The corrected pDoS indicates that Cu 3d states dominate the top of the valence band, whilst Cl 3p states occupy higher binding energies much deeper into the valence band. Se 4p, Cu 3p, and to a lesser extent, Bi 5p / 5d states, cover a broad range of binding energies between 0 and 6 eV in the valence band. There is some hybridization between the Cu 3d, Se 4p and Cl 3p states at higher binding energy in the valence band, likely due to the overlap of Cu, Se and Cl orbitals in the octahedral CuSe2Cl4 bonding environment. Similarly, hybridization between Bi 5p and Se 4p / Cl 3p states at the A sharp peak arising from Cu orbital contributions is also observed in the pDoS of similar chalcogenide and chalcohalide materials, including Cu3BiS3 (P212121) and Bi2CuSe3I (C2/m), in which Cu occupies different bonding environments. This suggests that Cu has a commanding effect over both chalcogen and halogen orbitals across different structures with similar chemistries, heavily influencing the top of the valence band. Comparisons between the CuBiSeCl2 and CuBiSCl2 pDoS reveals that the electronic structure is robust to the Cu displacement, as there is no significant difference between the contributions of Cu orbitals to the pDoS of either material. It is likely that the increased overlap of Cu and Cl states in the direction of Cu displacement is negated by the reduction in Cu-Cl orbital overlap in the opposite direction. Excellent agreement is observed between the XPS data and the pDoS, suggesting that the DFT calculations provide accurate insights into the electronic character of the material. To enable the development of thin films and prototype devices based on CuBiSeCl2, it is essential to understand the band alignments of the material to allow selection of suitable device structures and n-type window layers. Figure (b) depicts the band alignments for CuBiSeCl2 alongside well-established semiconductors with similar chemistries, Cu2ZnSnS4 (CZTS) and CuInxGa1-xSe (CIGS). By collecting the secondary electron cut-off region using very low power XPS, it was possible to determine the ionisation potential and the Valence Band Minimum (VBM) (full description in the Supporting Information S28 -30). The Conduction Band Minimum (CBM) could then be located using the band gap, determined from diffuse reflectance UV-Vis Spectroscopy, and found to be 1.40 (3) eV in good agreement with computational predictions. CdS has already been demonstrated as a successful window layer for CZTS and CIGS and, given the comparable band alignments, could also find application as a suitable window layer for devices based on CuBiSeCl2.