Abstract: We present the effects of a chlorophyll extract from diatom algae as a spin-coating anti-reflection layer on surface textured silicon solar cells. The diatom extract with a refractive index value in-between Si and air can suppress the overall light reflection from the bare Si surface up to 7% over spectral regions of 350–1100 nm. Additionally, it also shows a strong photon downconversion effect within the visible light regime. Based on both optical characteristics, the short circuit current density is largely enhanced for an approximately 10% increment in the cell efficiency. Additionally, the diatom extract is also thermally stable up to 90 °C without apparent color change and any degradation of optical properties. Thus, the presented approach is simple, doable, suitable for large area application, and more importantly, it is eco-friendly.