We demonstrate high-efficiency heterojunction (HJ) solar cells realized by epitaxial growth of thin layers of highly-doped Si on crystalline Si (c-Si) and crystalline Ge (c-Ge) substrates using plasma-enhanced chemical vapor deposition (PECVD) at temperatures as low as 150°C. We have achieved a conversion efficiency of 21.4% on p-type c-Si substrates textured by random pyramids and Al-doped zinc oxide (ZnO:Al) electrodes sputtered at room-temperature. To the best of our knowledge, this is the highest conversion efficiency reported for HJ solar cells on p-type c-Si substrates. We have achieved conversion efficiencies of 5.9% and 6.4% on n-type and p-type c-Ge substrates, respectively, which are comparable with efficiencies reported for conventional c-Ge cells requiring process temperatures up to 600°C. © 2012 IEEE.