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 Zn 1− x Sn x O y (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)%.