Power loss calculation as a reliable methodology to assess the ohmic losses of the planar ohmic contacts formed on the photovoltaic devices |
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Authors: | P Narayanan Vinod |
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Affiliation: | (1) Naval Physical and Oceanographic Laboratory, Thrikkakara P.O., Cochin, 682 021, Kerala, India |
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Abstract: | The front grid contact is particularly important and requires a low contact resistance which represents the resistance associated
with the barrier at the interface of the metal and semiconductor contact structure. Often applied metal contacts are fired
at a higher temperature (typically above 700 °C) in air ambient, which produces ohmic contact on both surface of the photovoltaic
device. The specific contact resistance is one of the important device parameter on studying the interfacial properties of
the metalization system. Therefore, a reliable methodology to assess the ohmic losses of the applied metal contact structure
is required. It shows that it is rather simple and reliable to assess the electrical quality of the applied metal contacts
by quantifying the total ohmic losses of the solar cell associated with the various resistive components of the solar cell
normalized to unit cell area. It has been recently demonstrated that with a new experimental procedure, namely iteration method
based on the calculation of power loss (ICPL) associated with the contact resistance of the front Ag thick-film metal contacts,
a much reliable value of the specific contact resistance of the order of ≅10−5 Ω cm2 can be extracted for the planar ohmic contacts. In this work, the specific contact resistance of the planar ohmic contacts
formed on the heavily doped n+ region of the solar cells were studied on large number of finished cells by two independent methods: (i) standard three-point
probe (TPP) and (ii) iteration technique based on the calculation of the power loss (ICPL) associated with the contact resistance
of the front Ag contacts of the solar cell normalized to unit cell area. It shows that the value of specific contact resistance
measured by both methods are desirably much lower than the expected value of 10−3 Ω cm2 for the screen-printed Ag metal contacts of the photovoltaic cells used for the A.M. 1.5 applications. Using the iteration,
each resistive components of the solar cell normalized to unit cell area were directly evaluated. It is shown that by combining
the measurements of specific contact resistance of the planar ohmic contacts and ohmic losses of the cell, it gives a direct
and non-destructive diagnostic tool to qualitatively check the electrical quality of the applied Ag metal contacts.
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