How to Find Out the Density of States in Disordered Organic Semiconductors

Abstract

We suggest a recipe on how to determine the density of states (DOS) in disordered organic semiconductors from the measured dependence of the charge carrier mobility on the concentration of carriers n. The recipe is based on a theory for the concentration-dependent mobility. As an example, we apply our theoretical results to experimental data obtained on two polymers and show that from the class of trial DOS functions g(ε)∝exp{-(ε/σ)(p)}, only those with p>1.8 can explain the experimental results. In particular, we claim that the concentration-independent mobility at low n evidences that the DOS cannot be purely exponential, which is in contrast to numerous recent assumptions in the literature.

Energy resolved electrochemical impedance spectroscopy for electronic structure mapping in organic semiconductors

“…(1)) and its consequent independence of the results for any transport quantity, e.g., the mobility and its dependence on the applied field; 16 (ii) the ability to control shifts in the semiconductor Fermi level position using the external voltage U, provided that the voltage shift of the electrolyte chemical potential is neglected (this is justified by the electrolyte's much larger DOS value); and (iii) the linearity of the electrochemical systems, 1 which enable application of the perturbation method.…”

“…17 This DOS spectrum implies hopping charge transport via the Gaussian distributed localized states to be the predominant transport path. 16,18 There is also an absence of deep traps in the band gap between the HOMO and LUMO, where the DOS is 4-5 orders of magnitude lower than the DOS of the transport paths. Figure 2 also shows that the absence of filtering and bubbling of the PMPSi solution and spin-coating and drying in the air all introduce extra defect states into the band gap.…”

Consistent formulation of the crossover from density to velocity dependent recombination in organic solar cells

“…For the Gaussian DOS, most relevant to organic blends, E tr lies around the center of the Gaussian, the acceptor lowest-unoccupied molecular orbital (LUMO). 22,23 Average probability of the recombination at each step of the hopping can then be expressed as…”

“…Using the method used in Ref. 23 to calculate these average quantities and by straightforward algebraic manipulation, we finally get a general expression for the recombination rate as follows:…”

Estudo atomístico da desordem eletrônica em filmes amorfos de polímeros conjugados

“…O modelo de desordem gaussiana leva a resultados adequados na parametrização das curvas experimentais de mobilidade de buracos [33,34,35,36], sendo amplamente empregado apesar de contestado por outros estudos. Por exemplo, simulação de P3HT em modelos de alta desordem utilizando uma aproximação baseada em resultados da Teoria do Funcional da Densidade (DFT) [37,38] leva a uma forma exponencial para a DOS.…”