| Although CIS and Cd Te based solar cells have achieved a big progress in conversion efficiency, the fact that toxicity of cadmium and availability of indium probably limits their future development. As an alternative, the indium-free kesteriate semiconductor materials Cu2 Zn Sn S4(CZTS) has similar photoelectrical properties with CIS and it`s becoming a promising absorber for solar cells. It is direct band gap semiconductor and the absorption coefficient is bigger than 104cm–1. The components of Cu?Zn and Sn are earth-abundant and environment friendly. Many synthesis methods based on vacuum and non-vacuum skills have been developed and high efficient CZTS solar cells have been made. TCu/Zn/Sn precursor(CZT) film was deposited on soda-lime glass substrate by sputtering machine. The CZT film was flat and compact, and XRD patterns of precursors revealing that Cu6Sn5 and Cu5Zn8 binary phases and tin phase exist in the precursors. This is in agreement that zinc and tin prefer to react with copper, rather than forming Znx Sny alloy or CZT ternary alloy. The CZT film was deposited with a layer of Se film before annealing. It is shown that increasing the conversion pressure and the Se film thickness can reduce the loss of Sn element and binary selenides. Because of the different thermodynamic property between CZT metallic precursor film and Se film, there are many selenide balls on the film`s surface. On the other hand, the loss of Sn elements will make the CZTSe decompose into binary or tenary selenides. This condition was improved by using Se gas as resource. The crystallinity and surface morphology were better than before and carrier mobility achieved 1 cm2V–1s–1 for first time.Cu2O?Sn O and Zn S powder were first used as resource to synthesize CZTS film. Powders were milled through wet ball-mill approach and deposited onto substrate by Doctor Blade method. It is found that the precursor film can be sulfurated by using H2/N2 with S gas.The CZTS made by this method shows strong XRD ampliture and no binary sulphide phases were found,but there is a weak Cu2 O peaks. The sulfurated Cu-S compound will cover the Cu2 O inside and inhibit futher sulfuration process. This condition can be improved by increasing the sulfuration time or reduce the size of Cu2 O powders. CZTS film was selenizing with Se gas and its crystal structure and surface morphology were characterized. It is shown that 80% S atoms were substitute by Se atoms. The ratio of Cu/(Zn+Sn) is close to 1. The grain size is bigger than 2?m and many grains compact together.SCAPS-1D softeware is employed to simulate and calculate the CZTS solar cells` output performance. The basic structure of CZTS solar cells was built and photoelectric parameters for each layer were input into software. The influences of CZTS layer thickness, carrier density and CZTSSe bandgap were studied. The results show that nearly 2?m thickness of CZTS layer is enough for spectral absorption. Cell`s efficiency can be enhanced by increasing CZTS layer thickness, but there is no obvious improvement when CZTS layer>5?m. Although high carrier density can increase the Voc,it will reduce the Jsc of solar cell. It is necessary to make a trade off about carrier density. The bandgap of CZTSSe shows almost linearly trend with Se/(Se+S) ratio which can adjust the Vocand Jscof cells. The result shows that the CZTS solar cell will reach it highest efficiency(21.1%) when Se/(Se+S) = 0.3... |
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