Binary-Structured Si Surface Modification by an Alkaline Treatment: Application to Poly(3,4-Ethylenedioxythiophene)-Poly(Styrene Sulfonate)/Silicon Heterojunction Solar Cells

In recent years, silicon-organic hybrid solar cells have attracted tremendous research attention owing to their low production cost and high performance. In the present work, tapered silicon nanowires (TSiNWs) were synthesized on random micro-pyramids (RM pyramids). On this binary structure, a poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) polymer was spin-coated. The tapering of SiNWs was performed by immersing the samples in NaOH solution. It was found that the tapering time affects significantly the reflectivity, the minority carriers lifetime and the coverage rate of Si surface by the PEDOT:PSS film. Indeed, an optimal tapering time of 6 s was determined. This time was sufficient to good incident light trapping and to reduce the surface defects. This simple and low-cost surface structuring technique holds high potential for improving the performance of hybrid solar cells with large junction area.