Doan Vu

Self‐doped conjugated polyelectrolytes (CPEs) offer a unique combination of π‐conjugated backbones and ionic side chains, enabling solution‐processability, mixed ionic‐electronic conductivity, and applications in aqueous environments. However, their high water solubility hinders long‐term stability, necessitating effective cross‐linking strategies. Here, we systematically investigate ionic cross‐linking of the benchmark p‐type self‐doped poly[2,6‐(4,4‐bis‐potassium butanylsulfonate‐4H‐cyclopenta‐[2,1‐b;3,4‐b′]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)], CPE‐K, using a post‐deposition approach with divalent cations (Mg ^{2 +} , Ca ^{2 +} , Sr ^{2 +} , Ba ^{2 +} ). Thin films immersed in aqueous salt solutions exhibit complete ion exchange, as confirmed by XPS. AFM and liquid‐mode AFM reveal that swelling suppression and morphological stability depend strongly on the cation identity and concentration, with Ba ^{2 +} forming the most rigid cross‐linking network. GIWAXS shows that ionic cross‐linking expands lamellar spacing while preserving π – π stacking. Electronic conductivity measurements demonstrate that Ba ^{2 +} ‐treated films maintain high conductivity in the swollen state due to improved network integrity. Impedance spectroscopy further shows decreasing ionic conductivity with increasing cross‐linking density. These findings establish structure–property relationships for ionic cross‐linking in CPEs and provide design insights into processing protocols to form robust CPE films caste from water.

The thermal transitions of organic semiconductors have important implications for morphological and thermomechanical properties of electronic devices. Here we show that in situ UV–vis spectroscopy coupled with automated data analysis is a facile tool to determine the numerous thermal transitions that can exist in organic semiconductor thin films. Thermal transitions are automatically identified through employing linear segment detection of the semilogarithmic normalized deviation metric (NDM) as well as the spectral changes using piecewise linear regression. Furthermore, by comparing the in situ UV–vis with other thermal measurement methods we observe the temperature dependent absorbance can be used to discern the type of thermal transitions including liquid crystal transitions, glass transitions, and melting temperatures. This approach is used to characterize five well‐known conjugated polymers and a small molecule semiconductor, each with distinct thermal phase behavior, where we show good agreement with other thermal characterization methods. Thus, the method we introduce, which we refer to as A utomated T hermal transition identification using L inear regression analysis of the A bsorbance S pectra (ATLAS), is shown to be an effective and simple screening tool to identify multiple thermal transitions in thin films. This is a high‐throughput thermal analysis approach that will assist in advancing structure‐morphology‐function relations in organic electronics.

A Hansen solubility parameter-guided framework is introduced for decoupling side chain–solvent and backbone–solvent interactions for control of polymorphism and orientation in conjugated polymer thin films.

Adding a thermoplastic elastomer to an organic solar cell (OSC) active layer has been shown to improve its mechanical resilience while largely maintaining the optoelectronic performance. However, a guide to select from the many available elastomers is needed for systematic optimization. Here, we delineate how the structure and composition of the elastomer impact the active layer morphology, fracture toughness, and OSC performance when applied in a high-efficiency polymer/small-molecule acceptor active layer. We compare styrene-ethylene-butylene-styrene (SEBS) and styrene-ethylene-propylene-styrene (SEPS) elastomers with varying molecular weight (M_w) and styrene content. The morphology was probed in detail by resonant soft X-ray scattering (RSoXS) and grazing incidence wide angle X-ray scattering (GIWAXS). We reveal that the compliant elastomer is more impactful than M_w in improving the fracture toughness. The compliance increases when the styrene content is reduced and when the EP block is employed instead of the EB block. In addition, the improved miscibility of the low-styrene-content SEPS leads to the least disruption of the molecular packing, resulting in maintaining power conversion efficiency (PCE) the best. These factors lead to the emergence of a Pareto front along the fracture toughness and OSC efficiency dimensions. The optimal combination of mechanical resilience and OSC efficiency was found when incorporating a mass fraction of 7.5% low-styrene-content SEPS in a PM6/BTP-eC9 active layer. Such OSCs maintained nearly 95% of the neat binary active layer PCE while more than tripling the fracture energy. Based on these results, guidelines for elastomer selection and loading are provided to advance rubber-toughened OSCs.