| In the past few years,inorganic-organic hybrid perovskite material possessing amazing advantages including large absorption coefficient,weak exciton binding energy,long and balanced electron-hole diffusion length and so on has been widely recognized as one promising material in the field of photovoltaics,where the emerging multicomponent perovskite(mperovskite)is gradually predominating the field by virtue of tunable optoelectronic properties and superior stability compared with mono-cation and mono-anion perovskite.Mixedcomposition perovskite solar cells(m-PSCs)are at the frontier of photovoltaic technology up to now and the power conversion efficiency of them already exceeded 22%.Wherein,the study of the crystal growth engineering with respect to m-perovskite film is believed an effective way to further decrease the energy loss.So far,many strategies have been undertaken to prepare high-quality m-perovskite films by spin-coating,among which the anti-solvent assisted crystallization has been widely accepted as an feasible method to prepare perovskite films with pure and stable crystal phase and excellent surface coverage.In practice,the formation of mperovskite film during the transitory one-step spin-coating is a train of complex dynamic processes that are intimately bound up with solvent evaporation and anti-solvent interdiffusion.However,few research has paid enough attention to the vital role of solvent behavior during spin-coating process to the quality of m-perovskite film.The air flow velocity around the substrate during spin-coating will undoubtedly have a noticeable impact on the mode of the solvent volatilization and anti-solvent diffusion,which will lead to entirely different crystallization process and final quality of of m-perovskite film.In this paper,the air flow velocity during spin-coating was proved to be a very important variable.We modified the spin-coating machine by home-made metal disk with fan blades to produce strong air turbulence.A high air flow velocity(HAFV)with an order of magnitude enhancement could be generated during rotation by means of our specific modification and we further confirmed the existence of a gradient pressure distribution over the plane of the customized metal disk during rotation.Such pressure gradient distribution along radial direction would generate a consecutive air flow from the surrounding area to the center point of our sample and spontaneously an evident negative pressure zone was formed in the very center of the disk where our sample located.HAFV accompanied with central negative pressure zone could significantly facilitate the evaporation of solvent molecules during spin-coating,which in turn would remarkably polish the kinetic processes as to the formation of m-perovskite.To elucidate the mechanism of the modification of HAFV,we divided the one-step spin-coating process into two subprocesses and in each subprocess the diverse mechanisms of air flow velocity on the crystallization of m-perovskite were adequately revealed.A precise control over the formation as well as decomposition of intermediate phase was realized through HAFV,which yielded a large number of highly ordered seed crystals.Such seed crystals with uniform preferential orientation as well as even distribution on the substrate trended to produce a compact m-perovskite film with better coverage,larger crystal grains,and less bulk and surface defects.Characterization results further illustrated that the elaborate modification of HAFV is indeed a simple and effective approach to substantially restrain defected induced charge recombination.The best-performance planar-structured m-PSC exhibited a power conversion efficiency of 20.24%(stabilized output efficiency of 19.58%).The long-term stability was greatly improved as well.Our work opens a new avenue to improving the properties of mperovskite film. |
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