Influence of the Dopant Gas Precursor in P-Type Nanocrystalline Silicon Layers on the Performance of Front Junction Heterojunction Solar Cells
Luca Antognini, Vincent Paratte, Jan Haschke, Jean Cattin, Julie Dréon, Mario Lehmann, Laurie‐Lou Senaud, Quentin Jeangros, Christophe Ballif, Mathieu Boccard
Abstract
Silicon heterojunction solar cells can employ p-type hydrogenated nanocrystalline silicon nc-Si:H(p) on their front side, since these can provide better transparency and contact resistance compared to hydrogenated p-type amorphous silicon layers. We investigate here the influence of trimethyl boron (TMB) and BF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as dopant source on the layer properties and its performance in solar cells. Both gases enable high efficiencies but yield a different crystallinity and effective doping. A high BF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> flow lowers the series resistance through a low activation energy of dark lateral conductivity and maintains a high crystallinity. This allows fill factors up to 83%, however with the apparition of a parasitic absorption in the UV. A low TMB flow enables simultaneously a high crystallinity and a low activation energy. As an illustration of this layer potential, a 23.9%-certified efficiency is achieved with a 2 × 2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> screen-printed device. We finally suggest that similar transport versus transparency trade-offs can be reached for both dopant types for front junction application, while high BF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> flow allowing lower series resistance might be of interest when placed on the rear side.