The efficiency of a heterojunction with intrinsic thin‐layer (HIT) solar cell with an insulator/ITO structure was discussed in this paper. First, the efficiency was analyzed by OPAL 2 simulations. Second, an insulator/ITO structure was experimentally applied to a HIT solar cell. The OPAL 2 simulations using an insulator/ITO/Si structure and a TCO/ITO/Si structure showed that the generation current density in the Si substrate increased when the insulator or TCO layer had a proper thickness. Experimentally, HfO_2, a type of insulator, was deposited on a HIT solar cell with a thickness varying from 3 to 15 nm. The average efficiency of the HIT solar cell improved from 18.21% to 20.75% after HfO₂ deposition. The highest efficiency was achieved for the 3‐nm‐thick HfO₂/HIT solar cell structure, which exhibited the best improvement in the current density of approximately 1.5 mA/cm². For the external quantum efficiency of the HfO₂/HIT solar cell, the total absorption was improved by HfO₂ deposition. The results suggest that the HfO₂ layer improves the solar cell efficiency of the HIT solar cell by increasing light absorption.