Finding the most efficient mixture of materials for organic solar cells is presently limited to a rather trial and error approach, as chemists analyze how the donor and acceptor molecules within the solar cell mix and interact on an already manufactured cell.
Looking for a shortcut towards achieving the right cell mixtures, researchers at the North Carolina State University and the Hong Kong University of Science and Technology have developed a new quantitative relation that can identify the most promising material combinations in organic solar cells, determining at what temperature two separate materials turn into one homogenous mixture.
Aware that attraction and repulsion at the molecular level depends on temperature, the researchers were utilizing secondary ion mass spectrometry and X-ray microscopy to look at molecular interactions at different temperatures, and to see when the phase change occurred.
X-ray scattering allowed them to examine the purity of the domains. The end result was a parameter and quantitative model that describes domain mixing as a function of temperature, and that can be used to evaluate different mixtures.
“This parameter gives chemists the solubility limit of the system, which will allow them to determine which processing temperature will give optimum performance with the largest processing window,” says Harald Ade, professor at NC State and corresponding author of the paper.
In addition to material pairs, the research, titled Quantitative relations between interaction parameter, miscibility and function in organic solar cells, published in scientific journal Nature Materials, offers an insight into optimal processing conditions.
“In principle, our method can do this for a given organic mixture at any temperature during the manufacturing process,” says first author, Long Ye from NC State.
The researcher says that the ultimate goal is to form a framework and experimental basis on which chemical structural variation might be evaluated by simulations on the computer, before laborious synthesis is attempted.