Rietveld analysis of CuBiSeCl2 PXRD data, shown in Figure , was used to confirm the structural model determined from SCXRD data and demonstrated phase purity of the bulk samples. TEM images (S18) show the particles to be needle-like structures of approximately 1.5 μm × 0.25 μm. Compositional analysis was performed on both single crystal and powder samples of CuBiSeCl2 to corroborate the stoichiometry determined from the single crystal model, as shown in S19-23. SEM-EDX elemental mapping was performed on a single crystal of CuBiSeCl2 to confirm homogenous distribution of elements, as well as the absence of oxygen in the structure. Single crystal EDX elemental mapping in Figure indicates that Cu, Bi, Se and Cl are all uniformly distributed in the sample, and the presence of oxygen is minimal. To further confirm the material stoichiometry and account for the significant overlap of Bi 3+ and Cl -peaks in The band structure and effective masses were calculated for CuBiSeCl2 to provide insight into the optical band gap and mobility of charge carriers within the material, as well as elucidate possible applications. The band structure of CuBiSeCl2 is shown in Figure (a). The band gap calculated from this band structure is found to be 1.5 eV, suggesting that CuBiSeCl2 may have potential as a solar absorber. As such, it is important to understand the behaviour of charge carriers within the material. This may be understood from the calculated effective masses, shown in Table . The effective masses are reported for the Γ → X, Γ → Y, Γ → Z directions.