Conformational disorder of organic cations tunes the charge carrier mobility in two-dimensional organic-inorganic perovskites

Abstract

The chemical nature of the organic cations governs the optoelectronic properties of two-dimensional organic-inorganic perovskites. But its mechanism is not fully understood. Here, we apply femtosecond broadband sum frequency generation vibrational spectroscopy to investigate the molecular conformation of spacer organic cations in two-dimensional organic-inorganic perovskite films and establish a correlation among the conformation of the organic cations, the charge carrier mobility, and broadband emission. Our study indicates that both the mobility and broadband emission show strong dependence on the molecular conformational order of organic cations. The gauche defect and local chain distortion of organic cations are the structural origin of the in-plane mobility reduction and broad emission in two-dimensional organic-inorganic perovskites. Both of the interlayer distance and the conformational order of the organic cations affect the out-of-plane mobility. This work provides molecular-level understanding of the conformation of organic cations in optimizing the optoelectronic properties of two-dimensional organic-inorganic perovskites.

Layered Perovskites in Solar Cells: Structure, Optoelectronic Properties, and Device Design

“…Advanced Energy Materials published by Wiley-VCH GmbH being reported. Interestingly, the hole mobility of about 2 × 10 -4 cm 2 V −1 s −1 obtained for the shortest barrier length of 1.4 nm is quite similar to the above discussed study by Li et al, [18] whilst the electron mobility is consistently one order of magnitude lower.…”

“…[244] This is indeed the case for linear aliphatic spacers with varied length, as shown by Li et al Here, both in-plane and out-of-plane charge carrier mobility clearly increases with the reduction of interlayer distance, with the exception of BA 2 PbI 4 . [18] From the series of n-alkyl cations, Li et al found hexylammonium HA to show the highest in-plane (1.5 cm 2 V −1 s −1 ) and out-of-plane mobility (3 × 10 -4 cm 2 V −1 s −1 ) due to the combination of low interlayer distance and non-distorted carbon chain, as further discussed in below. [18] For LPKs based on aromatic spacers SCLC measurements also show a trend of increase in both hole and electron mobilities with the reduction in d-spacing.…”

“…[18] From the series of n-alkyl cations, Li et al found hexylammonium HA to show the highest in-plane (1.5 cm 2 V −1 s −1 ) and out-of-plane mobility (3 × 10 -4 cm 2 V −1 s −1 ) due to the combination of low interlayer distance and non-distorted carbon chain, as further discussed in below. [18] For LPKs based on aromatic spacers SCLC measurements also show a trend of increase in both hole and electron mobilities with the reduction in d-spacing. [245] Although not clearly specified, the device architecture and crystal orientation suggest that it is the out-of-plane mobility www.advancedsciencenews.com…”

“…[15] Here, the limiting factor is inefficient charge transport across the organic interlayer, currently preventing the full exploitation of the layered structure in PSCs.This can be approached in two ways, either by keeping the LPK layer very thin, currently the most popular approach, or by increasing the electrical conductivity of the material. [18,19] The conductivity can be enhanced through increasing the number of inorganic layers n, but this comes at the price of reduced stability. [20][21][22] The better approach is to enhance the charge transport in LPKs through the molecular engineering of the organic Layered hybrid perovskites (LPKs) have emerged as a viable solution to address perovskite stability concerns and enable their implementation in wide-scale energy harvesting.…”

Charge Carrier Dynamics in Sn-Doped Two-Dimensional Lead Halide Perovskites Studied by Terahertz Spectroscopy

“…The merit suggests the 2D perovskites are particularly suitable for application of light-emitting diodes (LEDs). In 2D perovskites, a broadband emission with large stokes shift is also observed, which is proposed for the potential applications of white light display and lightening (Dohner et al, 2014a,b;Smith et al, 2017;Smith and Karunadasa, 2018;Li C. et al, 2020). In addition to efficient light emission, the transport of charge carriers is also pivotal for the performance of an optoelectronic device which, however, is limited in 2D perovskites.…”