If you were given a nickel for every time the solar industry promised a technology that would finally make solar power universal and cheap, then you would have, well, universal and cheap solar power by now. Alas, this is not the case, when ten countries account for 65.4% of the world’s 178 GW solar capacity. Furthermore, affordability is consistently challenged by high installation prices; the United States (the 5th-largest solar power consumer) boasts a $4.87-per-watt average installation cost that is over double that of coal and natural gas, giants of the American energy industry. But a new joint quantum physics and bioengineering effort spearheaded by Professors Seth Lloyd and Angela Belcher of MIT holds the potential to dramatically boost solar energy efficiency and radically transform how we see solar cells.
Most solar cell engineering advances in recent years have revolved around factors fundamental to materials science, such as catalysts, semiconductor junctions, and light concentrators. Lloyd and Belcher’s approach — though only an experimental proof of concept at this stage, not a full-fledged solar cell — instead addresses the scientific foundations of cell operation. Their novel method of harvesting light uses genetically-engineered viruses to optimize light transfer through a synthetic molecular structure inspired by plant pigments.
Currently, Soitec (a French electronics firm) and the Fraunhofer Institute for Solar Energy Systems (a German research society) hold the solar cell efficiency record of 46% of theoretical energy transfer. However, such cells are built (and priced) to go to outer space. The efficiency record for commercial solar cells pales in comparison at 22.1% for a Panasonic model. Neither of these systems, however, can hold a candle to the near-perfect efficiency of nature’s solar energy conversion system — photosynthesis.
Introductory biology explains light-dependent photosynthesis with a fairly straightforward reaction pathway. A chlorophyll molecule absorbs a visible light photon, releasing an electron that is transferred between several other molecules as it travels down an electron transport chain that facilitates the synthesis of ATP, thus storing chemical energy.
This picture can be adjusted to incorporate a quantum approach, with excitons — quasi-particles consisting of an electron bound to a valence state hole — taking the place of electrons. Under this explanation, photon absorption generates an exciton, which bounces from chromophore (the conjugated portion of a molecule responsible for color) to chromophore until it reaches a reaction center where ATP synthesis can occur. According to earlier research by Lloyd, further “quantum weirdness” effects hold the key to the remarkable efficiency of photosynthesis.
Quantum weirdness permits an individual particle (or quasi-particle) to exist in multiple states at one time — hence a single exciton can simultaneously explore multiple chromophore pathways to a reaction center. From this information, excitons can select the optimal least-time pathway, minimizing energy loss and attaining maximal efficiency — a process that Lloyd terms the “quantum Goldilocks effect.”
However, is it not technologically feasible to use biodegradable pigments to apply these phenomena to a solar cell. Instead, the MIT collaboration uses organic dyes, since colored compounds contain chromophore sites. The optimal chromophore spacing — the condition of the “Goldilocks effect” — is induced by grafting several dye molecules onto an M13 bacteriophage. Intriguingly, the M13 virus has already found uses in nanotechnology, including as a candidate for regulating carbon nanotubes in photovoltaic cells. The M13 virus is responsible for collecting the light energy, as a reaction center does in photosynthesis. The next logical step will be to harness this efficiently collected energy into power production. Though this quantum-optimized photosynthesis mimicry remains a fair distance from technological realization, its potential to alter efficiency benchmarks should elevate its trajectory as solar power exceeds 200 GW and 1% of global power production.