Chemical Bath Deposition of Zn1-xSnxOy Films as Buffer Layers for Cu(In,Ga)Se2 Solar Cells

Cu(In,Ga)Se-2 (CIGSe) thin-film solar cells are a commercial photovoltaic technology that provides sustainable power. Herein, the formation of Zn1-xSnxOy (ZTO) thin films is studied as Cd-free buffer layer by chemical bath deposition (CBD) suitable for CIGSe solar cell devices. ZTO films are obtained by CBD onto soda lime glass, by modifying a reported procedure otherwise leading to columnar ZnO thin films. These ZTO films show a flatter morphology compared to the reference ZnO due to inhibition of the columnar growth. In addition, a nontrivial increase in the bandgap is observed by enhancing Sn concentration. When a concentration of 20% [Sn]/([Sn] + [Zn]) (where [Sn] and [Zn] are the molar concentrations of Sn and Zn, respectively) is employed in the chemical bath, the resulting buffer layer allows the CIGSe solar cell to achieve similar performance as with a CdS buffer layer (average efficiency of (11 +/- 2)%), yielding a maximum efficiency of 10.4%, with an average of (9 +/- 2)%.