This study investigates the thermodynamic performance of a single-effect absorption refrigeration system using R1243zf/[Hmim][PF6] and R1243zf/[Omim][PF6] as the two binary working pairs. The low-GWP refrigerant R1243zf is combined with 1-hexyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium hexafluorophosphate, respectively. The vapor–liquid equilibrium behavior was correlated using the non-random two-liquid (NRTL) model, and the system was evaluated in terms of circulation ratio, solution concentration difference, coefficient of performance, exergy efficiency. The results show that the ionic-liquid cation structure significantly affects refrigerant solubility and cycle performance. R1243zf/[Omim][PF6] exhibits a lower circulation ratio and higher COP than R1243zf/[Hmim][PF6], mainly because of its larger effective solution concentration difference.The exergy efficiencies remain relatively low, approximately 0.10–0.12, owing to the low-grade heat-source condition and internal irreversibility of the single-effect cycle. This work provides a thermodynamic basis for developing R1243zf/imidazolium-based ionic-liquid working pairs for low-temperature heat-driven refrigeration.