Experimental and Computational Studies of Solution Processed CuSbSe₂ for Photovoltaic Applications

The exploration of novel absorber materials composed by earth-abundant and low-toxicity elements is important for thin-film solar cells. Among these materials, CuSbSe₂ is promising because of its suitable optical and electrical properties such as ≈ 1.1 eV bandgap and high absorption coefficient. However, the practical application of the reported hydrazine solution process is limited by the hazardous nature of hydrazine, and more detailed investigations into charge-carrier transport properties of CuSbSe₂ is needed. In this study, a novel thiol-amine solution processing route is used to fabricate CuSbSe₂ thin films. The fundamental properties of CuSbSe₂ thin films are investigated, including phase purity, absorption coefficient and bandgap, to demonstrate the feasibility of the thiol-amine route. Next, the charge-carrier kinetics are studied by transient absorption (TA) and optical-pump terahertz-probe (OPTP) spectroscopy, which reveal that, in contrast to other heavy pnictogen-chalcogenide compounds studied recently [1], CuSbSe₂ avoids carrier localisation. To further study the carrier-phonon coupling and carrier transport properties, the temperature-dependence of the mobility is determined through Hall-effect measurements, and compared with DFT calculations to show that Fröhlich coupling dominates in CuSbSe₂. The coupling to acoustic phonons is weak, owing to low deformation potentials. The cause of the low deformation potential is studied by investigating how the lattice distorts along the dominant phonon modes. The combined experimental-computational studies shown in this work lead to new insights into how materials avoiding carrier localisation could be designed in the future.<br/><br/>References<br/>[1] Huang, Kavanagh, et al., Nat. Commun., 13, 4960 (2022)