Photosynthetic reaction center proteins evolved some 3.5 billion years ago to become extremely efficient light energy converters. They catalyze the most efficient early steps of the photosynthetic process that consist of the absorption and the conversion of light energy to electrical potential. Reaction centers such as photosystem I (PS I) are membrane protein-chlorophyll complexes. PSI functions like photodiode converting light quanta to electrical charges at quantum efficiency of ~100%, which is by far higher than any semiconductor photodiode. The high absorption cross section, the high quantum efficiency and the nano size dimensions make PS I a good candidate for use in hybrid protein-solids optoelectronic devices.