Improving Efficiency of Evaporated Cu₂ZnSnS₄Thin Film Solar Cells by a Thin Ag Intermediate Layer between Absorber and Back Contact

Abstract

A 20 nm Ag coating on Mo back contact was adopted to improve the back contact of evaporated Cu 2 ZnSnS 4 (CZTS) solar cells. The Ag layer helped reduce the thickness of MoS 2 which improves fill factor (FF) significantly; additionally, it reduced secondary phases ZnS and SnS 2− x , which may help carrier transport; it was also involved in the doping of the absorber layer, which compensated the intrinsic p-type doping and therefore drags down the doping level. The doping involvement may enlarge the depletion region and improve lifetime of the absorber, which led to enhancing open circuit voltage (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mrow><mml:mtext>O</mml:mtext><mml:mtext>C</mml:mtext></mml:mrow></mml:msub></mml:mrow></mml:math>), short circuit current density (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mrow><mml:msub><mml:mrow><mml:mi>J</mml:mi></mml:mrow><mml:mrow><mml:mtext>S</mml:mtext><mml:mtext>C</mml:mtext></mml:mrow></mml:msub></mml:mrow></mml:math>), and efficiency significantly. However, it degrades the crystallinity of the material slightly.