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Michael Hovish1 Florian Hilt1 Nicholas Rolston1 Karsten Bruening1 Reinhold Dauskardt1

1, Stanford University, Stanford, California, United States

Rapid Spray Plasma Processing (RSPP) is a high throughput, scalable route towards perovskite solar module manufacturing. In contrast to conventional spin-coating, RSPP uses clean dry air to produce a combination of plasma reactive species (photons, metastables, and radicals) and thermal energy which rapidly converts the perovskite film after spray-coating. High energy metastables and radical molecules diffuse through the thin plasma-liquid interface, inducing dissociation and volatilization of solvent molecules, and assisting the conversion into the perovskite structure. Deep UV photons emitted by the air plasma are absorbed by the DMF, superheating the solution. Convection with the plasma gas and reactive species quickly and efficiently transfers energy to the perovskite precursor-solvate, curing the film in a top-down manner. The result is a poly-disperse grain distribution, with grains ranging from 10s to 100s of nanometers in diameter, formed in under 250 milliseconds. We implemented in-situ wide angle x-ray scattering during single, double, and triple cation perovskite growth to further characterize the nucleation and growth mechanisms at play. The use of extremely bright synchrotron radiation and ultrafast detector speeds allowed us to resolve both direct crystallization and indirect crystallization reactions, indicated by transient peaks during the scattering measurement. The synergistic energy transfer from convection with the background gas and the interaction with plasma reactive species directly resulted in the mixed nucleation and growth reaction. We previously showed that the plasma annealing process caused significant mechanical toughening, with the current results suggesting that the mixed reaction pathway is responsible for the unique grain structure. Lab scale solar devices deposited with this method achieved excellent power conversion efficiencies (PCE) and large open circuit voltages (VOC) ; we observed 15.7% PCE for MAPbI3 and 1.08V VOC for Cs0.25FA0.75Pb(Br0.15I0.85)3 on PEDOT:PSS. The combination of high throughput manufacturing with excellent optoelectronic properties make RSPP very attractive to the single and multiple junction markets.

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