Laa. Pettersson et al., Modeling photocurrent action spectra of photovoltaic devices based on organic thin films, J APPL PHYS, 86(1), 1999, pp. 487-496
We have modeled experimental short-circuit photocurrent action spectra of p
oly(3-(4'-(1 ",4 ",7 "-trioxaoctyl)phenyl)thiophene) (PEOPT)/fullerene (C-6
0) thin film heterojunction photovoltaic devices. Modeling was based on the
assumption that the photocurrent generation process is the result of the c
reation and diffusion of photogenerated species (excitons), which are disso
ciated by charge transfer at the PEOPT/C-60 interface. The internal optical
electric field distribution inside the devices was calculated with the use
of complex indices of refraction and layer thickness of the materials as d
etermined by spectroscopic ellipsometry. Contributions to the photocurrent
from optical absorption in polymer and fullerene layers were both necessary
to model the experimental photocurrent action spectra. We obtained values
for the exciton diffusion range of 4.7 and 7.7 nm for PEOPT and C-60, respe
ctively. The calculated internal optical electric field distribution and re
sulting photocurrent action spectra were used in order to study the influen
ce of the geometrical structure with respect to the efficiency of the thin
film devices. In this way the photocurrent was optimized. (C) 1999 American
Institute of Physics. [S0021-8979(99)05113-0].