Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Abstract

Using electrically and capacitively detected magnetic resonance (EDMR and CDMR) techniques, we clarified recombination in regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) films, which is an important elementary process for photoconduction. The modulation frequency dependences of the EDMR and CDMR reveal the coexistence of two types of electron− hole (e−h) pairs with different lifetimes in the device fabricated with a Schottky contact between P3HT and an Al electrode. The short-lived e−h pair is a precursor of the recombination of free carriers in the bulk P3HT. The long-lived e−h pair is involved in the recombination of space charges in the Schottky junction region, which leads to an enhancement of the photocurrent.

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

“…The observed f AM dependence of the EDMR is well fitted by a sigmoid function of with Δ I 0 = −29 pA and τ = 13 μs. This τ value agrees with that estimated from the modulation frequency dependence of the 179 MHz EDMR signal of a P3HT film . Under the steady-state approximation of the e–h pair in Scheme , the value of τ is equal to the carrier recombination time, as expressed by Here, k f , n̅ c , and ϕ rec represent the rate constant for the formation of an e–h pair, the number density of the free carriers, and the recombination yield, respectively (see Section S5 for further details).…”

“…The negative phase of the Zeeman resonances can be explained by an increase in recombination yield of the e−h pair with preferential singlet recombination. 22 However, the origin of the zero-field signal differs from that of the Zeeman resonance. The difference between the zero-field signal and the Zeeman resonance is supported by an observed RF power dependence; the intensity of the zero-field signal is more sensitive than the Zeeman resonances to the P 50Ω (Figure S3).…”

“…This τ value agrees with that estimated from the modulation frequency dependence of the 179 MHz EDMR signal of a P3HT film. 22 Under the steadystate approximation of the e−h pair in Scheme 1, the value of τ is equal to the carrier recombination time, as expressed by…”

“…The observed angle dependence indicates that the signals at ±0.36 mT can be assigned to the ESR of Zeeman sublevels of the e–h pair, referred to as the Zeeman resonance. The negative phase of the Zeeman resonances can be explained by an increase in recombination yield of the e–h pair with preferential singlet recombination . However, the origin of the zero-field signal differs from that of the Zeeman resonance.…”

Probing an Isolated Conjugated Polymer Molecule with Radiation-Generated Spin-Correlated Polaron Pairs

“…The isotropic value of the g -factor, ( g xx + g yy + g zz )/3, for the P3HT-rra negative polarons is approximately 2.0035. This value is lower than the value of 2.0045 observed for these particles in solution but falls within the range of values of 2.0031–2.0044 obtained by EPR spectroscopy of the solid phase in steady-state experiments. − The scatter between the observed average g -values may be attributed to differences between the conformations of P3HT molecules that lead to a different partial averaging of the g -tensor anisotropy during migration of a negative polaron along the polymer chain. This result implies that in this regard, the polaron migration along a P3HT-rra molecule isolated in the PVC matrix does not differ substantially from the migration in pristine P3HT-rra.…”