Discerning the Surface and Bulk Recombination Kinetics of Organic-Inorganic Halide Perovskite Single Crystals

摘要

Organic-inorganic halide perovskite single crystals possess many outstanding properties conducive for photovoltaic and optoelectronic applications. However, a clear photophysics picture is still elusive, particularly, their surface and bulk photophysics are inexorably convoluted by the spectral absorbance, defects, coexisting photoexcited species, etc. In this work, an all-optical study is presented that clearly distinguishes the surface kinetics from those of the bulk in the representative methylammonium-lead bromide (MAPbBr(3)) and -lead iodide (MAPbI(3)) single crystals. It is found that the bulk recombination lifetime of the MAPbBr(3) single crystal is shortened significantly by approximately one to two orders (i.e., from approximate to 34 to approximate to 1 ns) at the surface with a surface recombination velocity of around 6.7 x 10(3) cm s(-1). The surface trap density is estimated to be around 6.0 x 10(17) cm(-3), which is two orders larger than that of the bulk (5.8 x 10(15) cm(-3)). Correspondingly, the diffusion length of the surface excited species is approximate to 130-160 nm, which is considerably reduced compared to the bulk value of approximate to 2.6-4.3 mu m. Furthermore, the surface region has a wider bandgap that possibly arises from the strong lattice deformation. The findings provide new insights into the intrinsic photophysics essential for single crystal perovskite photovoltaics and optoelectronic devices.