Quantitative Tomography of Organic Photovoltaic Blends at the Nanoscale

Abstract

The success of semiconducting organic materials has enabled green technologies for electronics, lighting, and photovoltaics. However, when blended together, these materials have also raised novel fundamental questions with respect to electronic, optical, and thermodynamic properties. This is particularly important for organic photovoltaic cells based on the bulk heterojunction. Here, the distribution of nanoscale domains plays a crucial role depending on the specific device structure. Hence, correlation of the aforementioned properties requires 3D nanoscale imaging of materials domains, which are embedded in a multilayer device. Such visualization has so far been elusive due to lack of contrast, insufficient signal, or resolution limits. In this Letter, we introduce spectral scanning transmission electron tomography for reconstruction of entire volume plasmon spectra from rod-shaped specimens. We provide 3D structural correlations and compositional mapping at a resolution of approximately 7 nm within advanced organic photovoltaic tandem cells. Novel insights that are obtained from quantitative 3D analyses reveal that efficiency loss upon thermal annealing can be attributed to subtle, fundamental blend properties. These results are invaluable in guiding the design and optimization of future devices in plastic electronics applications and provide an empirical basis for modeling and simulation of organic solar cells.

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

“…Thereby, peaks are fitted by Lorentzian model functions to determine the center position. [43] The plasmon peak map for the as-casted blend in Figure 2b reveals that very small to medium-sized (3-50 nm) fullerene-enriched domains are present in blends processed with DIO. Using spatially resolved low-energy-loss spectra, a segmentation of the domains into wileyonlinelibrary.com different material classes was carried out, enabling also identification of enriched and mixed phases.…”

Square‐Centimeter‐Sized High‐Efficiency Polymer Solar Cells: How the Processing Atmosphere and Film Quality Influence Performance at Large Scale

“…Maps of peak positions reveal the compositional variations between polymer, mixed, and fullerene phases at high spatial resolution. [40] In Figure 4, we compare maps of plasmon peak positions from STEM-SI experiments of PTB7-Th:PC 71 BM blends of 1:1.5 and 1.2 ratios with a PTB7:PC 71 BM blend of optimal 1:1.5 ratio. It can be seen that in the case of PTB7-Th:PC 71 BM using a mass ratio 1:1.5, the domain sizes of both donor and acceptor phases are very small (Figure 4a) compared to PTB7:PC 71 BM with the identical mass ratio (Figure 4c).…”

Efficient and Versatile Interconnection Layer by Solvent Treatment of PEDOT:PSS Interlayer for Air‐Processed Organic Tandem Solar Cells

“…Two different donor materials were used for the tandem device: a high band gap polymer, HBG1 (provided by Merck), for the bottom cell, and a low band gap polymer, PMDPP3T, for the top layer. The absorption spectra of the resulting polymer:fullerene blends are reported in Figure a.…”