Local Thermographic Efficiency Analysis of Multicrystalline and Cast-Mono Silicon Solar Cells

Abstract

Local dark current contributions of multicrystalline (mc) and cast-mono silicon (Si) solar cells were evaluated by using dark lock-in thermography (DLIT) measurements. The goal of these investigations was to evaluate the influence of the contact metallization on the efficiency. Both materials are treated by nearly the same solar cell process. Because of a special print design, the current density caused by the front-side and rear-side silver metallization can be measured separately, and their influence on the overall cell performance can be estimated. We measure an increase of the local saturation current density <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J_{\bf 01}$</tex> </formula> by about 2.8 × 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-12}$</tex></formula> to 6.7 × 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-12}$</tex></formula> A/cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{2}$</tex></formula> at the soldering pads of the solar cell, compared with about 6 × 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-13}$ </tex></formula> A/cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{2}$</tex></formula> in the undisturbed regions. In the region of the front-side busbars, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J_{01}$</tex></formula> increases locally by about 4.5 × 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-13}$</tex></formula> to 17.6 × 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{-13}$</tex></formula> A/cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{2}$</tex></formula> . The local depletion region recombination current, as well as the ohmic shunt current, is not affected by the screen-printed contacts. The bulk and back surface recombination in mc-Si within regions with a low amount of defects are almost the same as in cast-mono material. However, in regions of recombination active bulk defects, a significant increase in the recombination activity at the front contact was observed.