CuSbS2 as a Promising Earth-Abundant Photovoltaic Absorber Material: A Combined Theoretical and Experimental Study

Recently, CuSbS2 has been proposed as an alternative earth-abundant absorber material for thin film solar cells. However, no systematic study on the chemical, optical, and electrical properties of CuSbS2 has been reported. Using density functional theory (DFT) calculations, we showed that CuSbS2 has superior defect physics with extremely low concentration of recombination-center defects within the forbidden gap, espeically under the S rich condition. It has intrinsically p-type conductivity, which is determined by the dominant Cu vacancy (VCu) defects with the a shallow ionization level and the lowest formation energy. Using a hydrazine based solution process, phase-pure, highly crystalline CuSbS2 film with large grain size was successfully obtained. Optical absorption investigation revealed that our CuSbS2 has a direct band gap of 1.4 eV. Ultraviolet photoelectron spectroscopy (UPS) study showed that the conduction band and valence band are located at 3.85 eV and −5.25 eV relative to the vacuum level, respectively. As the calculations predicted, a p-type conductivity is observed in the Hall effect measurements with a hole concentration of ∼1018 cm–3 and hole mobility of 49 cm2/(V s). Finally, we have built a prototype FTO/CuSbS2/CdS/ZnO/ZnO:Al/Au solar cell and achieved 0.50% solar conversion efficiency. Our theoretical and experimental investigation confirmed that CuSbS2 is indeed a very promising absorber material for solar cell application.