In layered two-dimensional(2D)perovskites,the inorganic perovskite layers sandwiched between cation spacers create quantum well(QW)structures,showing large exciton binding energies that hinder the efficient dissociati...In layered two-dimensional(2D)perovskites,the inorganic perovskite layers sandwiched between cation spacers create quantum well(QW)structures,showing large exciton binding energies that hinder the efficient dissociation of excitons into free carriers.This leads to poor carrier transport properties and low-performance light-conversion-based devices,and the direct understanding of the underlying physics,particularly concerning surface states,remains extremely difficult,if not impossible,due to the challenges in real-time accessibility.Here,we utilized four-dimensional scanning ultrafast electron microscopy(4D-SUEM),a highly sensitive technique for mapping surface carrier diffusion that diverges from those in the bulk and substantially affects material properties.We directly visualize photo-generated carrier transport over both spatial and temporal dimensions on the top surface of 2D perovskites with varying inorganic perovskite layer thicknesses(n=1,2,and 3).The results reveal the photo-induced surface carrier diffusion rates of~30 cm^(2)·s^(-1)for n=1,~180 cm^(2)·s^(-1)for n=2,and~470 cm^(2)·s^(-1)for n=3,which are over 20 times larger than bulk.This is because charge carrier transmission channels have much wider distributions on the top surface compared to the bulk,as supported by the Density Functional Theory(DFT)calculations.Finally,our findings represent the demonstration to directly correlate the discrepancies between surface and bulk carrier diffusion behaviors,their relationship with exciton binding energy,and the number of layers in 2D perovskites,providing valuable insights into enhancing the performance of 2D perovskite-based optoelectronic devices through interface engineering.展开更多
基金funded by King Abdullah University of Science and Technology(KAUST)the financial support provided by the Key Scientific Research Project of Colleges and Universities in He’nan Province(Grant No.24A140022)+2 种基金the National Natural Science Foundation of China(Grant No.12347160)the funding support from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project no.PolyU25300823)Hong Kong Polytechnic University(Grant no.P0042930).
文摘In layered two-dimensional(2D)perovskites,the inorganic perovskite layers sandwiched between cation spacers create quantum well(QW)structures,showing large exciton binding energies that hinder the efficient dissociation of excitons into free carriers.This leads to poor carrier transport properties and low-performance light-conversion-based devices,and the direct understanding of the underlying physics,particularly concerning surface states,remains extremely difficult,if not impossible,due to the challenges in real-time accessibility.Here,we utilized four-dimensional scanning ultrafast electron microscopy(4D-SUEM),a highly sensitive technique for mapping surface carrier diffusion that diverges from those in the bulk and substantially affects material properties.We directly visualize photo-generated carrier transport over both spatial and temporal dimensions on the top surface of 2D perovskites with varying inorganic perovskite layer thicknesses(n=1,2,and 3).The results reveal the photo-induced surface carrier diffusion rates of~30 cm^(2)·s^(-1)for n=1,~180 cm^(2)·s^(-1)for n=2,and~470 cm^(2)·s^(-1)for n=3,which are over 20 times larger than bulk.This is because charge carrier transmission channels have much wider distributions on the top surface compared to the bulk,as supported by the Density Functional Theory(DFT)calculations.Finally,our findings represent the demonstration to directly correlate the discrepancies between surface and bulk carrier diffusion behaviors,their relationship with exciton binding energy,and the number of layers in 2D perovskites,providing valuable insights into enhancing the performance of 2D perovskite-based optoelectronic devices through interface engineering.
