Using Neutron Spin Echo Resolved Grazing Incidence Scattering to Investigate Organic Solar Cell Materials

The overall goal of the following experiment is to demonstrate that neutrons spin, echo resolved grazing incident scattering. Suris can be used to probe the length scales present in irregular thin film samples such as the active layer within polymer solar cells. This is achieved by preparing suitable samples that have irregular structures as a second step.

The length scales of these structures are measured using conventional optical and atomic force microscopy techniques to confirm that irregular structures are present. Next neutron suris measurements are taken using the prepared samples. Results are obtained that show the length scales observed in the suris experiments match the results of conventional microscopy.

This demonstrates that neutrons spin echo resolved grazing incident scattering is capable of probing this type of sample. The main advantage of this technique over existing methods like scanning probe microscopy, which looks at the surface structure, is it should be able to probe structures inside the sample as well as on the surface. This method can help answer key questions in the polymer foot all tank field, such as how does the nanostructure inside the active layer of a polymer foot vol tank device influence their performance as shown in this schematic depiction.

The experiment begins by preparing two plasma clean silicon wafers. Spinco each wafer with pdot PSS to create a thin film. After drying, add a second layer to each coated substrate by spin.

Coating a prepared solution of P three HT PCBM. Set aside one sample and thermally an knee, the other sample for one hour at 150 degrees Celsius to grow crystal lights on the thin film surface with the an kneeling completed. Use an optical microscope to capture images of both samples.

Also make an atomic force microscope image of each sample to perform the experiments. Take the samples to a neutron beam line here ISIS. First select the sample to provide a reference polarization and align it on the positioning table of the neutron beam line.

Then align the two prepared samples on the table. After passing through the sample, the beam will continue to the end of the beam line here. After the analyzer, use a vertically oriented scintillator detector to collect data for the experiment.

With the samples in place, secure the beam line area. Continue with the experiment in the control room. Set up the off specular reflectometer to produce wavelengths from two angstroms to 14 angstroms, and tune the instrument to balance the total number of neutron processions in each arm of the instrument.

Collect data to check that the instrument is properly tuned. The tuning graph should show that all wavelengths of neutrons are treated equally. Next, set the angle of grazing incidents here, 0.3 degrees by tilting the sample table so that the neutron beam is incident upon the polarization reference sample.

Move the sample translation stage to place the polarization reference sample in the neutron beam. Use the scintillator detector to measure the scattered neutron intensity as a function of position for both spin up and spin down. After about one hour, translate the sample stage to measure the sample of interest.

Follow the same procedure to record neutron intensity for both spin up and spin down orientations alternate between the two samples at intervals of about one hour until sufficient data is obtained. The data consists of spin up and spin down 2D intensity maps for each sample, calculate the polarization P for each pixel in the data sets. Using this formula.

Here I up and I down are the spin up and spin down intensities respectively normalize the polarization for the sample of interest using the polarization of the reference sample data. The normalized polarization plot for the sample of interest can now be probed. Select a region of the plot for integration in this case between detector numbers one 10 and one 18 and obtain the sur correlation function.

Finally, plot the data to compensate for different scattering length densities at different wavelengths. The log of the normalized signals from both an as cast and an A kneeled sample are compared here as a function of the spin echo length in nanometers. The unneeded sample in red contained no structural correlations on the length scales that the measurement is sensitive to.

This explains the flat line at zero, which corresponds to a normalized polarization of one. The ene sample data in black starts at zero, but the polarization decays significantly as the spin echo length increases until a plateau is reached at 1, 200 nanometers. The data is consistent with a maximum average particle diameter of approximately 1, 200 nanometers.

If it is assumed that there are no near neighbors a reasonable assumption from previous microscopy measurements. S'S experiments are still very much in their infancy, but we expect this technique being used to probe varied structures within thin films in the near future.