Solution-processed Ultrathin SnO2 Passivation of Absorber/Buffer Heterointerface and Grain Boundaries for High Efficiency Kesterite Cu2ZnSnS4 Solar Cells
Heng Sun1, Jialiang Huang1, Jaesung Yun1, Kaiwen Sun1, Chang Yan1, Fangyang Liu1, Jongsung Park1, Aobo Pu1, Jan Seidel2, John Stride3, Martin A. Green1, Xiaojing Hao1
1School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia, Sydney, Australia
/2School of Materials Science Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia, Sydney, Australia
/3School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia, Sydney, Australia

The ultrathin SnO2 film, prepared by the successive ionic layer adsorption and reaction (SILAR) method, was applied between p-type Cu2ZnSnS4 (CZTS) and n-type CdS layers to passivate the interface as well as the top section of CZTS grain boundaries. With the aid of this layer, electric properties have been significantly improved. The device efficiency improved from 6.82% to 8.47%, which is mainly contributed by the boost of fill factor (FF) and open circuit voltage (Voc). However, the further increase of SnO2 thickness results in decreased Jsc and FF. Kelvin Probe Force Microscopy (KPFM) unveils the passivation of grain boundaries (GBs) of CZTS with the SnO2 coating. This work shows a new insight into the heterointerface and GBs passivation for high efficiency CZTS solar cells.