Recent designs in nanophotonic light-trapping technologies offer promising potential to develop high-efficiency thin-film solar cell at dramatically reduced cost. However, the lack of a cost effective scalable nanomanufacturing technique remains the main road-block. In nature, diatoms exhibit high solar energy harvesting efficiency due to their frustules (i.e., hard porous cell wall made of silica) possessing remarkable hierarchical nano-features optimized for the photosynthetic process through millions of years evolution. To explore this unique light trapping effect, different species of diatoms (Coscinodiscus sp. and Coscinodiscus wailesii) are cultured and characterized by Scanning electron microscope (SEM). Rigorous Coupled Wave Analysis (RCWA) and Finite-difference time-domain (FDTD) method are employed to numerically study the nanophotonic light-trapping effect. The absorption efficiency is significantly enhanced over the spectrum region centered on 450nm and 700nm where the electric fields are found strongly confined within the active layer. The transmission and reflection spectra are also measured by optical spectroscopy and the experimental results are in good agreement with numerical simulations.