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–HNO 3 –CH 3 COOH (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 × 10 μm 2 and 0.816 nm within an area of 1 × 1 μm 2 . Compared with the as‐cut wafer, the reflectance increases from 31.7% to 34.7%, and the effective minority carrier lifetime, with 30 nm Al 2 O 3 passivation after 450 °C activated, increases from 1.4 to 1.8 ms in a carrier density of 1.0 × 10 15 cm −3 .