New Schottky-Type Wire-Based Solar Cell with NiSi_x Nanowire Contacts

Solar cells built with arrays of semiconductor wires have been studied for several years. They present some potential advantages over their bulk counterparts, such as (much) less use of semiconductor material, as well as improved light absorption properties. Most wire-based solar cells are fabricated with arrays of semiconductor p–n junctions, either radial or axial. Here, using a newly developed random connection process based on nickel silicide nanowires, we have built Schottky-type solar cells on interdigitated base and emitter coplanar electrodes that reach an efficiency of 6.5% when only 64% of the footprint area of the device is covered with p-type Si wire light-absorbers. To the best of our knowledge, this is the best efficiency reported so far for a Schottky-type wire-based solar cell; a simple extrapolation of the surface area suggests that an efficiency of more than 10% can be reached, which is comparable to that of single-junction hydrogenated amorphous Si cells. We also compare the Schottky-type cell with a “control” p–i–n one using the same device layout and the same nickel silicide nanowire random connection process: the efficiency of the p–i–n cell is higher (∼8%) but this is due to a higher VOC, the short-circuit current density (ISC) being very similar in both cases, close to 20 mA/cm2. The maximum temperature reached throughout the fabrication process of the cells (whether Schottky-type or p–i–n) is 550 °C, corresponding to the growth of the crystalline Si wires. Altogether, the results presented here hold promises toward cheap photovoltaics based on the use of randomly organized and randomly connected Si wire arrays.