Abstract
AbstractAlthough the density of states (DOS) distribution of charge transporting states in an organic semiconductor is vital for device operation, its experimental assessment is not at all straightforward. In this work, the technique of energy resolved–electrochemical impedance spectroscopy (ER‐EIS) is employed to determine the DOS distributions of valence (highest occupied molecular orbital (HOMO)) as well as electron (lowest unoccupied molecular orbital (LUMO)) states in several organic semiconductors in the form of neat and blended films. In all cases, the core of the inferred DOS distributions are Gaussians that sometimes carry low energy tails. A comparison of the HOMO and LUMO DOS of P3HT inferred from ER‐EIS and photoemission (PE) or inverse PE (IPE) spectroscopy indicates that the PE/IPE spectra are by a factor of 2–3 broader than the ER‐EIS spectra, implying that they overestimate the width of the distributions. A comparison of neat films of MeLPPP and SF‐PDI2 or PC(61)BM with corresponding blends reveals an increased width of the DOS in the blends. The results demonstrate that this technique does not only allow mapping the DOS distributions over five orders of magnitude and over a wide energy window of 7 eV, but can also delineate changes that occur upon blending.
Highlights
The density of states (DOS) distribution of charge transporting states consequence, charge transport in Organic semiconductors (OSs) is slowed down as compared to that in counin an organic semiconductor is vital for device operation, its experimental terpart perfect molecular crystals
A comparison of the HOMO and LUMO DOS of P3HT inferred from electrochemical impedance spectroscopy (ER-EIS) and photoemission (PE) or inverse PE (IPE) spectroscopy indicates that the PE/IPE spectra are by a factor of 2–3 broader than the ER-EIS spectra, implying that they overestimate the width of the distrisuch as the motion of a sheet of charge carriers injected from an electrode
Combined with PL spectroscopy we conclude that the simple point-site model, which rests upon the notion that disorder originates from of fluctuations of van der Waals coupling, is enough to understand disorder effects in PCBM
Summary
The density of states (DOS) distribution of charge transporting states consequence, charge transport in OSs is slowed down as compared to that in counin an organic semiconductor is vital for device operation, its experimental terpart perfect molecular crystals. It is well assessment is not at all straightforward. Characterization.[12,13] Disorder in OSs is manifested in the broadening of their absorption and photo luminescence spectra of OS-films It reflects (i) the local variation of the van der Waals coupling of a singlet or triplet state to the polarizable environment,[8]. For practical reasons they are amorphous tions are likely to change when going from neat to blended films
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