We have developed heterojunction interdigitated back contact solar cell with conversion efficiency of 26.6% (designated area: 180 cm(2)) independently confirmed by Fraunhofer Institute for Solar Energy system Callab. Compared to our previous record efficiency (26.3%), the 0.3% absolute improvement can be regarded as similar to 10% reduction of remaining losses to the theoretical limit (similar to 29%). We discuss the analyzed cell properties together with our recent progress to predict how far we can go in reducing the remaining losses in silicon photovoltaic.