Localized Charges Control Exciton Energetics and Energy Dissipation in Doped Carbon Nanotubes

Abstract

Doping by chemical or physical means is key for the development of future semiconductor technologies. Ideally, charge carriers should be able to move freely in a homogeneous environment. Here, we report on evidence suggesting that excess carriers in electrochemically p-doped semiconducting single-wall carbon nanotubes (s-SWNTs) become localized, most likely due to poorly screened Coulomb interactions with counterions in the Helmholtz layer. A quantitative analysis of blue-shift, broadening, and asymmetry of the first exciton absorption band also reveals that doping leads to hard segmentation of s-SWNTs with intrinsic undoped segments being separated by randomly distributed charge puddles approximately 4 nm in width. Light absorption in these doped segments is associated with the formation of trions, spatially separated from neutral excitons. Acceleration of exciton decay in doped samples is governed by diffusive exciton transport to, and nonradiative decay at charge puddles within 3.2 ps in moderately doped s-SWNTs. The results suggest that conventional band-filling in s-SWNTs breaks down due to inhomogeneous electrochemical doping.

Quantifying Doping Levels in Carbon Nanotubes by Optical Spectroscopy

“…More details about the electrochemical setup can be found elsewhere. 14,20 Suspensions with redox-chemically doped s-SWNTs were prepared using the same starting material as for electrochemical measurements. To provide sufficiently good solubility for gold(III)-chloride (Sigma-Aldrich) we used a 5:1 toluene to acetonitrile solvent mixtures for s-SWNTs and redox agent alike.…”

Customizing the Polarity of Single‐Walled Carbon‐Nanotube Field‐Effect Transistors Using Solution‐Based Additives

“…The PL of the S 11 s‐SWNTs is completely quenched which indicates the opening of a very efficient non‐radiative recombination channel when F 4 ‐TCNQ is present. This might be related to the formation of trions 38. However, F 4 ‐TCNQ appears not only to interact with the carbon nanotubes but also to disrupt the wrapping of the polymer and to interact directly with the polymer chains.…”

“…Figure a shows the R c as a function of gate voltage measured using the transfer line method38 for the reference device, and for the FETs containing 15 µ m BV or 370 µ m N‐DMBI. The R c of the FET containing 370 µ m N‐DMBI shows a slight decrease to 1098 ohm·cm (at V G = 6 V) from the value of 1237 ohm·cm (at V G = 6 V) for the reference device.…”

“…This might be related to the formation of trions. [38] However, F 4 -TCNQ appears not only to interact with the carbon nanotubes but also to disrupt the wrapping of the polymer and to interact directly with the polymer chains. As mentioned above, larger absorption from P3DDT isolated chains upon addition of F 4 -TCNQ is appearing.…”

“…In order to identify whether the V TH shift in our FETs results from changes in the density of charges or a variation of the V FB , we analyzed the mobility and the R c of the devices in the staggered configuration. Figure 6a shows the R c as a function of gate voltage measured using the transfer line method [38] for the reference device, and for the FETs containing 15 µm BV or 370 µm N-DMBI. The R c of the FET containing 370 µm N-DMBI shows a slight decrease to 1098 ohm·cm (at V G = 6 V) from the value of 1237 ohm·cm (at V G = 6 V) for the reference device.…”