Reduction of sunlight reflection on surfaces of solar cells by fabricating hexagonal lattices in multicrystalline silicon

Abstract

A new method for reducing surface reflectance of multicrystalline silicon wafers is presented. The method using holographic lithography and wet etching to fabricate 2-dimensional (2D) photonic crystal (PC) on the surface of multicrystalline silicon. 2D hexangonal PC structures with micron scale lattice constant exhibit significant reduction of the surface reflectance. In the method, 2D hexagonal PC structure is firstly recorded in photoresist, which is coated on the surface of Si wafer, using holographic 3-beam interference technique. After exposure and development the wafer is put into acid solution to transfer the lattice structure into the silicon. Experiments with different exposure angles and etching times were carried out to form different lattice period and structure depth for obtaining optimal lattice parameters. PC with 1.3 μm lattice constant and 0.5 μm depth has achieved a reflectance below 6%. The holographic technique used in the work allows large-area lattice fabrication with only one process. The proposed method has the advantages of low production cost and high throughput, enabling industrial mass production of Si solar cells.