Fig. 2.

Basic electrochemistry and energetics of the photosynthetic solar cell, after ref. [4]. A chlorophyll molecule is connected to a reservoir at ambient temperature T ~ 300 K, and emitting heat at a rate I _qout, is excited due to the heat flow I _qin from the solar reservoir at temperature T = 5800 K, with a rate g to an excited state separated by an energy ην ₀ from the ground state. The excited chlorophyll state either decays with loss rate 1/τ or produces an electron–hole pair with net charge separation rate I and free energy Δμ = μ _e − μ _h