Zn 1− x Sn x O y Buffer Layer Deposited by Chemical Bath Deposition for Low and Wide Bandgap Cu(In, Ga)Se ₂ Solar Cells

Cu(In, Ga)Se 2 (CIGSe) solar cells with a tunable bandgap stand out as a promising technology for tandem applications. Addressing the environmental concerns associated with Cd‐based buffers, this study investigates the suitability of zinc tin oxide (ZTO), deposited via chemical bath deposition (CBD), as a Cd‐free alternative for both low‐bandgap CIGSe and wide‐bandgap (Ag, Cu)(In, Ga)Se 2 (ACIGSe) solar cells. Best ZTO‐buffered devices exhibit competitive power conversion efficiencies (PCE) of 14% and 7% for low‐bandgap and wide‐bandgap absorbers, respectively. The optimal tin concentration for ZTO buffer layers vary, with 10% [Sn]/([Sn] + [Zn]) ratio (TTZ) identified as optimal for wide‐gap ACIGSe and 20% TTZ for low‐gap CIGSe. A performance decline beyond optimal tin concentrations could be linked to losses in open‐circuit voltage. In summary, ZTO‐based devices showcase promising photovoltaic performance, emphasizing ZTO's potential as a practical and nontoxic alternative, deposited by CBD, to traditional CdS for diverse CIGSe solar cell applications.