730 mV implied Voc enabled by tunnel oxide passivated contact with PECVD grown and crystallized n+ polycrystalline Si

Abstract

This paper presents the fabrication and optimization of tunnel oxide passivated contact with crystallized n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> polycrystalline Si (poly-Si) for high-efficiency large-area n-type front-junction Si solar cells. Starting with a baseline process, we optimized (a) the PECVD deposition precursor SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /PH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> flow rate, (b) the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas volume ratio, (c) the crystallization annealing temperature, (d) the tunnel oxide growth temperature, and (e) the deposition power to achieve the highest implied Voc. This resulted in an implied V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> of 730 mV, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ob</sub> ' of 4.3 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and implied fill factor (FF) of >84.5% with symmetric structure on n-type Cz substrate (~4 Ωcm, 170μm), indicating excellent interface passivation quality of tunnel oxide/n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> poly-Si contact. Applying a high dose ion-implanted boron emitter passivated with Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and screen-printed and fired Ag/Al front contact, 21.2% cell efficiency was achieved on 239 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> commercial grade n-type Cz wafers.