Development Of Cadmium Selenide As An Absorber Layer For Tandem Solar Cells

Author

Sathyaharish Jeedigunta, University of South Florida

Graduation Year

2004

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Don Morel, Ph.D.

Committee Member

Christos Ferekides, Ph.D.

Committee Member

Y.L.Chiou, Ph.D

Keywords

css, fill factor, trasmission, substrate temperature

Abstract

Cadmium Selenide is a binary compound. It has a band gap of 1.7 eV. This is one of the suitable materials for an absorber layer in the top cell of a tandem solar cell. CIGS with a low Gallium content has a band gap of 1 eV suits well as an absorber layer for the bottom cell. CIGS cells have already attained an efficiency of 15% [1,2]. Since years, research has been done in developing the bottom cell. The results of the bottom cell are promising. So the fabrication of an efficient top cell in a tandem solar cell is a challenge. To achieve a high tandem efficiency of above 25 %, the top cell has to contribute at least 2/3 of the total efficiency, which necessitates the top cell to have at least 16 to 18 % efficiency [3].

Development of a defect free absorber layer is a crucial step in this process to achieve the above goals besides optimizing other layers. Selenium vacancies in CdSe make the absorber layer n-type. CdSe is deposited by closed space sublimation. Deposition of CdSe at higher substrate temperatures in comparison to the standard conditions was studied. ZnSe acts as an insulating layer. It is thermally evaporated in an Evaporation system. Copper acts as a metal contact on top of the insulator resulting in a MIS structure. Copper is also deposited by Thermal Evaporation. Devices are fabricated on different substrates like SnO2: F, AZO etc.

Fabricated cells are characterized by J-V and Spectral response measurements. Devices fabricated on SnO₂: F substrates show typical open circuit voltages of around 220 mV, short circuit current densities of 10.02 mA/cm² and fill factors around 33 %. N-type CdS when deposited on SnO₂: F below the absorber layer further improved Voc's to around 330 mV. Annealing of these devices improved V_oc's to about 350 mV but J_sc's remained 7.21 mA/cm².

Scholar Commons Citation

Jeedigunta, Sathyaharish, "Development Of Cadmium Selenide As An Absorber Layer For Tandem Solar Cells" (2004). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/1093