^Developmentof high efficiency solar cells is a crucial objective to make solar energy affordable in the long run. The VHESC program initiated by the Defense Advanced Research Projects Agency program to address the need of increasing solar cell efficiency is one such development. The VHESC program comprises around 20 contributors including ANU, and has adopted a multi-junction concentrator tandem approach. ANU’s involvement in this program is to design and develop high efficiency silicon solar cells, which are to be used in conjunction with other high-band gap and low-band gap solar cells, for 50% efficient multi-junction solar cells. The VHESC program is steadily progressing and to date it has reported to develop solar cell device results summing to 42.9% efficiency. In this paper we report current progress towards the 2nd milestone of targeted efficiency for VHESC program. We also discuss various design considerations, characterization and testing of completed solar cells. Additionally, we describe experimental work to analyse and rectify problems encountered in developing the 2.5 x 8 silicon solar cells.