Impact of Interface Recombination on Quantum Efficiency of a‐Si:H/c‐Si Solar Cells Based on Si Wires

Abstract

The impact of interface states on the quantum efficiency of a‐Si:H/c‐Si solar cells based on Si wires is studied using simulation and experimental measurements. The key role of the Si wire geometry for sensitivity of quantum efficiency to interface states on the sidewall is demonstrated. A decrease in Si wire diameter leads to enhanced recombination at the radial interface due to full inversion of the wire. Structures based on n‐Si wires with diameter of 0.5 and 1.5 μm and doping level of 2 × 1015 cm−3 fabricated using a combination of latex sphere lithography and cryogenic dry etching exhibit similar values of open‐circuit voltage (0.5 V) and strong differences for quantum efficiency spectra. For the structures based on Si wires with a radius (0.25 μm) smaller than the space‐charge region (0.6 μm) losses related to interface recombination leads to decrease in the quantum efficiency in the short‐wavelength region. The recombination losses may be reduced for Si wires with a radius exceeding the space charge region in silicon. In case of Si with a doping level of 1015–1016 cm−3, which is used for solar cells, the diameter of the wires should be above 1 μm.