Effective way to realize optimized carrier recombination and electrode contact for excellent electrical performance silicon nanostructure based solar cells

Abstract

Silicon nanostructures promise to reduce light loss and increase the power conversion efficiency of photovoltaic devices. So far, however, solar cells based on nanostructured silicon exhibit lower power conversion efficiency than conventional solar cells due to the enhanced surface recombination associated with the nanostructures and poor front electrode contact. Here, we report a simple and effective way to modify silicon nanostructures grown on pyramid-structure surface by using ammonium hydroxide (NH4OH) and hydrogen peroxide (H2O2) solution. Through the process, silicon nanostructures are etched off at the peaks of pyramid-structures, thus the coverage rate of nanostructures on pyramids declines to 0.3. The surface modification dramatically suppresses the carrier recombination and the effective minority carrier lifetime is improved from 10.1 to 26.0 μs, thus the resulted open current circuit voltage (Voc) increases from 595 to 602 mV. The decrease of coverage rate of nanostructures reduces contact area between metal electrodes and nanostructured surface and the front electrode contact improves, thus the contact resistivity declines from 4.107 × 10−4 to 7.805 × 10−5 Ω/cm2 and series resistance declines from 0.63 to 0.46 Ω. Although the average reflectance in the visible spectrum region increases about 2 % after the treatment, combining of these aspects, the reformed solar cells show higher conversion efficiency than conventional nanostructured silicon solar cells.