National Renewable Energy Laboratory (NREL) Research Scientist Bryon Larson, as part of an international research team, achieved a record-breaking 18.07% power conversion efficiency from an organic photovoltaic (OPV) solar cell – or as such materials are better known: Plastic.
Historically, OPV cells have mostly improved through an iterative process.
However, Larson and his collaborators have hit upon an “aha!” moment with a new design strategy that simultaneously improves the cell’s open-circuit voltage, short-circuits voltage, and fill factor.
Concurrently improving all three of these primary metrics – which represent how efficiently a solar cell converts sunlight into electricity – is difficult due to the traditional constraints of only using two components to create the binary donor-acceptor blend in an OPV cell’s light-absorbing layer.
Changing a single component to improve one metric can negatively affect another, leading to performance trade-offs.
“The name of the game for advancing OPV is new materials,” Larson said. “But because of the way that OPVs work, every time you introduce new material into the absorber blend, you have to reoptimize everything about the cell design. It’s a time-consuming, haphazard process, like trying to find a needle in a haystack. Our strategy demonstrates a quaternary, four-component, approach where each component works in synergy to avoid performance trade-offs and to produce a high power conversion efficiency.”
The absorber layer in an OPV cell is responsible for light absorption, exciton splitting to generate positive and negative charges, and effective transport of charges to the contacts to produce photocurrent.
The design of a traditional OPV cell struggles to balance the electronic and morphological characteristics of just two sets of molecules or polymers for all these functions.
Larson, working with researchers from Shanghai Jiao Tong University and the University of Massachusetts Amherst, showed that using four components in an OPV device’s active layer could better balance the microstructure and electronic function of the cell’s absorber layer.
This holistic strategy is described in the Nature Communications article “Single-layered organic photovoltaics with double cascading charge transport pathways: 18% efficiencies.”
Organic photovoltaic devices (OPV) use a unique process to convert sunlight into electricity. This graphic depicts a cross-section of an OPV device that has an active layer only 100 nanometers thick and explains the basic operating physics that are unique to OPV. Their low cost and flexible form factor could enable new applications for solar energy. Image by Bryon Larson, NREL