6 Feb 2018
Determining the efficacy of organic solar cell mixtures is a time-consuming and tired practice, relying on post-manufacturing analysis to find the most effective combination of materials.
Now, an international group of researchers – from North Carolina State University in the US and Hong Kong University of Science and Technology – have developed a new quantitative approach that can identify effective mixtures quickly and before the cell goes through production.
By using the solubility limit of a system as a parameter, the group looked to find the processing temperature providing the optimum performance and largest processing window for the system, said Harald Ade, co-corresponding author and Professor of Physics at NC State.
‘Forces between molecules within a solar cell’s layers govern how much they will mix – if they are very interactive they will mix but if they are repulsive they won’t,’ he said. ‘Efficient solar cells are a delicate balance. If the domains mix too much or too little, the charges can’t separate or be harvested effectively.’
‘We know that attraction and repulsion depend on temperature, much like sugar dissolving in coffee – the saturation, or maximum mixing of the sugar with the coffee, improves as the temperature increases. We figured out the saturation level of the ‘sugar in the coffee’ as a function of temperature,’ he said.
Organic solar cells are a type of photovoltaic – which convert energy from the sun into electrons – that uses organic electronics to generate electricity. This type of cell can be produced cheaply, and is both lightweight and flexible, making it a popular option for use in solar panels.
However, difficulties in the production process, including an effective process to determine efficiency of potential material combinations, is stalling its development.
‘In the past, people mainly studied this parameter in systems at room temperature using crude approximations,’ said Long Ye, first author and postdoctoral researcher at NC State. ‘They couldn’t measure it with precision and at temperatures corresponding to processing conditions, which are much hotter.’
‘The ability to measure and model this parameter will also offer valuable lessons about processing and not just material pairs.’
But the process still needs refinement, said Ade. ‘Our 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,’ he said.
Nature Materials, DOI: 10.1038/s41563-017-0005-1
By Georgina Hines