Polymer-based solar cells are attractive to solar energy developers because they are inexpensive and relatively easy to fabricate. But to be economically viable, they must be made more efficient. Neutron scattering measurements have shown that appropriately heat-treating (annealing) a thin film containing a blend of the polymers PSBTBT and PCBM causes the polymers to distribute and mix in a way that improves the efficiency of the device. The experiments showed that the film reached its maximum power conversion efficiency when annealed for one minute at 150 degrees Celsius after aluminum electrodes were deposited on the film. Conversely, annealing before the electrodes were deposited reduced the efficiency of the film. The neutron scattering experiments were conducted at the High Flux Isotope Reactor and the Spallation Neutron Source, both at Oak Ridge National Laboratory. The results are important to improving the performance of polymer-based solar cells.
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