tailieunhanh - Solar Cells Thin Film Technologies Part 2

Tham khảo tài liệu 'solar cells thin film technologies part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Thin-Film Photovoltaics as a Mainstream of Solar Power Engineering 19 deposit undoped CdS and then low-resistive CdS doped with In or Ga pre-inflicted undoped CdS layer is called the buffer layer . Due to a relatively narrow band gap eV CdS absorbs solar radiation with a wavelengths Ằ 520 nm without giving any contribution to the photovoltaic efficiency. Absorption losses in the CdS layer can be reduced by increasing the band gap alloying with ZnS CdZnS that results in some increase in the efficiency of the device. Its further increase is achieved by thinning CdS layer to 50 nm or even 30 nm followed by deposition of conductive ZnO layer which is much more transparent in the whole spectral region Jordan 1993 Nakada T. Mise 2001 . The best results are achieved when ZnO is deposited in two steps first a high-resistance ZnO layer and then a doped high-conductivity ZnO layer. Often ZnO films are deposited by magnetron sputtering from ZnO Al2O3 targets or by reactive sputtering which requires special precision control technology regime. For high-efficiency cells the TCO deposition temperature should be lower than 150 C in order to avoid the detrimental interdiffusion across CdS CIGS interface Romeo et al. 2004 . Usually Cu In Ga Se2 solar cells are grown in a substrate configuration which provides favorable process conditions and material compatibility. Structure of a typical solar cell is shown in Fig. 9. To reduce the reflection losses at the front surface of ZnO an anti-refection MgF2 coating with thickness of 100 nm is also practised. The substrate configuration of solar cell requires an additional encapsulation layer and or glass to protect the cell surface. In modules with cover glasses to use any anti-refection coating is not practical. Radiation Ni 50 nm Al 1-2 pm n-ZnO n -ZnO pm n-CdS mkm p-Cu InGa Se2 2 pm Mo pm Substrate glass metal foil plastics Fig. 9. Schematic cross section of a typical Cu In Ga Se2 solar module. CdS layer is made by .