Chemical and Biological Engineering ETDs

Publication Date

Spring 5-15-2019


In this dissertation, we enhance the efficiency of thin flexible monocrystalline silicon solar cells by breaking symmetry in light trapping nanostructures and improving homogeneity in dopant concentration profile. These thin cells are potentially less expensive than conventional thick silicon cells by using less silicon material and making the cells more convenient to be handled when supported on polymer films. Moreover, these cells are widely applicable due to their flexibility and lightweight. However, for high efficiencies, these cells require effective light trapping and charge collection. We achieve these in cells based on 14-mm-thick free-standing silicon films with light-trapping arrays of nanopyramidal dips fabricated by wet etching.

We break the symmetry of nanopyramids by etch mask design and its rotation with respect to a crystallographic direction in silicon substrate. This approach eliminates the need for using expensive off-cut silicon wafers. We also make use of low-cost, manufacturable, wet etching steps to fabricate the nanopyramidal dips. In our experiment, the new symmetry-breaking approach enhances the cell efficiency by 1.1%.

In light-trapping nanostructures, the texture size is comparable to or smaller than the characteristic diffusion length of a dopant. In this size regime, strong inhomogeneity in the dopant concentration often develops in the pn-junction of the cells. The strong inhomogeneity creates electrically inactive regions in the texture. We improve the homogeneity by diffusing a dopant through selective surface regions exposed by wet etch masks. Our experiments demonstrate that this dopant diffusion method enhances the cell efficiency by 0.8%. This method would be generally applicable for other micro/nano structures, semiconductor materials, and optoelectronic devices.


Crystalline silicon solar cells, Light trapping, Dopant diffusion, Inverted nanopyramid structure, Nanotructure

Document Type




Degree Name

Chemical Engineering

Level of Degree


Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Dr. Sang Eon Han

Second Committee Member

Dr. Sang M Han

Third Committee Member

Dr. Ganesh Balakrishnan

Fourth Committee Member

Dr. Tito Busani