Nanocrystalline silicon carrier collectors for silicon heterojunction solar cells and impact on low-temperature device characteristics
byGizem Nogay, Johannes Peter Seif, Yannick Riesen, Andrea Tomasi, Quentin Jeangros, Nicolas Wyrsch, Franz-Josef Haug, Stefaan De Wolf, Christophe Ballif
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.
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.