Exciton–exciton annihilation and relaxation pathways in semiconducting carbon nanotubes

Abstract

We present a thorough analysis of one- and two-color transient absorption measurements performed on single- and double-walled semiconducting carbon nanotubes. By combining the currently existing models describing exciton-exciton annihilation-the coherent and the diffusion-limited ones-we are able to simultaneously reproduce excitation kinetics following both E11 and E22 pump conditions. Our simulations revealed the fundamental photophysical behavior of one-dimensional coherent excitons and non-trivial excitation relaxation pathways. In particular, we found that after non-linear annihilation a doubly-excited exciton relaxes directly to its E11 state bypassing the intermediate E22 manifold, so that after excitation resonant with the E11 transition, the E22 state remains unpopulated. A quantitative explanation for the observed much faster excitation kinetics probed at E22 manifold, comparing to those probed at the E11 band, is also provided.

Photoinduced electron transfer processes of single-wall carbon nanotube (SWCNT)–based hybrids

“…Global analysis of the transient decay dynamics reveals four time constants (Figure 7d): 0.6 ps (62%), 16.3 ps (30%), 408 ps (8%) and a fourth one that exceeds the limitation (>3 ns) of the instrument coverage. The processes observed at 0.6 and 16.3 ps were assigned to the exciton-exciton annihilation and singlet exciton recombination [63,[68][69][70]. However, the long-lived component (408 ps) was not observed previously.…”

High Conversion Efficiency Carbon Nanotube-Based Barrier-Free Bipolar-Diode Photodetector

“…To estimate the width ( L eff ) of these high field regions, we assume that S Pd and S Sc are of the same width, and we employ a time-resolved and spatial-resolved Monte Carlo simulation to model the excitons’ dynamic behaviors in BFBD devices. We integrate the excitons dissociation over time and space to obtain the conversion efficiency (η): − where G i is the generating function of the excitation pulse for the E ii photoexcitation and i = 1,2. Details on the simulation are given in the Supporting Information.…”

“…Careful examination of Figure c,d reveals that η 11 is slightly larger than 2 L eff / L ch . This suggests that only a few excitons initially generated outside the high field regions ( S Pd and S Sc ) may diffuse into the these regions and contribute to photocurrent before disappearing via such effective processes as exciton–exciton annihilation and recombination in the low-field region. − For E 22 excitons, the decay rate ( k 21 –1 ) from E 22 state to E 11 state is estimated to be k 21 –1 ∼ 0.5 ps. This value is consistent with results measured in femtosecond transient absorption spectroscopic studies. − , This is the reason why η 22 is generally lower than η 11 in the same device because of the nonradiatively decay of E 22 excitons by Auger recombination in the effective region …”

“…This value is consistent with results measured in femtosecond transient absorption spectroscopic studies. [34][35][36]38…”

Electronic energy pooling in organic systems: a cross-disciplinary tutorial review

“…As a result, the rates of exciton annihilation observed in both crystalline and amorphous solids and in polymer blends will often need to be measured for each set of reproducibly-synthesized samples. For solids, some simplicity can sometimes be achieved by employing 1-dimensional active components such as carbon-nanotubes, 105 or inert 3dimensional frameworks such as MOFs 102,106 into which the active components can be dispersed with geometric order.…”