AbstractIn this work, we propose a route to achieve a certified efficiency of up to 24.51% for silicon heterojunction (SHJ) solar cell on a full‐size n‐type M2 monocrystalline‐silicon Cz wafer (total area, 244.53 cm2) by mainly improving the design of the hydrogenated intrinsic amorphous silicon (a‐Si:H) on the rear side of the solar cell and the back reflector. A dense second intrinsic a‐Si:H layer with an optimized thickness can improve the vertical carrier transport, resulting in an improved fill factor (FF). In order to reduce the plasmonic absorption at the back reflector, a low‐refractive‐index magnesium fluoride (MgF2) is deposited before the Ag layer; this leads to an improved gain of short circuit current density (Jsc). In total, together with MgF2 double antireflection coating and other fine optimizations during cell fabrication process, ~1% absolute efficiency enhancement is finally obtained. A detailed loss analysis based on Quokka3 simulation is presented to confirm the design principles, which also gives an outlook of how to improve the efficiency further.