We have achieved the world's highest solar cell conversion efficiency of 22.3% (V(oc): 0.725 V, I(sc): 3.909A, FF: 0.791, total area: 100.5 cm(2), confirmed by AIST) by using a heterojunction with intrinsic thin layer (HIT) structure. This is the world's first practical-size (> 100 cm(2)) silicon solar cell that exceeds a conversion efficiency of 22% as a confirmed value. This high efficiency has been achieved mainly due to improvements in a-Si:H/c-Si hetero-interface properties and optical confinement. The excellent a-Si: H/c-Si hetero-interface of the HIT structure enables a high V(oc) of over 0.720V and results in better temperature properties. In order to reduce the power-generating cost, we are now investigating numerous technologies to further improve the conversion efficiency. especially the V(oc), of HIT solar cells. with the aim of achieving 23% efficiency in the laboratory by 2010. (C) 2008 Elsevier B.V. All rights reserved.