In recent years, significant attention has been paid to the investigation of parameters associated with the absorber surface of stepped solar stills, aiming to enhance their performance. In this study, metal fins have been employed on the absorber surface to increase the absorption of radiant energy. The experiment's input variables included the inlet flow rate (100, 150, and 200 ml/min), number of fins (1, 2, and 3 fins on each step), angle of fins (−30°, 0°, and +30°), height of fins (1, 2, and 3 fins on each step), and material of the fins (copper, aluminum, and galvanized steel). 27 main experiments were designed with the help of design of experiments. Results showed that productivity decreased and increased with increasing inlet flow rates and fin numbers, respectively. In addition, the +30° fin had the best results compared to other angles, and freshwater productivity decreased with increasing fin height. Also, copper fins performed better than other fins. Finally, compared to the stepped solar still without fins, a 171 % increase in efficiency was seen in the optimal mode, which had three copper fins with a height of 3 cm, an angle of +30°, and an inlet flow rate of 100 ml/min.
