Zirconium carbonitride (ZrC-ZrN) absorber layer has been optimized for the maximum absorptivity alpha similar to 0.9 in ZrOx/ZrC-ZrN/Zr reflector-absorber tandem structures on stainless steel (SS) and aluminum (Al) substrates, using reactive DC/RF magnetron sputtering process and varying reactive nitrogen during the deposition. The mechanical properties such as hardness and Young's modulus values increase from similar to 19.63 to similar to 38.53 GPa and similar to 36.39 to similar to 58.67 GPa, respectively, with increasing nitrogen flow rate during ZrC-ZrN absorber layer deposition on SS substrate. These values also increase with increasing load up to a critical limit and saturates thereafter with further increase in load values. The films with moderate hardness and Young's modulus exhibit enhanced solar thermal performance (alpha similar to 0.9) against films with lower and higher values of these mechanical properties, suggesting optimal nitrogen concentration for desired solar thermal performance.