Electrical properties and back contact study of CZTS/ZnS heterojunction

In the present work, we have studied the effect of metal back contact nature on the electrical properties of CZTS/ZnS based heterojunction prepared by spray pyrolysis. Three different back contact metals (Al, Au and Ag) were tested as alternative of the commonly used Molybdenum. Structural and optical properties of different layers are characterized. The electrical devices characterization were achieved by (I-V) at ambient and at different temperatures and capacitance-conductance vs frequency (C-G-f) measurements. The realized structures exhibit a rectifying behavior. The ideality factor of all devices were found to be large, it is found equal to 5.9 when using Au contact and equal to 10.5 and 11.4 in heterojunction prepared with Ag and Al back contact respectively. The anomalous ideality factor is due to the Schottky contact between Al, Ag and CZTS and to the presence of density of defect at the interface CZTS/ZnS. The latter was estimated from conductance measurement as a function of frequency and found equal to 1010 cm−2 eV−1. From this study we inferred that Au contact can be an alternative of Mo as back contact of CZTS based solar cell.