As optical and electronic devices evolve to become lighter, thinner, and more flexible, the substrate choice continues to be critical to their overall optimization. The substrate directly affects improvements in the designs, materials, fabrication processes, and performance of advanced electronics. With their inherent benefits such as surface quality, optical transmission, hermeticity, and thermal and dimensional stability, ultra-slim flexible glass substrates enable high-performance flexible devices. In addition, the reduction in glass thickness also allows for new device designs and high-throughput, continuous manufacturing enabled by roll-to-roll processes. This paper provides an overview of the most recent flexible glass R2R results on high temperature vacuum deposition and photovoltaic device fabrication.