Effects of All-Organic Interlayer Surface Modifiers on the Efficiency and Stability of Perovskite Solar Cells.

Surface imperfections created during fabrication of halide perovskite (HP) films could induce formation of various defect sites that affect device performance and stability. In this work, all-organic surface modifiers consisting of alkylammonium cations and alkanoate anions are introduced on top of the HP layer to passivate interfacial vacancies and improve moisture tolerance. Passivation using alkylammonium alkanoate does not induce formation of low-dimensional perovskites species. Instead, the organic species only passivate the perovskite's surface and grain boundaries, which results in enhanced hydrophobic character of the HP films. In terms of photovoltaic application, passivation with alkylammonium alkanoate allows significant reduction in recombination losses and enhancement of open-circuit voltage. Alongside unchanged short-circuit current density, power conversion efficiencies of more than 18.5 % can be obtained from the treated sample. Furthermore, the unencapsulated device retains 85 % of its initial PCE upon treatment, whereas the standard 3D perovskite device loses 50 % of its original PCE when both are subjected to ambient environment over 1500 h.

High-Pressure-Induced Comminution and Recrystallization of CH3 NH3 PbBr3 Nanocrystals as Large Thin Nanoplates.

High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (<10 nm) perovskite nanoplates, are retained and these exhibit simultaneous photoluminescence emission enhancing (a 15-fold enhancement in the photoluminescence) and carrier lifetime shortening (from ≈18.3 ± 0.8 to ≈7.6 ± 0.5 ns) after releasing of pressure from 11 GPa. This pressure-induced comminution of hybrid perovskite NCs and a subsequent amorphization-recrystallization treatment offer the possibilities of engineering the advanced hybrid perovskites with specific properties.