Molecular doping of conjugated polymers is extremely desirable to control charge density gradients and shape the electric field across polymer electronic devices, including highly efficient organic solar cells. It is also a fundamental requirement for organic thermoelectrics and a powerful strategy to boost charge injection and transport properties in transistors. Yet, currently available doping approaches are far from offering a suitable level of control, particularly in the case of n-type doping. We here reveal that part of this limitation lies in the lack of understanding of dominant factors in doping efficiency. In particular, we highlight the key role played by very small amounts of a specific decomposition product formed during processing of the widely used molecular dopant 4-(2,3-dihydro-1,3dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (DMBI-H) in influencing the n-type conductivity in polymer blends. We show that such an overlooked decomposition product acts as a nucleating agent for a new crystalline phase of DMBI-H, with the overall effect of boosting the electrical conductivity of the final doped polymer films. Such results, confirmed by control experiments performed with a different nucleating agent, focus on the crucial role played by the solid-state microstructure in molecular doped semiconductors and offer ground for a significant change in design guidelines for molecular doping strategies.

The photon upconversion based on sensitized triplet−triplet annihilation (sTTA-UC) is a spin-flip mechanism exploited to recover the energy stored on dark triplet states in conjugated systems. In this process, a high-energy fluorescent singlet is created through the collision and fusion of two low-energy triplets belonging to different diffusing molecules. Its high yield in solution under low excitation intensity and noncoherent light highlighted the huge potential of sTTA-UC to provide a breakthrough in solar technologies. However, its diffusion-limited nature restrains its efficiency in the solid state. To overcome this issue, we propose a single-molecule system that is able to host simultaneously more than one triplet, thus enabling a diffusion-free intramolecular TTA. We obtain the first direct demonstration of intramolecular triplet fusion by tailored photoluminescence spectroscopy experiments, thus opening the way to realize a new family of single-molecule upconverters with huge potential in solar and lighting technologies by accessing the natural triplets' energy reservoir.

Carrying out photoredox direct arylation couplings between aryl halides and aryls in water solution of surfactants enables unprecedented selectivity with respect to the competing dehalogenation process, thanks to the partition...

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Molecular doping can increase conductivity of organic semiconductors and plays an increasingly important role in emerging and established plastic electronics applications. 1,3-Dimethyl-2-(4-(dimethylamino)phenyl)-2,4-dihydro-1H-benzoimidazole (N-DMBI-H) and tris(pentafluorophenyl)borane (BCF) are established n- and...

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Engineering the molecular structure of conjugated polymers is key to advance the field of organic electronics. In this work, we synthesized a molecularly encapsulated version of the naphthalene diimide bithiophene co-polymer PNDIT2, which is among the most popular high charge mobility organic semiconductors in n-type field-effect transistors, and non-fullerene acceptors in organic photovoltaic blends. The encapsulating macrocycles shield the bithiophene units, while leaving the naphthalene diimide units available for intermolecular interactions. With respect to PNDIT2, the encapsulated counterpart displays increased backbone planarity. Molecular encapsulation prevents pre-aggregation of the polymer chains in common organic solvents, while it permits π-stacking in the solid-state and promotes thin film crystallinity through an intermolecular-lock mechanism. Consequently, n-type semiconducting behavior is retained in field-effect transistors, although charge mobility is lower than in PNDIT2, due to the absence of the fibrillar microstructure that originates from pre-aggregation in solution. Hence, molecularly encapsulating conjugated polymers represents a promising chemical strategy in order to tune molecular interaction in solution and the backbone conformation, and to consequently control the nanomorphology of casted films, without altering the electronic structure of the core polymer.

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