The Fourth Workshop on Optics for Solar Energy will be held on 09-10 October 2023. The workshop is organized by Helmholtz-Zentrum Berlin für Energie und Materialien and Zuse Institute Berlin, in cooperation with OptecBB. Current trends and developments in the field of optics and nanophotonics for solar energy conversion devices will be discussed. The workshop will be organized as part of Photonics Days Berlin Brandenburg 2023 at Berlin-Adlershof.