PROSPECTS OF BACK CONTACTS WITH BACK SURFACE FIELDS IN HIGH EFFICIENCY ZnxCd1-xS /CdTe SOLAR CELLS FROM NUMERICAL MODELING

摘要

Zinc Cadmium Sulfide (ZnxCd1-xS) thin films have been recognized as good candidates in photovoltaic devices acting as wide-bandgap window layer. Results of numerical analysis using AMPS-1D simulator in exploring the possibility of ultra thin, high efficiency and stable ZnxCd1-xS /CdTe solar cells are presented. A baseline structure of CdS/CdTe cell was explored in this work with reduced CdTe absorber layer and ZnxCd1-xS has been replaced to CdS as window layer, where 1 μm thin CdTe and 80 nm ZnxCd1-xS layers showed reasonable efficiencies over 18%. The viability of 1 μm CdTe absorber layer together with possible back surface field (BSF) in ZnxCd1-xS/CdTe cells was investigated. Moreover, the variation of x in ZnxCd1-xS was analysed for high efficient cell and the optimal value of x was found to be 8%. The proposed structure of SnO2/Zn2SnO4/CdS/CdTe/As2Te3/Cu showed the highest conversion efficiency of 18.9% (Voc = 0.92 V, Jsc = 24.98 mA/cm2 and FF = 0.82). However, other proposed structures such as SnO2/Zn2SnO4/CdS/CdTe/Sb2Te3/Mo and SnO2/Zn2SnO4/CdS/CdTe/ZnTe/Al showed better stability at higher operating temperatures. Moreover, it was found that the cells normalized efficiency linearly decreased with the increased temperature at lower gradient, which eventually indicates better stability of the proposed ultra thin ZnxCd1-xS /CdTe cells.