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Investigation of Thermal Stress Effect on The Performance of Thin Film Solar Cells Using Finite Element Method

Namvar, Arman | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48137 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Sohrabpour, Saeed
  7. Abstract:
  8. Thin film solar cells have low efficiency compared to crystalline silicon solar cells; however, they are low-cost and flexible. In manufacturing these solar cells, thin films are deposited at high temperatures (higher than 200℃) on a thick metal, plastic, or glass substrate using sputtering and plasma enhanced chemical vapor deposition (PECVD) methods. Since the thin films and substrate have different thermal expansion coefficients, cooling the system from deposition temperature to room temperature induces thermal residual stresses in both the films and substrate. In addition, these stresses, especially those induced in the amorphous silicon layer can change the carrier mobility and band gap energy of the silicon and consequently affect the solar cell efficiency. Thus, the purpose of this thesis is investigation of thermal residual stresses and their effects on the performance of amorphous silicon thin film solar cells. The performance of a solar cell is analyzed based on its important parameters such as efficiency and output power. These important solar cell parameters can be calculated via optical and electrical modeling. In this study, both the optical and electrical models are developed using finite element method. Subsequently, the simulation results are validated with experimental data. 2D and 3D finite element models are proposed to calculate thermal residual stresses in silicon thin film solar cells. One of the main features of the proposed finite element models is to remove the need for a full scale model. The models are verified by the available analytical results in the literature. Also, advantages and disadvantages of each finite element model are discussed. Then using the proposed models, the thermal residual stresses are studied in a commercial amorphous silicon thin film solar cell for different deposition temperatures, and subsequently, the simulation results are validated with experimental data. It is shown that for the deposition temperatures of 200 and 300℃, the biaxial residual stress in the amorphous silicon layer reaches -367 MPa and -578 MPa, respectively, which are large values and hence should be considered accurately in the solar cell designs. Finally, effects of both temperature and thermal stress on the performance of silicon thin film solar cells are investigated using the proposed models. The results illustrate that there is a good agreement between the simulation results and experimental ones. It is shown that as the operating temperature of the thin film solar cell installed in Tehran increases during a day of June, its efficiency drops by 12.7%
  9. Keywords:
  10. Temperature Effect ; Finite Element Analysis ; Thin Film Solar Cell ; Amorphous Silicon ; Optical/Electrical Modeling ; Thermal Residual Stress

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