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Dynamic windows allow monitoring of in-door solar radiation and thus improve user comfort and energy efficiency in buildings and vehicles. Existing technologies are, however, hampered by limitations in switching speed, energy efficiency, user control, or production costs. Here, we introduce a new concept for self-powered switchable glazing that combines a nematic liquid crystal, as an electro-optic active layer, with an organic photovoltaic material. The latter aligns the liquid crystal molecules and generates, under illumination, an electric field that changes the molecular orientation and thereby the device transmittance in the visible and near-infrared region. Small-area devices can be switched from clear to dark in hundreds of milliseconds without an external power supply. The drop in transmittance can be adjusted using a variable resistor and is shown to be reversible and stable for more than 5 h. First solution-processed large-area (15 cm2) devices are presented, and prospects for smart window applications are discussed.

The rise of halogenated organic semiconducting materials has led to a significant increase of organic photovoltaic power conversion efficiencies in recent years. However, the impact of halogen atoms on optoelectronic, structural, and photovoltaic properties is not yet fully understood. In particular, because of different physicochemical properties, the design of polymers using chlorine atoms instead of fluorine atoms still needs to be rationalized. In this paper, we investigate a series of 4 halogenated D–A electron donor copolymers, by varying not only the number of halogen atoms, but also their nature. The in-depth experimental and theoretical study of these new polymers, using the nonhalogenated polymer as a reference, allowed us to rationalize the impact of these chemical modifications. In particular, we found that the structural properties and blending morphologies are mainly influenced by the nature of the halogen in this series of polymers. We have also demonstrated that a reasonable reduction in the number of fluorine atoms along the polymer backbone can be a good strategy to improve thin film processing conditions while keeping efficiencies at an acceptable level.

Diketopyrrolopyrrole (DPP) derivatives are among the most efficient materials studied for both polymer solar cells (PSCs) and organic field-effect transistors (OFETs) applications. We report here the synthesis of new fluorinated dithienyldiketopyrrolopyrrole (fDT-DPP) monomers suitable for direct heteroarylation polymerization. fDT-DPP copolymers were then prepared to probe the effect of the fluorination. It was found that they feature deeper HOMO energy levels and smaller bandgaps than their non-fluorinated analogues. Moreover, some fDT-DPP copolymers show ambipolar behavior when tested in OFETs. For example, P2shows hole mobility up to 0.8 cm2V–1s–1and electron mobility up to 0.5 cm2V–1s–1. Inverted PSCs with power conversion efficiency (PCE) up to 7.5% were also obtained for P5. These results reported here (OFETs and PSCs) confirm that the fluorination of dithienyl-DPP moieties improves the performance of organic electronics devices. This study is also evidencing the strength of the direct heteroarylation polymerization and fDT-DPP as a new class of conjugated polymers.