Multijunction a-Si:H/c-Si solar cells with vertically-aligned architecture based on silicon nanowires

Abstract

The new design for full silicon multi-junction solar cells, which consists of combination of silicon nanowires (SiNWs) and conventional silicon-based hetero-junctions, is proposed in the paper. A top junction is based on SiNWs covered by a-Si:H p-i-n structures while bottom junction is based on amorphous/crystalline silicon (a-Si:H/c-Si) hetero-junctions. Vertically-aligned design of top p-i-n junction is a way to enhance absorption in a-Si:H without rising its thickness and therefore it allows one to increase short circuit current. This is a key issue for current match with bottom a-Si:H/c-Si heterojunction. Silicon wires of submicron diameters and micron length are formed by etching. A cost effective technology to form the periodic SiNWs on the silicon front surface was developed based on dry plasma etching using submicron size polystyrene spheres as a mask. A significant photocurrent increase was experimentally demonstrated for a-Si:H p-i-n top sub-cells deposited on SiNWs. While bottom a–Si:H/c–Si heterojunction sub-cells formed on the surface with SiNWs demonstrate strong light trapping effect, which leads to enhanced external quantum efficiency in the long wavelength region compared to planar reference cell.