We discuss the measurement and analysis of current vs. voltage (I-V) characteristics of photovoltaic (PV) cells and
modules for reliability determination. We discuss both the error sources in the measurements and the strategies to
minimize their influence. These error sources include the sample area, spectral errors, temperature fluctuations, current
and voltage response time, contacting, and degradation during testing issues. Information that can be extracted from
light and dark I-V includes peak power, open-circuit voltage, short-circuit current, series and shunt resistance, diode
quality factor, dark current, and photo-current. The quantum efficiency provides information on photo-current
nonlinearities, current generation and recombination mechanisms.
We discuss the measurement and analysis of current vs. voltage (I-V) characteristics of organic and dye-sensitized
photovoltaic cells and modules. A brief discussion of the history of photovoltaic efficiency measurements and
procedures will be presented. We discuss both the error sources in the measurements and the strategies to minimize their
influence. These error sources include the sample area, spectral errors, temperature fluctuations, current and voltage
response time, contacting, and degradation during testing. Information that can be extracted from light and dark I-V
measurement includes peak power, open-circuit voltage, short-circuit current, series and shunt resistance, diode quality
factor, dark current, and photo-current. The quantum efficiency provides information on photo-current nonlinearities,
current generation, and recombination mechanisms.
Optimizing a concentrator system which uses multijunction solar cells is challenging because: (a) the conditions are
variable, so the solar cells rarely operate under optimal conditions and (b) the conditions are not controlled, so any
design problems are difficult to characterize. Any change in the spectral content of direct-beam sunlight as it passes
through the concentrator optics is of particular interest, as it can reduce the performance of multijunction cells and is
difficult to characterize. Here we show how the fill factor can be used to detect and diagnose this sort of a "spectral
skewing" by the concentrator optics during outdoor operation. The work presented here is for GaInP2/GaAs tandem
cells, but the conclusions are equally valid for GaInP2/GaAs/Ge triple-junction cells.
Photovoltaic power conversion efficiency is the single most important performance indicator. This paper gives an overview of procedures to determine the efficiency with respect to standard conditions. The measurement theory and general procedures for determining the efficiency with respect to reference conditions are well understood. The engineering challenge of commercial or custom equipment to perform accurate efficiency measurements for all photovoltaic technologies is discussed. Accurately measuring the performance of multijunction devices requires adjusting the intensity and spectral content of the light source so that each junction generates the proper photocurrent. Organic devices often have time constants on the photocurrent in excess of 1 s. This poses a variety of problems when measuring the quantum efficiency under 1-sun illumination or measuring the current-voltage characteristics. Many photovoltaic cells have reversible and irreversible transients in the current and/or voltage. Module acceptance testing and qualification procedures often assume that these transients are not present. The sample with the highest efficiency may not produce the highest energy because the photovoltaic performance is a function of the spectral content of the light, total irradiance, and temperature-all of which are different in the "real world" than under standard reference conditions.
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