UV-Ozone Oxide for Surface Clean, Passivation, and Tunneling Contact Applications of Silicon Solar Cells

Abstract

We demonstrate the versatile use of UV-ozone oxide (UVo) in surface cleaning, surface passivation, diffused junction passivation, and current tunneling applications of crystalline silicon (c-Si) solar cells. A UV-ozone generated oxide is used as a surface clean for random textured c-Si samples and the effectiveness of surface clean is determined by capping with a thin layer of aluminum oxide (AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ). Our developed UVo clean has resulted in a cleaning efficiency almost comparable to that of the benchmarked RCA clean, yielding a saturation current density of 12 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . When planar and textured c-Si samples are capped by a stack of UVo and AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , a UV-ozone growth time of no more than 3 min is found to provide an optimum surface passivation. When tested on phosphorus and boron diffused junctions (with sheet resistance, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sh</sub> of 110–120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega\!/\!{\scriptstyle\square} $</tex-math></inline-formula> ), the UVo and AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> stack resulted in a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> of 11 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or lower. The high-resolution transmission electron microscope imaging revealed that UVo structure is stable upon annealing for passivation activation. Last, when applied as a tunneling contact, the UVo realizes a contact resistivity ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ρ_c</i> ) of ∼1 mΩ-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and ∼20 mΩ-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for boron and phosphorus doped metal-insulator-semiconductor contact structures, respectively, with moderately doped diffusions.