Enhancing light absorption in a thin film silicon tandem solar cell fabricated on a reactive ion etched nano-structured glass surface

Abstract

The efficient capture and absorption of light are important aspects in improving the photovoltaic conversion efficiency of a solar cell. In a two-terminal tandem device, the output current density is limited by the lowest current-generating component sub-cell. We attempted by experiment to improve the current density of both sub-cells, using an inverted pyramid-type textured glass substrate. One of the two surfaces of the glass substrates was textured by semi-anisotropic reactive ion etching (RIE) with a 100 sccm flow rate of SF6 gas, and with 7 µm × 7 µm square-shaped etch masks, and obtained an optimum texture of base dimension ~7 µm, height ~8.5 µm, tip diameter ~75 nm and tip to tip separation between neighboring pyramids were about 9 µm. Tandem solar cells that were fabricated on these textured surfaces receive light from the base of these micro-pyramids, thereby enhancing light absorption in the active layers of the device. The shape of the texture and orientation of layers of the tandem solar cell ensured a longer optical path inside the solar cell, leading to higher optical absorption and an improvement in device performance. We observed an increase in the short circuit current density from 11.52 to 14.30 mA cm−2, and in the device efficiency from 11.97% to 14.22%.