Phase Control of RF Sputtered SnSx with Post-Deposition Annealing for Photovoltaic Device Applications
Open Access
- Author:
- Nasr, Joseph R
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 12, 2016
- Committee Members:
- Mark William Horn, Thesis Advisor/Co-Advisor
Elzbieta Sikora, Committee Member
Saptarshi Das, Committee Member - Keywords:
- Tin Sulfide
Electrical Characterization
Conductivity type
Sputtering - Abstract:
- SnS-based solar cells have the potential to achieve 24% efficiencies based on the optoelectronic properties of SnS, however, the best reported device using SnS produced less than 5% efficiency. SnS is a semiconductor material with reported direct and indirect band gaps of 1.33 to 1.55 eV and 1.07 to 1.39 eV respectively. It has a high absorption coefficient of > 10^4 cm^−1 and possesses various other ideal physical properties; it is cost efficient, non-toxic, and abundant in the Earth’s crust. Despite these material properties, SnS has been reported to have a low ionization potential of 4.7 eV. A band misalignment is, therefore, inevitable with respect to a metal contact or a heterojunction. Previously several studies suggesting that using proper top or bottom contacts and a matching heterostructure material such as CdS, one could increase the efficiency of the device to approximately 10%. Cells of this type could potentially cost less than $0.50/Watt. We have been investigating contacts to SnS, particularly have high work function electronic contacts (Pd) examined as both top and bottom. Our present work focuses on sputtering SnSx thin films from a SnS2 target. Two optimal pathways are investigated for obtaining an n-type as well as a p-type SnS material by adjusting annealing conditions so as to investigate a pseudo-homojunction photovoltaic solar cell. Depositions were conducted at a fixed power (115 W), pressure (10 mTorr), and time (10 minutes). A series of anneals were executed at temperatures ranging from 300C to 400C, lasting from 20 to 60 minutes. Our films were examined using X-ray diffraction, field emission scanning electron microscopy (FESEM), UV-Vis spectrophotometry, hot probe, four-point probe, and transmission line measurement (TLM).