The thermal behaviour of mass production terrestrial solar modules is a somehow neglected
but very important issue of photovoltaics. Despite its significant influence on the
power generation, the thermal properties of solar modules are mostly not taken into
account in daily applications. In recent literature thermal transient testing was
suggested as a possible solution to proper thermal characterization of photovoltaic
devices. In this paper we give a short overview on the known issues of the thermal
transient testing of photovoltaic devices and address the issue of the variation of
the structure function at different heating currents as well as the influence of the
initial degradation of amorphous solar cells on the measurement results. It is shown
that for small current densities the increasing forward driving current (i.e. the
heating current) can have a strong influence on the size of the active area that on
the other hand determines the volume of the heat path. Due to this an increasing heating
current results in the decrease of the junction to ambient thermal resistance, with
the thermal resistance converging to a minimum value at high heating currents. The
phenomenon was also investigated by Kelvin probe potential mapping. In addition it
was investigated how the initial degradation of amorphous silicon solar cells effect
the results of the thermal transient measurement.
