Observation of Internal Photoinduced Electron and Hole Separation in Hybrid Two-Dimentional Perovskite Films

Abstract

Two-dimensional (2D) organolead halide perovskites are promising for various optoelectronic applications. Here we report a unique spontaneous charge (electron/hole) separation property in multilayered (BA)(MA)PbI (BA = CH(CH)NH, MA = CHNH) 2D perovskite films by studying the charge carrier dynamics using ultrafast transient absorption and photoluminescence spectroscopy. Surprisingly, the 2D perovskite films, although nominally prepared as "n = 4", are found to be mixture of multiple perovskite phases, with n = 2, 3, 4 and ≈ ∞, that naturally align in the order of n along the direction perpendicular to the substrate. Driven by the band alignment between 2D perovskites phases, we observe consecutive photoinduced electron transfer from small-n to large-n phases and hole transfer in the opposite direction on hundreds of picoseconds inside the 2D film of ∼358 nm thickness. This internal charge transfer efficiently separates electrons and holes to the upper and bottom surfaces of the films, which is a unique property beneficial for applications in photovoltaics and other optoelectronics devices.

Benefiting from Spontaneously Generated 2D/3D Bulk‐Heterojunctions in Ruddlesden−Popper Perovskite by Incorporation of S‐Bearing Spacer Cation

“…[23] The Etgar team adjusted the n values to obtain quasi-3D perovskites (n = 40, 50, and 60), resulting in high open-circuit voltage (V OC ) and PCE. [28] In this work, we for the first time demonstrate a spontaneous generation of 2D:3D bulk-heterojunction structures at room temperature, in which 3D phases are epitaxially connected with 2D lattices by introducing S-bearing thiophene-2-ethylamine (C 6 H 9 NS, TEA) as an organic spacer. In addition, the solution processes would preferentially create a vertical cascade of stacked 2D phases with n values increasing from bottom (2D phases) to top (quasi-3D phases) during spin-casting.…”

“…The absorption edge of PEA perovskite films is significantly blue-shifted compared to TEA as shown in the inset of Figure 2a. [28] We further measured the Pb and S contents from top (surface) to bottom (interface with the substrate) of TEA samples by depth etching X-ray photoelectron spectroscopy (XPS) and the obtained atomic ratio of Pb:S is displayed in Figure S1 in the Supporting Information. Further evidence to the existence of 3D phases is provided by the PL spectra ( Figure 2b) where a significant red shift of the emission peak at 760 nm is found in TEA relative to PEA (728 nm).…”

Supramolecular Engineering for Formamidinium‐Based Layered 2D Perovskite Solar Cells: Structural Complexity and Dynamics Revealed by Solid‐State NMR Spectroscopy

“…The steady-state PL spectroscopy follows a similar trend, with well-defined emission signals ( Figure 2b). [22] However, the differences between the two spacers, A and A′, appear to be more profound, as further detailed in the subsequent analysis of their effects on the optoelectronic and structural features. This is also indicated www.advenergymat.de www.advancedsciencenews.com by the corresponding PL spectra featuring rather broad emissions ( Figure S5, Supporting Information).…”

Slow Hot‐Carrier Cooling in Halide Perovskites: Prospects for Hot‐Carrier Solar Cells

“…Furthermore, Ruddlesden-Popper perovskite quantum wells (QW) also have low thermal conductivity, internal self-charge carrier separation, and reduced charge recombination rate, [100] which will be beneficial for slow HC cooling and device operation. Furthermore, Ruddlesden-Popper perovskite quantum wells (QW) also have low thermal conductivity, internal self-charge carrier separation, and reduced charge recombination rate, [100] which will be beneficial for slow HC cooling and device operation.…”