Characterization of Laser-Doped Localized p-n Junctions for High Efficiency Silicon Solar Cells

Abstract

To further increase the efficiency of industrial crystalline silicon solar cells, a point-contact solar cell concept with localized p-n junctions is considered a promising candidate if implemented by a low cost processing technique like laser doping. For efficient development and optimization of such a processing technique, we present a dedicated test structure to derive the fundamental diode characteristics specific to the localized p-n junction, namely the contact resistance to the metal and the recombination properties, i.e., the dark saturation current. Those properties are fitted to measured dark current-voltage curves by 3-D device simulations using Quokka. We show that in particular, the contact resistance can be accurately extracted and that the method is robust against uncertainties of other device properties of the test structure. Simulations of an idealized point-contact solar cell are performed to judge the usefulness of the extractable value range with respect to the efficiency potential. Furthermore, we apply the method to laser doping experiments. We successfully characterize the recombination and contact resistance and identify a ~24% efficiency potential of a nonoptimized two-step laser doping process. Other single step processes show a very high recombination (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0pn</sub> ≫ 1e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) likely due to imperfections around the perimeter of the laser processed area.