Abstract
Light beam induced current (LBIC) measurements of
ITO-free organic photovoltaic modules with monolithic
series connection are presented. Selective bias
illumination is used to extract the light beam generated
current from the module. A large variation of the
photocurrent is observed among the cells which is
unlikely to match the real generated photocurrent. In
order to investigate this behavior, a novel approach
(filtering approach) is presented in which the
photocurrent of the measured cell is reduced while the
remaining cells are kept under full illumination. This
method enables the detection of the correct photocurrent
of each cell and thus to identify the cell which limits
the module current if all the cells comprise large
parallel resistances. Dark lock-in thermography
measurements of the module revealed several shunted
cells. In this case the filtering approach overestimates
the photocurrent. Numerical simulations of LBIC applied
to modules using either selective bias illumination or
forward bias voltage were carried out to understand the
observed behavior in detail. The results reveal that a
reliable detection of the photocurrent is impossible when
several cells have rather low parallel resistances.
Whereas for selective bias illumination the photocurrent
response of the measured cell is an unambiguous function
of the cell?s parallel resistance this is not the case
for an applied forward bias voltage.
Original language | English |
---|---|
Pages (from-to) | 157-164 |
Journal | Solar Energy Materials and Solar Cells |
Volume | 134 |
DOIs | |
Publication status | Published - 2015 |
MoE publication type | A1 Journal article-refereed |
Keywords
- Organic solar cells
- Imaging of modules
- Photocurrent imaging
- LBIC
- DLIT
- Parallel resistance
- Shunts