Influence of Intrinsic Silicon Layer and Intermediate Silicon Oxide Layer on the Performance of Inline PECVD Deposited Boron-Doped TOPCon

Abstract

In this article, the development and optimization of carrier-selective and passivating contacts by industry-scale inline plasma-enhanced chemical vapor deposition and their successful integration into solar cells are reported. Amorphous Si thin films with varying carbon content (SiC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) were deposited on a thermally grown ultrathin tunnel oxide (TOPCon) and electrically characterized. Furthermore, the impact of a vacuum break (VB) during the deposition of a layer stack consisting of intrinsic amorphous Si [a-Si:H(i)] and boron-doped SiC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> was investigated. That is, samples that were processed with VB were exposed to ambient air, and hence, a thin native oxide was formed on the a-Si:H(i) layer, which affected the boron diffusion into the absorber resulting in a distinct anneal behavior of the contacts. Upon optimization, these layers provided an excellent surface passivation quality, which was reflected in an implied open-circuit voltage of 733 mV for n-type and 716 mV for p-type TOPCon structures, respectively. In addition, very low contact resistivities of 0.3 mΩ-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for n-type and 0.5 mΩ-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for p-type TOPCon were measured, respectively. These optimized TOPCon structures were implemented into both sides contacted p-type laboratory solar cells. After a two-step furnace anneal, these cells achieved a maximum energy conversion efficiency of 22.7% with evaporated contacts.