Photogenerated carrier dynamics of TIPS-pentacene films as studied by photocurrent and electrically detected magnetic resonance

Abstract

The carrier generation process and spin dynamics through photoexcitation in the vacuum vapour deposition film of TIPS-pentacene were investigated by temperature dependence measurements of photocurrent and electrically detected magnetic resonance.

Readout of Oriented Triplet Excitons in Linear Acenes via Room-Temperature Electrically Detected Magnetic Resonance

“…The distinct orientation is evident when compared to the simulated powder spectrum, whereby the triplet contributions from different molecular orientations result in a significantly broadened centralized component. The fact that the neat acene spectra reveal no triplet features while undergoing strong SF is counterintuitive, but this is consistent with previous studies. ,,,, The neat acene films measured through EDMR produce only one center-field peak that fits well to a sum of Gaussian and Lorentzian line shapes, shown in the cryogenic EDMR section of the Supporting Information This center-field peak is commonly attributed not to the high triplet density from the SF process, but to mobile and trapped charges that undergo a symmetric spin flip, placing them directly at the center-field of the chosen resonant frequency. Here the 9.625 GHz frequency corresponds to a g = 2 center-field line of 344.1 mT.…”

“…Delocalization of excitonic species varies dramatically based on material, with some polymeric species exhibiting exciton delocalization upward of 50 nm, while most organics host an exciton on just one or two molecules. ,− Triplet exciton species tend to be more tightly bound and more localized than their singlet counterparts, and in the linear acenes tend to be constrained to one molecule at most. ,,,, In high concentration, neighboring molecules would tend to delocalize more, resulting in triplet transitions that are less constrained to the molecular axes and an overall reduction in the effective zero field splitting. On the other hand, spin–lattice relaxation effects are caused primarily via exciton hopping in the high concentration limit. , Triplet excitons are significantly less mobile than singlets in the linear acenes, but are still able to travel long distances due to considerable lifetimes. ,,− In the dilute regime, excitons would tend to be isolated and trapped, drastically reducing the spin–lattice relaxation and increasing the initial polarization caused by SF.…”

“…As seen at the top of Figure , not all magnetic resonance techniques have been able to observe triplet sublevel transitions within the series. Anthracene is well-studied and displays strong triplet and doublet features via Electrically Detected Magnetic Resonance (EDMR), but similar studies of Tc and Pc reveal only doublet features. ,− The Optically Detected Magnetic Resonance (ODMR) scheme measures the change in optical emission or absorption of a specific state under resonant conditions, and has been used to observe oriented triplet features in Tc. , Electron Paramagnetic Resonance Spectroscopy (EPR) typically involves modulation of the applied field and measures the resulting change in reflected microwave intensity. , EPR experiments are often conducted with dilute solid state samples under cryogenic conditions to limit spin–lattice relaxation effects, and have successfully revealed triplet features in all three acenes. ,,, …”

Radiowave Effects on an Electron–Hole Pair in a Poly(3-hexylthiophene) near Zero Magnetic Field

“…The lifetime of the e–h pair in P3HT was determined to be 20–30 ns estimated by 4/( k S + 4 k d ), based on the average lifetime of singlet and triplet e-h pairs . This lifetime is similar to those of the e–h pairs generated in solid organic materials, as determined using the magnetophotoconductance and conventional EDMR measurements. − …”

Decoding eumelanin's spin label signature: a comprehensive EPR analysis

“…(vi) Electrically detected magnetic resonance (EDMR): [154][155][156][157] this magnetic resonance spectroscopy can provide information on free radicals' electronic and magnetic properties by measuring the spin-dependent transport of charge carriers under the influence of a magnetic field. Compared to conventional EPR, EDMR is extremely sensitive, down to 100 spins (at liquid helium temperatures).…”