Nanocrystalline silicon carrier collectors for silicon heterojunction solar cells and impact on low-temperature device characteristics

by Gizem Nogay, Johannes Peter Seif, Yannick Riesen, Andrea Tomasi, Quentin Jeangros, Nicolas Wyrsch, Franz-Josef Haug, Stefaan De Wolf, Christophe Ballif
Year: 2016

Bibliography

Nogay, Gizem, Johannes Peter Seif, Yannick Riesen, Andrea Tomasi, Quentin Jeangros, Nicolas Wyrsch, Franz-Josef Haug, Stefaan De Wolf, and Christophe Ballif. "Nanocrystalline silicon carrier collectors for silicon heterojunction solar cells and impact on low-temperature device characteristics." IEEE Journal of Photovoltaics 6, no. 6 (2016): 1654-1662.

Abstract

​Silicon heterojunction solar cells typically use stacks of hydrogenated intrinsic/doped amorphous silicon layers as carrier selective contacts. However, the use of these layers may cause parasitic optical absorption losses and moderate fill factor (FF) values due to a high contact resistivity. In this study, we show that the replacement of doped amorphous silicon with nanocrystalline silicon is beneficial for device performance. Optically, we observe an improved short-circuit current density when these layers are applied to the front side of the device. Electrically, we observe a lower contact resistivity, as well as higher FF. Importantly, our cell parameter analysis, performed in a temperature range from -100 to +80 °C, reveals that the use of hole-collecting p-type nanocrystalline layer suppresses the carrier transport barrier, maintaining FF s in the range of 70% at -100 °C, whereas it drops to 40% for standard amorphous doped layers. The same analysis also reveals a saturation onset of the open-circuit voltage at -100 °C using doped nanocrystalline layers, compared with saturation onset at -60 °C for doped amorphous layers. These findings hint at a reduced importance of the parasitic Schottky barrier at the interface between the transparent electrodes and the selective contact in the case of nanocrystalline layer implementation.

Keywords

transport contact resistivity nanocrystalline silicon Schottky barrier silicon heterojunction (SHJ) Solar cells temperature dependence