Morphology Characterization of Bulk Heterojunction Solar Cells

Abstract

Revealing the nanostructure of bulk‐heterojunction (BHJ) photovoltaic blends is a critical task in the field of organic photovoltaics. The complicated morphology, ranging from binary blends to ternary mixtures, shows quite varied structural details that need to be fully characterized in terms of correlating them with device performance. The nonequilibrium nature of the BHJ thin‐film morphology makes the structure optimization difficult, and fundamental principles that relate to chemical structure, processing methods, and device performances have not yet been fully understood. On the other hand, various high‐powered techniques ranging from in‐house instrumentation to synchrotron techniques have been applied to this tremendously difficult research topic. More structural details, including length scale of phase separation, structural ordering, chain/molecular orientation, surface topology, etc., can be obtained in a quantitative manner, which finally allows the structure–property relationships to be determined. Here, the most important characterization techniques in understanding the morphology of BHJ solar cells are summarized, targeting chemists and materials scientists.

Two Well‐Compatible Acceptors with Efficient Energy Transfer Enable Ternary Organic Photovoltaics Exhibiting a 13.36% Efficiency

“…The similar phenomenon on phase separation degree variation can also be observed from TEM images of the binary and the ternary blend films, as exhibited in Figure c. The dark and bright regions in TEM image are normally assigned as acceptor‐rich and donor‐rich domain, respectively . No obvious characteristics can be observed from the TEM image of PM6:T6Me blend films.…”

“…The dark and bright regions in TEM image are normally assigned as acceptor-rich and donor-rich domain, respectively. [49][50][51] No obvious characteristics can be observed from the TEM image of PM6:T6Me blend films. The TEM image of PM6:IT-2F blend films displays the nanometer-scale dark and bright region with nanofibril structure.…”

Aggregation‐Induced Multilength Scaled Morphology Enabling 11.76% Efficiency in All‐Polymer Solar Cells Using Printing Fabrication

“…Average PCE that exceeds of 11.25% (11.76% maximum) is achieved for the first time in all‐PSC. Soft and hard X‐ray scattering techniques as well as microscopy methods are used to investigate the morphological details, from which we see that interaction parameter between polymers and solvents, the intermolecular interaction, solubility, and material crystallization are critical parameters that influence the final morphology and device performance of printed solar cells …”

As‐Cast Ternary Organic Solar Cells Based on an Asymmetric Side‐Chains Featured Acceptor with Reduced Voltage Loss and 14.0% Efficiency

“…PM6 donor in its thin film has a dominant face‐on orientation, with a broad (100) reflection in the in‐plane (IP) direction at 0.21 Å −1 and a π–π stacking peak in the out‐of‐plane (OOP) direction at 1.70 Å −1 . The crystal coherence lengths (CCLs) for (100) and (010) diffractions were 5.67 and 1.40 nm, respectively, estimated by the Scherrer Equation . The two acceptors both preferred face‐on orientations.…”

“…The crystal coherence lengths (CCLs) for (100) and (010) diffractions were 5.67 and 1.40 nm, respectively, estimated by the Scherrer Equation. [49] The two acceptors both preferred faceon orienta tions. TOBDT displays a quite different diffraction pattern, with (100) reflection in the IP direction at 0.27 Å −1 and (010) diffraction in the OOP direction at 1.79 Å −1 , showing CCLs of 6.78 and 1.99 nm, respectively.…”