Enhancing the Photovoltaic Performance of Cu_2ZnSn(S,Se)_4 Solar Cells with Ba Trace Doping: Large Chemical Mismatch Cation Incorporation

摘要

Being absent from larger mismatch of ionic radius and chemical coordinationbetween the cations in Cu_2ZnSn(S,Se)_4 (CZTSSe) can aggravate the formation ofdetrimental cation antisite defects and clusters with low formation energy, whichresults in a serious open-circuit voltage deficit and a challenge for higher powerconversion efficiency of CZTSSe solar cells. External cation doping or alloying is amore effective strategy to solve this issue. Herein, samples of trace Ba dopinginto CZTSSe are fabricated by the sol–gel method and the mechanism of suchtrace Ba doping are studied combined by X-ray diffraction (XRD), Raman, andphotoluminescence (PL) measurements. The performance of CZTSSe solar cellsis increased by 25.7% as 1% Ba is doped into CZTSSe to substitute Zn. Theresults highlight the roles of the trace Ba doping on the performance of CZTSSesolar cells, which is beneficial to the reduced formation of the detrimental defectsand associated clusters. As a consequence, the bandgap fluctuations are reduced,which results in the improvement of VOC and thus the performance of the solarcell. The cation substitution engineering with larger chemical mismatchedalkaline-earth metal cations provides insights for further improvement of CZTSSesolar cells based on earth abundant elements.