Nanoscale Chain Alignment and Morphology in All-Polymer Blends Visualized Using 2D Polarization Fluorescence Imaging: Correlation to Power Conversion Efficiencies in Solar Cells

Abstract

All-polymer blends are promising materials for organic electronics. Their performance critically depends on the quality of mixing of the electron donor and acceptor polymers and on the local chain organization. We investigated spatially resolved photoluminescence properties of as-prepared and annealed blends of poly­[2,3-bis­(3-octyloxyphenyl)­quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and poly­(N,N-bis-2-octyldodecyl-naphtalene-1,4,5,8-bisdicarboximide-2,6-diyl-alt-5,5–2,2-bithiophene) (N2200) using two-dimensional polarization imaging (2D POLIM). N2200 is known to aggregate into fiber-like morphologies with a few hundreds of nanometers lateral extensions. Our findings suggest a highly parallel chain organization within individual domains. Comparing blends differing in the batch of the N2200 component, we could relate decreased power conversion efficiencies of the corresponding devices to aggregation of N2200 in tens of micrometer-sized elongated structures. TQ1 showed less sensitivity to preparation conditions. Other than N2200, TQ1 is liquid crystalline, and its side chain structure hinders aggregation. It thus might be feasible to consider similar properties for the design of acceptor polymers as well.

Recent Advances, Design Guidelines, and Prospects of All-Polymer Solar Cells

“…This situation strongly necessitates the development of new morphological characterization tools, which can enhance the contrast between different polymer domains. In this context, several recent studies demonstrated the effectiveness of utilizing a series of other imaging tools including photoinduced force microscopy (PiFM), conductive atomic force microscopy (c-AFM), Kelvin probe force microscopy (KPFM), , and two-dimensional polarization imaging (2D POLIM) . The simultaneous application of multiple complementary approaches (e.g., X-ray scattering and imaging tools) can provide more detailed and more extensive morphological information on all-PSC blends across different length scales (from micro to nanometer scale).…”

A review of non-fullerene polymer solar cells: from device physics to morphology control

“…One promising direction of molecular engineering is the design of conjugated materials having different sidechains to impart improved structural properties. It has been seen that the addi tion of a rigid sidechains along a conjugated backbone can impart favorable phase separation and miscibility properties [60,181]. There are also many studies that support the notion that the addition of methylated, fluorinated or alkylated side chains to ITIC can improve its deviceapplicable characteris tics [78,88,178,[182][183][184][185].…”

Nanofiber‐Directed Anisotropic Self‐Assembly of CdSe–CdS Quantum Rods for Linearly Polarized Light Emission Evidenced by Quantum Rod Orientation Microscopy

“…This could be exploited to image structures or dynamic properties of soft materials receiving much attention recently, or biological materials. The polarization of emission has been used in the case of 2D polarization microscopy, defocused microscopy of single molecules, or microscopy of scattering of gold nanorods . The combination of polarized emission from nanorods and weak supramolecular interactions involving organic capping of QRs is evaluated as an imaging technique for the first time in this work.…”