Heterojunction partner, Buffer layer, alternative, CdS, ZnS, CdZnS, CIGS, CIGS2, Band offset, lattice mismatch
Devices with ZnCdS/ZnS heterojunction partner layer have shown better blue photon response due to higher band gap of these compounds as compared to devices with CdS heterojunction partner layer. CdS heterojunction partner layer has shown high photovoltaic conversion efficiencies with CIGS absorber layer while efficiencies are lower with CuIn1-xGaxS2 (CIGS2). A negative conduction band offset has been observed for CdS/CIGS2 as compared to near flat conduction band alignment in case of CdS/CIGS devices, which results in higher interface dominated recombination. Moreover, it has been predicted that optimum band offsets for higher efficiency solar cells may be achieved for cells with alternative heterojunction partner such as ZnS. With varying ratio of Zn/ (Zn+Cd) in ZnxCd1-xS a range of bandgap energies can be obtained and thus an optimum band offset can be engineered. For reducing interface dominated recombination better lattice match between absorber and heterojunction partners is desirable. Although CdS has better lattice match with CuIn1-xGaxS2 absorber layer, same is not true for CuIn1-xGaxS2 absorber layers. Utilizing ZnxCd1-xS as heterojunction partner provides a range of lattice constant (between aZnS= ~5.4 Ǻ and aCdS= ~5.7 Ǻ) depending on Zn/(Zn+Cd). Therefore better lattice match can be obtained between heterojunction partner and absorber layer. Better lattice match will lead to lower interface dominated recombination, hence higher open circuit voltages. In the present study chemical bath deposition parameters are near optimized for high efficiency CIGS2 Solar cells. Effect of various chemical bath deposition parameters on device performance was studied and attempts were made to optimize the deposition parameters in order to improve the device performance.In/(In+Ga) ratio in absorber layer is varied to obtain good lattice match and optimum band alignment. Solar cells with conversion efficiencies comparable to conventional CdS/CIGS2 has been obtained with ZnxCd1-xS /CIGS2. High short current as well as higher open circuit voltages were obtained with ZnxCd1-xS as alternative heterojunction partner for CIGS2 solar cells as compared to SLG/Mo/CIGS2/ CdS / i-ZnO/ZnO:Al.
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Master of Science in Materials Science and Engineering (M.S.M.S.E.)
College of Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering;
Materials Science and Engineering
Length of Campus-only Access
Masters Thesis (Open Access)
Kumar, Bhaskar, "Zinc Cadmium Sulphide And Zinc Sulphide As Alternative Heterojunction Partners For Cigs2 Solar Cells" (2007). Electronic Theses and Dissertations. 3234.