Page 104 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
P. 104
Chapter 3
(V ), fill factor (FF), as well as the series (R ) and the shunt (R ) resistances were directly
oc
sh
s
determined from the current voltage curve. Since the PI samples did gave unstable
measurements at negative voltages, the determination of the shunt resistance
should be treated with care and is only included at temperatures below 80C. It
o
should be noted that the setup cannot execute External Quantum Efficiency (EQE)
measurements, so the current density is indicative and can be used for comparison
as a function of time, but not as absolute value. However, before degradation, the
current density values obtained from EQE and the setup are mostly close.
Furthermore, a fitting procedure based on the single diode model is used to calculate
the photogenerated current density (J), ideality factor (n), saturation current
ph
density (J ) and series and shunt resistance. The fitting procedure consists of an
o
estimation of every parameter, obtained by simplifying and manipulating equation
(3.5), as described in reference [5]. An algorithm was used in order to find the best
combination of parameters fitting the IV-curve, starting from the estimation fed to
the fitting program. It should be noted that regardless of these precautions, fitting of
the IV curve can result in unreliable results and depends on the estimations on which
the first fits are based. In this study, we judged that the fitting resulted in reasonably
reliable values for non-degraded samples on soda lime glass, but becomes less
trustworthy when the solar cell is degraded and its electrical behaviour differs
strongly from an ideal diode. Therefore, the validity of all data is still under discussion
and data of degraded cells is not shown in this thesis.
Figure 3.9
Photograph of the commercial hybrid degradation setup.
102
(V ), fill factor (FF), as well as the series (R ) and the shunt (R ) resistances were directly
oc
sh
s
determined from the current voltage curve. Since the PI samples did gave unstable
measurements at negative voltages, the determination of the shunt resistance
should be treated with care and is only included at temperatures below 80C. It
o
should be noted that the setup cannot execute External Quantum Efficiency (EQE)
measurements, so the current density is indicative and can be used for comparison
as a function of time, but not as absolute value. However, before degradation, the
current density values obtained from EQE and the setup are mostly close.
Furthermore, a fitting procedure based on the single diode model is used to calculate
the photogenerated current density (J), ideality factor (n), saturation current
ph
density (J ) and series and shunt resistance. The fitting procedure consists of an
o
estimation of every parameter, obtained by simplifying and manipulating equation
(3.5), as described in reference [5]. An algorithm was used in order to find the best
combination of parameters fitting the IV-curve, starting from the estimation fed to
the fitting program. It should be noted that regardless of these precautions, fitting of
the IV curve can result in unreliable results and depends on the estimations on which
the first fits are based. In this study, we judged that the fitting resulted in reasonably
reliable values for non-degraded samples on soda lime glass, but becomes less
trustworthy when the solar cell is degraded and its electrical behaviour differs
strongly from an ideal diode. Therefore, the validity of all data is still under discussion
and data of degraded cells is not shown in this thesis.
Figure 3.9
Photograph of the commercial hybrid degradation setup.
102
