Side-Chain Deuteration Enables High-Contrast Neutron Scattering of Solution Aggregates in Organic Photodiodes and Enhances Device Performance

Abstract

Understanding the solution-state aggregation of conjugated polymers is essential for controlling their film microstructure and improving optoelectronic device performance. However, resolving aggregate structures in donor:acceptor blends remains challenging due to limited contrast and the multicomponent nature of these systems. Here, we selectively deuterate the side chains of poly(3-hexylthiophene) (P3HT) to produce P3HT-D, substantially increasing its neutron scattering length density (SLD). This isotopic modification enables high-contrast small-angle neutron scattering (SANS) analysis of polymer aggregation in solutions of polymer:nonfullerene acceptor (NFA) blends. The enhanced contrast overcomes the deficiencies of conventional X-ray scattering and microscopy, allowing for unambiguous determination of chain conformation and aggregate structure. Photodiodes incorporating P3HT-D show improved responsivity and achieve a high specific detectivity of 5.67 × 1013 Jones. These improvements are attributed to refined film morphology, improved miscibility, and reduced nonradiative recombination facilitated by isotopic substitution. Our findings demonstrate that side-chain deuteration provides a dual benefit: (i) enabling precise structural characterization and (ii) tuning intermolecular interactions to improve device performance. This study establishes side-chain deuteration as a versatile strategy for structural analysis, microstructure engineering, and performance optimization in conjugated polymer–based organic photodiodes.