Thin Film Solar Cells


Solar energy is one of the most important green energies. The solar cell market grows at an annual rate of 25%30% and the learning curve yields a factor of two drop in cost every 810 years, which makes it an attractive market. In spite of the lower conversion efficiencies of the Si-based solar cells compared with the compound semiconductor solar cells, they are the dominate mass production technology, i.e., > 90%. The conversion efficiency decreases in the order of sc-Si > poly-Si > μc-Si > a-Si. the thin-film approach is promising because it provides many advantages, such as small amount of composing materials with unlimited supplies at low costs, low-energy fabrication processes, and large-area substrate capability. The thin-film poly-Si solar cell is promising for commercial applications for its high conversion efficiency and stability. However, the biggest challenge in thin-film poly-Si solar cell fabrication is how to form the intrinsic and doped poly-Si thin films at a high rate under a low thermal budget condition so that the large-size, low-cost substrate, such as glass, used.

We have successfully prepare the thin film poly-Si film on glass used the pulsed rapid thermal annealing (PRTA) method based on the vertical Ni-enhanced solid phase crystallization mechanism. Individual intrinsic and doped a-Si thin films were transformed into polycrystalline films. In addition, the a-Si pin stack has also been transformed into the poly-Si stack.

 


PRTA Poly-Si Thin Film Formation Process

Figure Programmed and actual temperature profiles of a 10-pulse PRTA process.

35th IEEE Photovoltaic Specialist Conference Proceeding, 2010.

Poly-Si Thin Films

a-Si DP 30cm

ag-DP-20cm-Si

 

Figure Electron diffraction patterns of a PECVD a-Si nip stack (a) before and (b) after a 10-pulse PRTA process.

35th IEEE Photovoltaic Specialist Conference Proceeding, 2010.

 

Figure XRD of a PECVD intrinsic a-Si film after dehydrogenation and a 10-pulse PRTA process (1s 850C-5s cooling ).

35th IEEE Photovoltaic Specialist Conference Proceeding, 2010.

 

 

Mechanism of Crystallization

 

(a) (b)

 

Figure (a) NiSi2 formation at the early stage and (b) after propagation through the complete nip stack.

35th IEEE Photovoltaic Specialist Conference Proceeding, 2010.

 

 

Film Thickness Effect on Grain Structure

 

Figure 4. Raman spectra of poly-Si films formed from 30 nm and 100 nm thick intrinsic a-Si films after 10-pulse PRTA process.

Zhu, Kuo, Lin, and Wang, 2011 MRS Proc. 1321, a-03-05 (2011)

 

 


 

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