S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Materials Science and Engineering (재료공학부) Theses (Ph.D. / Sc.D._재료공학부)
Designing Transparent Electrodes Materials Toward Broadband Light Trapping
- 공과대학 재료공학부
- Issue Date
- 서울대학교 대학원
- 학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2015. 8. 박병우.
- Transparent conducting oxides (TCOs) have been used for various
optoelectronic applications, such as flat-panel displays and thin-film solar cells.
Especially for a-Si thin-films solar cells, light-scattering capability of TCOs via
surface texturing is one of the most important characteristics due to effective
scattering enhances power-conversion efficiency. Among various TCOs, ZnO:Al
has received strong attention because of its larger feature size by wet-chemical
etching. Basically, textured morphology by wet etching depends on the
nanostructure of TCOs due to the anisotropy of etching rates. However,
nanostructural control of TCOs in mass manufacturing is pretty limited with
consideration of electrical conductivity and high throughput. Therefore, surface
texturing by simple etching for the given TCO nanostructures offers a great merit
for the strategy of TCO development.
In this thesis, the novel etching system by organic acid for the surface-textured
ZnO:Al films is investigated. The Chap. 1 describes the general scientific context
and the research field in which this thesis is included. First, a brief overview of
the photovoltaic technologies and the current issues of the Si thin-film solar cells.
Second, the TCOs are introduced and their use as a front electrode in Si thin-film
solar cells is explained. Finally, the motivation and objectives of this work are
In Chap. 2, an organic acid for the surface texturing of ZnO:Al is introduced
as an alternative to conventional HCl. The texturing behavior by oxalic acid is
investigated in terms of vertical roughness, lateral correlation length, and thickness
change according to the crater evolution. Etching with oxalic acid results in
superior light-scattering performance (by ~8% increase at λ = 1000 nm) with
maintaining transparency and resistance, compared to etching with HCl. This
fascinating behavior is understood by crater evolution with the difference in relative
etching rates. Significantly, this simple and reproducible texturing tactic extends
tunability for desirable TCO morphology, enabling efficient light trapping, and
therefore appears potentially applicable for large-scale photovoltaic devices in
industry. Lastly, all results and conclusion of the thesis are summarized in Chap.