals in the wet films which are easier to convert into perovskite. “As a result, the pre-nucleation method made the wet film transform more easily and more rapidly from the transparent intermediate to the [more efficient] black perovskite [form], even without annealing,” the researchers said, referring to the process of heating and then slowly cooling to increase durability.

The Peking group claims this process has enabled the production of a perovskite cell with a peak conversion efficiency of 21.5% and an average of 18.8%. In durability terms, the researchers said the cell lost around 10% of its efficiency after 100 days of storage.