Exciton diffusion in near-infrared absorbing solution-processed organic thin films

Abstract

We report on singlet-singlet annihilation and exciton diffusion in as-prepared p-type and annealed n-type thin films of the low-bandgap quinoidal quaterthiophene [QQT(CN)4] using ultrafast transient absorption measurements. The decay dynamics of exciton populations are well described by a one-dimensional diffusion-limited bimolecular recombination, indicating that the singlet excitons migrate preferentially along the stacking direction. Our results show that the exciton diffusion constants in QQT(CN)4 films do not vary significantly upon thermal annealing. Exciton diffusion lengths are measured to be as high as 4 and 5 nm in as-prepared and annealed QQT(CN)4 films, respectively. We also observe an influence of the excitation densities on the singlet exciton diffusion, which is attributed to phonon scattering. Because of the possibility of patterning p-n regions in QQT(CN)4 films by thermal nanolithography techniques, this study provides important insight not only into the photophysical properties of quinoidal oligothiophene derivatives but also for their future integration into high-performance p-n nanostructured near infrared light-sensing devices.

Ground- and excited-state characteristics in photovoltaic polymer N2200

“…43,44 In conjugated polymers, exciton-exciton annihilation can be employed to estimate the diffusion length of singlet exciton. 26,44,[48][49][50][51] The singlet exciton dynamics can be described as 44 dnðtÞ dt ¼ ÀknðtÞ À gn 2 ðtÞ (1)…”

“…24,25 To realize high exciton dissociation efficiency, the excitons must diffuse and reach the interface within its lifetime. 26 Therefore, exciton diffusion length of neat polymer is an essential parameter for high-efficient organic photovoltaics materials and devices. Moreover, exciton diffusion characteristics are closely related to the excited-state properties of organic semiconductor materials.…”

The Active Layer Morphology of Organic Solar Cells Probed with Grazing Incidence Scattering Techniques

“…However, due to the short lifetime of the strongly bound exciton, a very limited diffusion length of the excitons is a key signature of OPV devices. Typical reported exciton diffusion lengths are in the order of 10 nm . As a consequence, not only the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the donor and acceptor material but also the local morphology of the donor‐acceptor interface will have a strong influence on the overall device performance.…”

Exciton dynamics in two-dimensional MoS2 on a hyperbolic metamaterial-based nanophotonic platform

“…To better understand the diffusion mechanism, we plot D versus the inverse of square root of the pump fluence that corresponds to the inverse square root of temperature (T −1/2 ) in SI- Figure 9. The linear behaviour of D with T −1/2 indicates that the diffusion process takes place through phonon scattering 43,44 .…”