From a morphological perspective, the understanding of the influence of the [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) content on the morphology of the active layer is not complete in organic solar cells (OSCs) with bulk heterojunction (BHJ) configuration based on the low-bandgap polymer poly­[4,8-bis­(5-(2-ethylhexyl)­thiophen-2-yl)­benzo­[1,2-b;4,5-b′]­dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno­[3,4-b]­thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th). In this work, we obtain the highest power conversion efficiency (PCE) of 10.5% for BHJ organic solar cells (OSCs) with a PTB7-Th/PC71BM weight ratio of 1:1.5. To understand the differences in PCEs caused by the PC71BM content, we investigate the morphology of PTB7-Th/PC71BM blend films in detail by determining the domain sizes, the polymer crystal structure, optical properties, and vertical composition as a function of the PC71BM concentration. The surface morphology is examined with atomic force microscopy, and the inner film morphology is probed with grazing incidence small-angle X-ray scattering. The PTB7-Th crystal structure is characterized with grazing incidence wide-angle X-ray scattering and UV/vis spectroscopy. X-ray reflectivity is employed to yield information about the film vertical composition. The results show that in PTB7-Th/PC71BM blend films, the increase of PC71BM content leads to an enhanced microphase separation and a decreased polymer crystallinity. Moreover, a high PC71BM concentration is found to decrease the polymer domain sizes and crystal sizes and to promote polymer conjugation length and formation of fullerene-rich and/or polymer-rich layers. The differences in photovoltaic performance are well explained by these findings.

In (S)TEM the energy dispersive X-rays spectroscopy (EDS) is used for compositional analysis with high lateral resolution. The accuracy of the quantification result is crucial for the understanding of the materials properties. A key advantage of ζ-factor quantification method [1] discussed in this contribution compared to the more commonly used Cliff-Lorimer quantification is that the sample thickness does not need to be determined for the quantification, but that it can be derived from the easier accessible beamcurrent used in the experiment. On the other hand some systematic errors do not cancel out in the ζ-factor method whereas they do in Cliff-Lorimer quantification. The EDS live time, effective solid-angle and beam current have to be measured with high accuracy. Even though the theory is established [2], an overview of these systematic errors on the field of the ζ-factor is missing.In this work, an investigation on the reproducibility of the ζ-factor among different experimental conditions is presented. EDS spectra are acquired under variation of several parameters like: beam current, size of the illuminated area, position on the sample, tilting angle, apertures settings, beam voltage, sample compound, and on different machines. For a proper ζ-factor calibration, an accurate measure of the beam current and a sample with known thickness is required. The beam current read out from the flu screen can be influenced by several effects: e.g. inhomogeneity, charging, non-linearity. In order to validate the flu-screen read out, a sample holder with integrated Faraday cup is used. The sample used is a Si3N4 amorphous film with 200nm thickness, which is produced using lithography techniques to have a well-defined thickness and homogeneous thickness. The Si3N4 film is deposited on a silicon waver and afterwards the waver is etched away on the backside of the film to make the sample electron transparent. Figure 1 shows machine-to-machine reproducibility of the ζ-factor at 200 and 300kV. Measurements were performed in the factory, following a routine protocol on the machine before shipment. The 200kV results show a good reproducibility across the tools. For the 200nm thick Si3N4 sample an error in the thickness estimate of %10, results in a quantification error of 1.6 at% at zero tilt. So even with the 17% variation of zeta-factors at 300 kV, a quantification error of less than 3 at% is expected. Cliff-Lorimer quantification would give an error of 14 at%.An estimation of the uncertainty of the ζ-factor value relative to different sources is reported. The sources of uncertainty using different tools are further investigated.. Nevertheless the stability of both the sample and the system were investigated by a 60-hour continuous EDS acquisition. Figure 2 shows that the system stability is excellent. Additionally model-based correction of the effect of holder shadowing on the effective solid-angle is discussed in the ζ-factor measurements of this contribution [3]. It is shown a single zeta-factor can be used across machine...