Enhanced Charge Transport in 2D Perovskites via Fluorination of Organic Cation

Abstract

Organic-inorganic halide perovskites incorporating two-dimensional (2D) structures have shown promise for enhancing the stability of perovskite solar cells (PSCs). However, the bulky 2D cations often limit charge transport. Here, we report on a simple approach based on molecular design of the organic 2D spacer to improve the transport properties of 2D perovskites, and we use phenethylammonium (PEA) as an example. We demonstrate that by fluorine substitution on the para position in PEA to form 4-fluoro-phenethylammonium (F-PEA), the average phenyl ring centroid-centroid distances in the organic layer become shorter with aligned stacking of perovskite sheets. The impact is enhanced orbital interactions and charge transport across adjacent inorganic layers as well as increased carrier lifetime and reduced trap density. Using a simple perovskite deposition at room temperature without using any additives, we obtained power conversion efficiency >13% for (F-PEA)2MA4Pb5I16 based PSCs. In addition, the thermal stability of 2D PSCs based on F-PEA is significantly enhanced compared to those based on PEA.

Interlayer Cross‐Linked 2D Perovskite Solar Cell with Uniform Phase Distribution and Increased Exciton Coupling

“…But to date, the insulating ligands, i.e., BA ( n ‐butylammonium) and PEA (phenethylammonium), are mostly investigated by researchers to form Ruddelsden–Popper (RP) phase 2D perovskites . RP phase 2D perovskites are attractive for several reasons: First, the solution‐processed 2D perovskite film exhibits the unique multicomponent quantum wells (MQW) structure that could naturally confine excitons, showing their enormous potential in light emitting diode (LED) applications . Second, the orientation of 2D slices could be altered perpendicular to the substrates to facilitate charge collection efficiency with many methods, such as hot‐casting NH 4 SCN or NH 4 Cl additive assisting .…”

Enhanced Charge Transport by Incorporating Formamidinium and Cesium Cations into Two‐Dimensional Perovskite Solar Cells

“…[5] This feature makes 2D perovskites promising candidates for optoelectronic devices that require long-term chemical stability. [10] Studies have shown that cesium (Cs) ions are effective in assisting the crystallization of perovskite because of the entropic stabilization. Nevertheless,s ome unfavorable characteristics have been identified, such as the undesired orientation of the layered structures in 2D PSCs,o rientations which can cause chargetransport problems leading to charge accumulation and recombination losses.…”

“…Nevertheless,s ome unfavorable characteristics have been identified, such as the undesired orientation of the layered structures in 2D PSCs,o rientations which can cause chargetransport problems leading to charge accumulation and recombination losses. [10] Studies have shown that cesium (Cs) ions are effective in assisting the crystallization of perovskite because of the entropic stabilization. [11] By doping the Cs + cation into a2 D BA 2 MA 3 Pb 4 I 13 perovskite layer, Liu et al reported aPCE of 13.7 %based on ahot-casting method.…”

Manipulation of Dipolar Polarization at Steady States for a Quasi‐2D Organic–Inorganic Hybrid Perovskite with a Nanorod Network

“…Table summarizes a few works with their photovoltaic parameters. In those, some particular treatments were adopted to improve the mobility and grain size of 2D perovskite films, for example, chlorination of organic ammonium salt, fluorination of PEA, and addition of an organic additive such as ammonium thiocyanate (NH 4 SCN) . Our quasi‐2D perovskite solar cell with high performance is indeed partly ascribed to the unique feature of the nanorod network.…”

“…The photoactive layer, quasi‐2D (PEA) 2 (MA) 3 Pb 4 I 13 , exhibits a large‐area nanorod network. The device produces a relatively high short‐circuit current of 18.4 mA cm −2 and an open‐circuit voltage ( V oc ) of 1.07 V at the same time, with a PCE of 14.1% by comparison with other works . In nondestructive impedance spectroscopy for in situ characterization at both steady states and short‐circuit‐current conditions, the quasi‐2D (PEA) 2 (MA) 3 Pb 4 I 13 shows remarkable photo‐ and electrical responses at some steady states under AC excitation frequencies.…”