Tuning Nucleation Sites to Enable Monolayer Perovskite Films for Highly Efficient Perovskite Solar Cells

Abstract

The nucleation site plays a critical role in achieving the full coverage of perovskite film at both the macroscopic and microscopic scales, and it is systematically investigated for the first time in this study. The results show that under natural conditions, the incomplete coverage of perovskite film is due to both heterogeneous nucleation and homogeneous nucleation. The established concentration field and temperature field in the precursor solution show that there are two preferential nucleation sites, i.e., the upper surface of the precursor solution (homogeneous nucleation) and the surface of the substrate (heterogeneous nucleation). The nucleation sites are tuned by decreasing the drying pressure from the atmosphere to 3000 Pa, and then to 100 Pa, and then the microstructures of the perovskite films change from an incomplete coverage state to a monolayer full coverage state, and then to a bilayer full coverage state. At last, when the full coverage perovskite films are assembled into perovskite solar cells, the photovoltaic performance of the monolayer perovskite solar cells is slightly greater than that of the bilayer perovskite solar cells. The electrochemical characterization shows that there is more restrained internal recombination of the monolayer perovskite solar cells compared with bilayer perovskite solar cells.

Vapor Exchange Deposition of an Air-Stable Lead Iodide Adduct on 19% Efficient 1.8 cm2 Perovskite Solar Cells

“…Further, a double-layered perovskite structure is formed in films that are thicker than 500 nm. Such cross-sectional characteristics are most likely to be the consequences of simultaneous nucleation at the top and bottom surfaces . In VASP, grains are formed via sequential nucleation, crystallization, and Ostwald ripening. − When hot MAI molecules adsorb on PbI 2 , MAPbI 3 crystallites spontaneously form on the top surface, and meanwhile nucleation also occurs at the bottom surface where the active energy for nucleation is lower.…”

Flexible Perovskite Solar Cells with Enhanced Performance Based on a Void-Free Imbedded Interface via a Thin Layer of Mesoporous TiO2

“…When perovskite films were deposited by the one-step spin-coating method, nucleation occurs right after the drop of an antisolvent and the resulting supersaturation in the residual solution. On the smooth and dense bl-SnO 2 substrate, homogeneous nucleation first occurs on the top zone of the precursor solution induced by the evaporation of the solvent. − During the subsequent crystal growth process, the supersaturation on the top zone was still higher than that on the bottom zone due to the continuous evaporation of the solvent. On the other hand, there are few nucleation sites and low supersaturation on the bottom of the precursor solution .…”

Impact of Delay Time before Annealing MAI-PbI2-DMSO Intermediate Phase on Perovskite Film Quality and Photo-Physical Properties

“…With the extension of the delay time before annealing, the grain size becomes Crystals 2019, 9, 151 5 of 9 smaller, and the phenomenon of stacking will appear, which is consistent with the trend of changes in the SEM images measured for different delay times, indicating that the surface of the film deteriorates with the extension of the delay time before the annealing of the perovskite film. The SEM images show that more nuclei are generated during the drying process, the grain size might be decreases and the stack grows, resulting in an increase in the number and surface roughness of the perovskite film pin-holes [14,20]. the delay time is 0 s, the crystal grains forming the perovskite are relatively large, and the crystal grains are uniform without overlap.…”