Designing artificial light harvesters with antennas

Biological light harvesting systems often feature antennas connecting the reaction centers. This maximizes light absorption but only if efficient energy transport pathways through the antennas exist. In a new paper, functional antennas are included in a model of an artificial light harvesting system, such as one in a solar cell. If energy transport in this model occurs via the quantum effect of adiabatic passage between states, the conversion of incoming light into internal energy is significantly enhanced in certain situations.

The model studied involves three molecules: a donor, a bridge molecule functioning as an antenna, and an acceptor molecule that produces product. The authors explicitly take the donor ground state into account, which has not been commonly done in previous studies. This introduces another quantum effect that can be used to design efficient energy transport networks.

The investigators considered four excitation schemes. In the first scheme, a continuous wave of laser light was used to excite the donor molecule. The second scheme considered a laser pulse, often used in ultrafast optical experiments. In the third scheme, incoherent light was considered. This situation mimics the natural situation for both photosynthesis and the normal working environment of a solar cell. The fourth scheme ignored the donor ground state and was used to benchmark the other schemes in which the ground state was included.

Significant enhancement in product formation was observed for the second scheme, where pulsed excitation was used. The investigators also found product formation with incoherent light does not strongly depend on bridge energy. These results are promising, and the authors propose future studies to include vibronic and other effects.

Source: “Efficient long-distance energy transport in molecular systems through adiabatic passage,” by Arend G. Dijkstra and Almut Beige, The Journal of Chemical Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5100210 .