Solution-Processed Air-Stable Copper Bismuth Iodide for Photovoltaics.

Area of Science:

• Materials Science
• Photovoltaics
• Semiconductor Physics

Background:

• Bismuth-based semiconductors are emerging as efficient, non-toxic alternatives for photovoltaic applications.
• Copper bismuth iodide (CuBiI₄) is a novel material within this class, showing promise for solar cell technology.

Purpose of the Study:

• To synthesize and characterize a long-term stable copper bismuth iodide (CuBiI₄) material.
• To investigate the photovoltaic performance and stability of CuBiI₄ solar cells.
• To explore the potential of CuBiI₄ as a short-wavelength absorber in tandem solar cells.

Main Methods:

• Solution-processed synthesis of CuBiI₄ films in an air atmosphere using a HI-assisted dimethylacetamide (DMA) co-solvent.
• Solvent vapor annealing (SVA) with tributyl phosphate at low temperatures (≤70°C) to achieve uniform, dense films.
• Characterization using X-ray diffraction (XRD) for crystal structure analysis and photoluminescence/Hall effect measurements for carrier properties.

Main Results:

• Achieved a stable, uniform, and dense CuBiI₄ film with improved grain size, photoluminescence lifetime, and hall mobility (110 cm² V^-1 s^-1).
• Determined the cubic crystal structure (space group Fd3m) with a [111] preferred orientation.
• Demonstrated a wide bandgap (2.67 eV) solar cell with 0.82% power conversion efficiency and exceptional long-term stability (>1008 hours) under ambient conditions.

Conclusions:

• Copper bismuth iodide (CuBiI₄) is a promising, air-stable, non-toxic semiconductor for photovoltaic applications.
• The developed synthesis method yields high-quality films with enhanced optoelectronic properties.
• CuBiI₄ solar cells exhibit significant long-term stability, making them suitable for future tandem solar cell designs.