Silicon nanopillars array surface texturing for solar cell application.
Wong, She Mein.
Date of Issue2012
School of Electrical and Electronic Engineering
Silicon (Si) has been used as the most common light absorber material in solar cell applications, and is expected to be the dominant photovoltaic (PV) material due to its abundance, environmental friendliness, and a well developed process technology in the future too. The conventional solar cell utilizes high-cost single-crystalline Si as its absorber material. This is because the long minority carrier diffusion length of a highly pure material allows for efficient collection of the photo-generated carriers. However, the single-crystalline Si must be thicker than the optical thickness (the film thickness of a semiconductor required to absorb 90% of the solar spectrum, which is 125 µm for Si) to absorb the solar spectrum effectively. PV modules exploiting low-grade Si thin films (e.g. poly-crystalline Si, multi-crystalline Si, and amorphous Si thin film) to reduce the manufacturing cost typically suffer from relatively low power conversion efficiency compared to the conventional crystalline silicon modules. This is due to its poor solar spectrum absorption (limited by the film thickness) and inefficient photo-generated carrier collection. One of the promising novel approaches to improve the efficiency of the thin film solar cells is to enhance their light trapping by surface texturing. Arrays of Si nanopillar (SiNP) or also known as Si nanowires (SiNW), have attracted much attention for solar cell applications stemming from their property of strong antireflection and the capability of decoupling the light absorption and photo-generated carrier collection. With SiNP array surface texturing, the optical path lengths of the incident photons are prolonged by the interaction between the incident light and SiNP arrays, enhancing the total light absorption to compensate for the efficiency loss caused by the reduced material quality and quantity. This thesis studies the optical and electrical properties of Si nanopillar arrays via simulation and a design guideline is provided for optimum cell power conversion efficiency. The thesis then experimentally explores the impact of the large-scale rational design based periodic SiNP array structural parameters (e.g. diameter/ periodicity/ height) on the reflectance and hence the absorption of the SiNP, and the results are in consistent with the theoretical prediction. A record high short circuit current density (Jsc) of 30.96 mA/cm2 as of 2011 is achieved using axial p-n junction SiNP surface textured solar cell. This implies the SiNP array is a suitable and promising texturing technology for photovoltaic application.
DRNTU::Engineering::Electrical and electronic engineering::Nanoelectronics