Improving efficiency of electrostatic spray-assisted vapor deposited Cu2ZnSn(S,Se)4 solar cells by modification of Mo/absorber interface

• Ultrathin ZnO layer between CZTSSe and Mo minimizes absorber decomposition.
• CZTSSe is deposited by ESAVD.
• ZnO layer no longer exists after selenization treatment.
• Improved efficiency for ESAVD-deposited kesterite of 4.03%.

Electrostatic spray-assisted vapor deposition (ESAVD) is a non-vacuum, low cost and eco-friendly method to produce Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 (CZTSSe) absorbers for thin film solar cells, and it is a very promising method for industrialization due to it is high deposition speed and close to unity deposition efficiency. In this work, in order to improve the efficiency of ESAVD deposited CZTSSe solar cells, an ultrathin ZnO (circa 10 nm) layer was employed as an intermediate layer between CZTSSe and Mo back contact to avoid the direct contact between Mo and CZTSSe and reduce the decomposition of CZTSSe during annealing process. XRF and EDX were used to characterize the chemical composition of CZTSSe before and after selenization respectively. SEM and Raman results showed the improved absorber morphology and the reduced direct interfacial reaction between CZTSSe and Mo. The improvement of the CZTSSe/Mo interface due to the intermediate layer was also reflected in the quality of the derived photovoltaic devices, leading to an improved efficiency of ESAVD-deposited kesterite solar cells from 3.25% to 4.03%.