By controlling how the ‘mixing’ occurs between acceptor and donor layers (solar cell domains) in polymer-based solar cells, efficiency could be greatly boosted, says new research from a team that includes physicists from North Carolina State University.
This new research has given some insight into the most inner workings of these polymer-based solar cells, potentially leading to other future increases in efficiency.
In polymer-based solar cells, there are two domains, the acceptor, and the donor layers. The energy particles that are created by solar cells, excitons, need to be able to move quickly to the “interface of the donor and acceptor domains” for them to be used as an energy source.
It had been previously believed among researchers that making the “donor and acceptor layers as pure as possible was the best way to ensure that the excitons could travel unimpeded,” assuming that in this way solar cells would capture the most energy that they could.
But in the new research it was discovered that some mixing occurring between the two domains was not at all a negative thing. “In fact, if the morphology, or structure, of the mixed domains is small, the solar cell can still be quite efficient.”
North Carolina State physicist Harald Ade says: “We had previously found that the domains in these solar cells weren’t pure. So we looked at how additives affected the production of these cells. When you manufacture the cell, the relative rate of evaporation of the solvents and additives determines how the active layer forms and the donor and acceptor mix. Ideally, you want the solvent to evaporate slowly enough so that the materials have time to separate — otherwise the layers ‘gum up’ and lower the cell’s efficiency. We utilized an additive that slowed evaporation. This controlled the mixing and domain size of the active layer, and the portions that mixed were small.”
These mixed layers ended up having very good efficiency, leading to some thoughts that maybe allowing some mixing of the two layers wasn’t a problem, as long as the domains are small.
“We’re looking for the perfect mix here, both in terms of the solvents and additives we might use in order to manufacture polymer-based solar cells, and in terms of the physical mixing of the domains and how that may affect efficiency,” Ade says.
The findings are being published this month in two different journals, Advanced Energy Materials and Advanced Materials.
Source: North Carolina State University
Image Credit: Brian Collins, copyright Wiley
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