info:eu-repo/semantics/article
Determining the photoelectric parameters of an organic photoconductor by the photoelectromotive-force technique
Autor
SVETLANA MANSUROVA SERGUEYEVNA
Institución
Resumen
We report on a theoretical model to describe the non-steady-state photoelectromotive-force (photo-EMF)
effect in organic photoconductors. Unlike the conventional theory of the photo-EMF effect developed for
crystalline materials, this model accounts for the field dependence of the charge generation quantum efficiency
and charge carrier mobility. To verify our findings a detailed experimental study of the charge carrier generation
and transport processes in an organic photorefractive composite was performed using the photo-EMF effect
and ac photocurrent measurements. The investigated composite was based on a conjugated triphenyldiamine
based polymer (TPD-PPV) sensitized with a highly soluble fullerene derivative (PCBM). Our results show that
at zero and low dc field the dependence of the photo-EMF signal on frequency, grating period and external
electric field is well described by the standard model originally developed for an inorganic monopolar photoconductor
with finite charge carrier lifetime. In this regime the photo-EMF effect was used to determine zero and
low-field photoelectric material parameters including the low-field hole mobility (µ 0,h=1.3
X 10−4 cm2/V s), the effective charge carrier lifetime (ƭ=45 µ s), the diffusion length (LD=114 nm), and the
primary charge carrier generation efficiency (Φ=5.3 X 10−3%). In addition, the validity of the Einstein relation
(D/ µ =25 meV_ was verified for the low-field regime. At high electric fields the signal behavior deviates
significantly from the trend predicted by the standard model for inorganic photoconductors. This behavior
which is mainly attributed to the strong field dependence of the charge generation rate is well described by us
model.