Preparation Of Ultrathin Nanosheets Based On Layered Double Hydroxides And Their Enhancement Of Perovskite Crystallization

Perovskite solar cells（PSCs）have emerged as a potential alternative to crystalline silicon solar cells due to their excellent photovoltaic performance and simple manufacturing process.Over the past few years,the improvement in performance has greatly benefited from the emergence of high quality perovskite（PVK）film manufacturing processes.During the conversion process from precursor solution to PVK film,controlled nucleation and crystal growth can directly affect the quality of PVK film.Among the many quality improvement methods,the introduction of ultra thin two dimensional nanosheets has unique advantages.For example,superior carrier mobility,adjustable band gap,easy-to-functionalize surface and strong chemical stability can effectively regulate PVK crystal growth,passivate PVK interface and grain boundary defects,and improve carrier extraction and transmission rates,thereby effectively improving the photoelectric conversion efficiency and long term stability of the device.Therefore,ultrathin layered double hydroxides nanosheets（LDHs-NS）and ultra-thin carbon nitride nanosheets（CN-NS）were prepared by one step synthesis and space constrained synthesis respectively,which comprehensively improved the photoelectric conversion efficiency and thermal stability of PSCs by regulating the growth of PVK crystals,accelerating the separation of carriers,improving the extraction and transport rate of carriers,reducing defects and releasing interfacial stresses.The specific research content is as follows:（1）LDHs-NS was prepared by one step synthesis,and the macroscopic and microscopic anisotropy of LDHs-NS was used to regulate the orderly growth of PVK crystals,improve the quality of PVK crystals,and optimize the photoelectric properties and charge transport kinetic characteristics of PVK films.First of all,LDHs-NS has excellent mechanical flexibility and optical transparency,which does not affect the light absorption of PVK film.Secondly,LDHs-NS surfaces have a rich,highly ordered arrangement of hydroxyl groups（–OH）that can interact with Pb²⁺in PVK precursor solutions.Molecules or ions adsorbed on the surface of LDHs-NS serve as sites for future crystal nucleation growth.Finally,in the spin coating process,LDHs-NS is more inclined to be tiled on the substrate under the action of centrifugal force,and with the volatilization of the solvent,PVK crystals grow along the LDHs-NS crystal plane,so that PVK crystals have an optimal orientation.The optimal orientation of PVK crystal can effectively promote carrier transport,reduce carrier recombination at interface and grain boundaries,the carbon-based PSCs treated with all air treatment achieve a photoelectric conversion efficiency of 12.26%,and the device stability is greatly improved.（2）Using the two-dimensional confined space of LDHs materials,CN-NS was synthesized with a limited domain.Compared with the bulk CN prepared by the traditional calcination method,CN-NS has a narrow band gap and strong carrier separation and transport capabilities.The abundant functional groups（–NH₂ and–OH）on the surface of CN-NS bond to PVK,slowing down ion migration in PVK films and providing a prerequisite for the formation of high-quality PVK crystals.CN-NS is rejected to the PVK grain boundary during annealing and can be used as a carrier transporter to promote charge separation and extraction,and the synergistic effect makes the carbon-based PSCs treated with all air reach a photoelectric conversion efficiency of 12.57%.