skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Resolving in-plane and out-of-plane mobility using time resolved microwave conductivity
The contactless characterization technique time resolved microwave conductivity (TRMC) provides a means to rapidly and unambiguously approximate carrier mobilities and lifetimes for a variety of semiconducting materials. When using a cavity-based approach however, the technique can conventionally only resolve carrier mobilities in the plane of the substrate. In solar cells, charge carriers are extracted in the direction perpendicular to the substrate, therefore it would be beneficial if one were able to evaluate the mobility in this direction also. Here we present a novel approach for resolving charge carrier mobilities in different planes within a sample. Using a range of 3D-printed sample holders, where the sample is held at various angles relative to the incident light, we are able to simultaneously resolve the mobility in the plane of the sample and out of the plane of the sample. As examples, we have studied the 3-dimensional corner-connected metal halide perovskite methylammonium lead iodide and the 2-dimensional perovskite precusor, lead iodide.  more » « less
Award ID(s):
1902032
PAR ID:
10233885
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Journal of Materials Chemistry C
Volume:
8
Issue:
31
ISSN:
2050-7526
Page Range / eLocation ID:
10761 to 10766
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; (, Advanced Materials)
    Abstract The first experimental realization of the intrinsic (not dominated by defects) charge conduction regime in lead‐halide perovskite field‐effect transistors (FETs) is reported. The advance is enabled by: i) a new vapor‐phase epitaxy technique that results in large‐area single‐crystalline cesium lead bromide (CsPbBr3) films with excellent structural and surface properties, including atomically flat surface morphology, essentially free from defects and traps at the level relevant to device operation; ii) an extensive materials analysis of these films using a variety of thin‐film and surface probes certifying the chemical and structural quality of the material; and iii) the fabrication of nearly ideal (trap‐free) FETs with characteristics superior to any reported to date. These devices allow the investigation of the intrinsic FET and (gated) Hall‐effect carrier mobilities as functions of temperature. The intrinsic mobility is found to increase on cooling from ≈30 cm2V−1s−1at room temperature to ≈250 cm2V−1s−1at 50 K, revealing a band transport limited by phonon scattering. Establishing the intrinsic (phonon‐limited) mobility provides a solid test for theoretical descriptions of carrier transport in perovskites, reveals basic limits to the technology, and points to a path for future high‐performance perovskite electronic devices. 
    more » « less
  2. ; ; ; ; ; (, Nanoscale)
    null (Ed.)
    Although 2D materials have been widely studied for more than a decade, very few studies have been reported on the in-plane structure domain (STD) size even though such a physical property is critical in determining the charge carrier and energy carrier transport. Grazing incidence X-ray diffraction (XRD) can be used for studying the in-plane structure of very thin samples, but it becomes more challenging to study few-layer 2D materials. In this work the nanosecond energy transport state-resolved Raman (nET-Raman) technique is applied to resolve this key problem by directly measuring the thermal reffusivity of 2D materials and determining the residual value at the 0 K-limit. Such a residual value is determined by low-momentum phonon scattering and can be directly used to characterize the in-plane STD size of 2D materials. Three suspended MoSe 2 (15, 50 and 62 nm thick) samples are measured using nET-Raman from room temperature down to 77 K. Based on low-momentum phonon scattering, the STD size is determined to be 58.7 nm and 84.5 nm for 50 nm and 62 nm thick samples, respectively. For comparison, the in-plane structure of bulk MoSe 2 that is used to prepare the measured nm-thick samples is characterized using XRD. It uncovers crystallite sizes of 64.8 nm in the (100) direction and 121 nm in the (010) direction. The STD size determined by our low momentum phonon scattering is close to the crystallite size determined by XRD, but still shows differences. The STD size by low-momentum phonon scattering is more affected by the crystallite sizes in all in-plane directions rather than that by XRD that is for a specific crystallographic orientation. Their close values demonstrate that during nanosheet preparation (peeling and transfer), the in-plane structure experiences very little damage. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Materials)
    Abstract Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge‐transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5‐bis(3‐dodecyl‐2‐thienyl)‐thiazolo[5,4‐d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility. Films are analyzed by X‐ray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field‐effect transistors are five times higher when the crystals are grown with the smallest pitches (most twisted), compared to those with the largest pitches, along the fiber elongation direction. A tenfold increase is observed along the perpendicular direction. Simulation of electrical potential based on scanning electron microscopy images and density functional theory suggests that the twisting‐enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permit better charge transport over the film surface compared to fewer big crystallites separated by larger gaps. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Energy Materials)
    Abstract Formamidinium (FA)‐based lead iodide perovskites have emerged as the most promising light‐absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the phase‐instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA‐based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA‐based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but also enhances the charge‐carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment‐theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000‐h storage under ambient conditions. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, ACS Nano)
    Understanding and characterizing the intrinsic properties of charge carrier transport across the interfaces in van der Waals heterostructures is critical to their applications in modern electronics, thermoelectrics, and optoelectronics. However, there are very few published cross-plane resistivity measurements of thin samples because these inherently 2-probe measurements must be corrected for contact and lead resistances. Here, we present a method to extract contact resistances and metal lead resistances by fitting the width dependence of the contact end voltages of top and bottom electrodes of different linewidths to a model based on current crowding. These contributions are then subtracted from the total 2-probe cross-plane resistance to obtain the cross-plane resistance of the material itself without needing multiple devices and/or etching steps. This approach was used to measure cross-plane resistivities of a (PbSe)1(VSe2)1 heterostructure containing alternating layers of PbSe and VSe2 with random in-plane rotational disorder. Several samples measured exhibited a 4 order of magnitude difference between cross-plane and in-plane resistivities over the 6–300 K temperature range. We also reported the first observation of charge density wave transition in the cross-plane transport of (PbSe)1(VSe2)1 heterostructure. The device fabrication process is fully lift-off compatible, and the method developed enables the straightforward measurement of the resistivity anisotropy of most thin film materials with nm thicknesses. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email