CZTS solar cells and the possibility of increasing VOC using evaporated Al2O3 at the CZTS/CdS interface

•CZTS solar cells with and without Al2O3 very thin layer was used on the CZTS/CdS interface.•Al2O3 thin layer was deposited by thermal evaporation.•An increase in Voc with the use of thermally evaporated Al2O3 was demonstrated.•A band diagram of the structure CZTS/Al2O3/CdS/ZnO/ITO showed a difference on energy in VBO.