Improvement of VOC in Cu2ZnSnS4 monograin layer solar cells with tin oxide inter-layer

To verify the positive effect of thin tin oxide layer on the surface of CZTS to solar cell V_OC, a thin layer of SnO_x was deposited onto the CZTS mono grains by ALD. For confirmation of the effect, the SnO_x layer was tested in combination with two different buffer materials - CBD CdS and ZnO,S. The deposition of a SnO_x inter-layer resulted in increased V_OC of CZTS/CdS solar cell from 666 mV to 724 mV and CZTS/ZnO,S solar cell from 617 mV to 719 mV. The tin oxide layer did not affect the FF and jSC values, so the improvement in V_OC led to a direct improvement in CZTS/CdS solar cell PCE. EQE measurements did not show any shift in material absorption edge/band gap, hence the V_OC increase can be fully attributed to the interface improvements, like to a reduced interface recombination rate. Apparently the additional SnO_x layer seems to allow for better collection of the carriers at longer wavelength region (650 nm - 750 nm).