Study the Effect of Silicon Nanowire Length on Characteristics of Silicon Nanowire Based Solar Cells by Using Impedance Spectroscopy

Silicon nanowire (SiNW) arrays were produced by electroless method on polycrystalline Si substrate, in HF/AgNO3 solution. Although the monocrystalline silicon wafer is commonly utilized as a perfect substrate, polycrystalline silicon as a low cost substrate was used in this work for photovoltaic applications. In order to study the influence of etching time (which affects the SiNWs length) on different elements in AC equivalent circuit of the fabricated solar cells, impedance spectroscopy was accomplished for the first time in forward bias direction and under illumination. Measurements indicated a growth of recombination with increase in etching time that may be attributed to enhancement in the number of defects on nanowires surfaces as a result of increase in the length of SiNWs. This trend reduces recombination resistance in device equivalent AC circuit and reduces the efficiency of solar cells. Impedance spectra and fitting curves also showed that the effective carrier lifetime decreases with increase in etching time.