Spin relaxation and structure of light-induced spin-correlated PCBM−/P3HT+ radical pairs

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

“…The latter is responsible for the distance and orientation distributions which lead to averaging out of the modulation pattern in ESEEM signals. In spite of these challenges, authors of [186][187][188][189] were able to detect after a laser flash the two-pulse out-of-phase ESE at X-band in both composites with PC 61 BM and PC 71 BM, confirming the spin-correlated nature of these CT-states. In the case of P3HT:PC 61 BM the characteristic time of the out-of-phase ESE decay with increasing delay after laser flash is 0.5 μs at 65 K, which gives a lower limit of the lifetime of these states.…”

“…Pulsed tr-EPR spectroscopy has also been employed to study the interfacial light-induced CT-states in P3HT:PC 61 BM and P3HT:PC 71 BM composites. [186][187][188][189] In general, time-resolved pulsed EPR spectroscopy is a powerful technique to study SCRP and has been widely used to characterize spin dynamics and geometry of SCRP in donor-acceptor systems at conventional, X-band and higher, Q-, W-, D-bands mw frequencies. [147,[174][175][190][191][192][193][194][195][196][197][198][199][200][201] Cw tr-EPR experiments are typically considerably more difficult at higher frequencies than X-band and have no yet been performed for BHJ systems.…”

Out-of-Phase Electron Spin Echo Studies of Light-Induced Charge-Transfer States in P3HT/PCBM Composite

“…They are subtracted when necessary to obtain the flash-induced ESE signal originating from the CT state. 19 For a smaller T DAF of 2.28 μs, the out-of-phase component of the ESE appears (Figure 1b). However, it has nearly symmetric positive and negative parts, which yields zero signal intensity upon integration in the time domain.…”

“…This rather crude approximation, however, reflects the delocalization of the P3HT + polaron on approximately 10 thiophene monomer subunits 36,37 and thus is more realistic than the point-dipole approximation used previously. 19 The point-dipole approximation is used for PCBM − since it is not expected to be significantly delocalized. The PCBM − point dipole is placed symmetrically at a distance r from the center of the P3HT + spin distribution.…”

“…18 To date, only in-phase ESE has been obtained for this system, which gives some estimation of the distance between the polarons in the CT state. 19 However, these experiments do not provide detailed data on the distribution of the distances between the radicals in the pair. Such information can be obtained from the out-of-phase ESE, a powerful tool to study SCRPs.…”