KCu₃S₂—Synthesis and Optoelectronic Properties of a Potential Absorber Material for Photovoltaics

A possible replacement that alleviates the shortcomings of the dominant light absorbers in solar photovoltaics is synthesized, and its microstructural, electronic structure, and optical properties are investigated. P-type KCu₃S₂ microcrystals are synthesized using the conventional carbonate method. Structural and morphological properties and composition have been determined using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The compound with nominal composition, K_0.82Cu_2.83S₂, exhibits a direct bandgap of 1.68 eV with a hole concentration of 9.18×10¹⁹cm³. Furthermore, DFT calculations confirm the directly allowed electronic transitions and indicate a high optical transition probability, leading to a remarkably high optical absorption coefficient of 10⁵ cm⁻¹ in the visible region. This yields a theoretical spectroscopic limited maximum efficiency (SLME) of 26.7% for a film of 7 to 10 μm thick of KCu₃S₂, making it a highly promising candidate as a light absorber in single junction and tandem photovoltaic devices. Moreover, the limiting factors, high carrier concentration, and large bandgap (for single junction solar cell) were tuned by doping with Sb and Se.