Meniscus-assisted solution printing of high-quality perovskite thin films with high optoelectronic performance.Researchers have developed a new way to more easily produce perovskite films by enhancing power conversion efficiencies to almost 20% through managing both crystal size and orientation. An innovative low-temperature solution printing technique called meniscus-assisted solution printing (MASP) allowed the fabrication of high-efficiency perovskite solar cells with large crystals that work to minimize grain boundaries.
As discussed in Nature Communications [He et al. Nat. Commun. (2017) DOI: 10.1038/ncomms16045], the process uses parallel plates to produce a meniscus of ink with metal halide perovskite precursors that could be scaled up to quickly develop large areas of dense crystalline film on a variety of substrates. The operating parameters for the fabrication process were based on a kinetics study of perovskite crystals observed throughout their formation and growth cycle.
MASP improves on other thin-film coating techniques such as doctor-blading since the meniscus effect is the primary driving force for solvent evaporation and solute crystallization rather than thermal evaporation. The technique could be used in flexible solar cells and other applications that require a low-temperature continuous fabrication process, especially as it could be scaled up to offer high-throughput, large-scale perovskite films.
“We successfully scrutinized the crystal growth kinetics of the perovskite film during MASP for the first time, providing a better understanding of morphology and crystallinity controls during the solution-processing deposition”Zhiqun Lin
The team therefore developed a way to use capillary action to draw perovskite ink into a meniscus formed between two almost parallel plates, with the lower plate moving continuously so that solvent evaporates at the meniscus edge to produce crystalline perovskite. As these crystals form, further ink is pulled into the meniscus.
To determine the best rate for moving the plates, the distance between them and the temperature that should be applied to the lower plate, the growth of perovskite crystals during MASP was assessed. It was found that crystals begin to grow at a quadratic rate before slowing to a linear rate as they impact on their neighbors. The process generates quite large crystals that cover the substrate surface – as they possess a dense structure and less crystals, there are fewer gaps to constrain current flow, reducing the number of boundaries.
They also identified the optimal window for MASP deposition of perovskite thin films, and outlined the effects of temperature, coating speed and meniscus geometry on the crystallization. As researcher Zhiqun Lin said, “We successfully scrutinized the crystal growth kinetics of the perovskite film during MASP for the first time, providing a better understanding of morphology and crystallinity controls during the solution-processing deposition.”
They now hope to fabricate the films on polymer substrates, assess other unique properties such as thermal and piezotronic, and also examine the MASP deposition of the electron-transport layer and the hole-transport layer over large areas for perovskite solar cells.