Simple Smoothing of the Bottom Silicon Surface Using Wet Chemical Etching Methods for Epitaxial III-V/Silicon Tandem Manufacturing

The implementation of diverse technologies has recently facilitated the production of cost-effective and highly efficient solar cells. High-efficiency solar cells with III-V compounds tandem crystalline silicon cells have achieved photovoltaic efficiency of higher than 39%. Etching silicon wafers plays a vital role in the deposition of epitaxial layers, neutralizing dangling bonds, and surface passivation for tandem solar cells. The wafers are polished using a solution of HF-HNO3-CH3COOH (HNA) and 20% KOH to smoothen the wafer surface. When HNA wet etching is performed for 3.5 min and the 20% KOH etching lasts for 6 min, the microroughness of the wafer is 1.9 nm with a measurement area of 10 x 10 mu m2 and 0.816 nm within an area of 1 x 1 mu m2. Compared with the as-cut wafer, the reflectance increases from 31.7% to 34.7%, and the effective minority carrier lifetime, with 30 nm Al2O3 passivation after 450 degrees C activated, increases from 1.4 to 1.8 ms in a carrier density of 1.0 x 1015 cm-3.