Benefit of Selective Emitters for p-Type Silicon Solar Cells With Passivated Surfaces

Abstract

We compare homogeneous and selective emitters on monocrystalline silicon solar cells with passivated surfaces and present an analysis of the saturation current densities influencing the open-circuit voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> and the fill factor FF . The cells' surfaces are passivated by a thin thermal oxide. Selective emitters are fabricated by laser doping from phosphosilicate glass. On both Czochralski-grown silicon (Cz-Si) as well as float zone silicon (FZ-Si), we find higher conversion efficiencies for the cells featuring a selective emitter. An efficiency up to 20.0% is reported on FZ-Si with an area of 148.4 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . For the selective emitter cells, 8 mV higher open-circuit voltages are found compared with the baseline. A saturation current analysis reveals that these cells exhibit a lower diode saturation current density of ideality 2 ( <i 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">02</sub> ), as well as improved shielding of the minorities in the emitter from the front contact. The selective emitter cells show a minor loss in short-circuit current density <i 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">SC</sub> of 0.5 % <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rel</sub> due to the presence of highly doped, illuminated areas. Front contact quality of the cells featuring a selective emitter is found to be superior compared with the cells with a homogeneously doped emitter.