Double Charged Surface Layers in Lead Halide Perovskite Crystals

Abstract

Understanding defect chemistry, particularly ion migration, and its significant effect on the surface's optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.

Single-crystalline perovskite wafers with a Cr blocking layer for broad and stable light detection in a harsh environment

“…1a and S2 † give the surface and crosssection scanning electron microscopy (SEM) images of the fabricated MAPbI 3 wafer. The surface morphology of the singlecrystalline MAPbI 3 wafer shows some nano-grain boundaries as reported by Mohammed et al, 39 which is very possibly due to the surface hydration and disorder facilitating the ion migration in…”

Recent Development of Organic-Inorganic Perovskite-Based Tandem Solar Cells

“…Another key challenge for perovskite‐based tandem cells is the long‐term stability of perovskite subcells, whereas a continuous innovation in materials processing, device design, fabrication, and yield is required to ensure them to become viable. Endeavors have been made in understanding the defect generation and the origin of instability of the traditional perovskite materials, in which the ion migration is usually believed to play a crucial role . In view of the perovskite materials integrated into tandem cells, new types of perovskite materials, e.g., 2D or quasi‐2D structure with long chain spacer layers, are theoretically proven to be excellent candidates for concurrently addressing the stability and performance concerns of the current perovskite tandem cells.…”

Charge Transport in Halide Perovskite Single Crystals: Experimental and Theoretical Perspectives

“…Similarly, the termination of crystal structure at the surface introduces various new phenomenon in the properties of HaPs (Figure (a)): the presence of surface double charge layers, surface restructuring into a polycrystalline‐like layer, for example. In particular, the surface recombination velocity of single crystal HaPs has been found to be faster than the bulk value, but 2–3 orders of magnitude slower than that of traditional semiconductors ,…”

“…In particular, the surface recombination velocity of single crystal HaPs has been found to be faster than the bulk value, but 2-3 orders of magnitude slower than that of traditional semiconductors. [95,96] The device application of HaP surface effects has also been explored: The surface recombination has been used by Fang et al to narrow the spectral response of single crystal MAPbBr 3 photodetectors, [97] and the high sensitivity of HaP surface photoluminescence to environmental gas has been suggested by Fang et al to have potential in gas sensors. [98],…”