Recently, non-fullerene n-type organic semiconductors have attracted significant attention as acceptors in organic photovoltaics (OPVs) due to their great potential to realize high-power conversion efficiencies. The rational design of the central fused ring unit of these acceptor molecules is crucial to maximize device performance. Here, we report a new class of non-fullerene acceptor, Y6, that employs a ladder-type electron-deficient-core-based central fused ring (dithienothiophen[3.2-b]-pyrrolobenzothiadiazole) with a benzothiadiazole (BT) core to fine-tune its absorption and electron affinity. OPVs made from Y6 in conventional and inverted architectures each exhibited a high efficiency of 15.7%, measured in two separate labs. Inverted device structures were certified at Enli Tech Laboratory demonstrated an efficiency of 14.9%. We further observed that the Y6-based devices maintain a high efficiency of 13.6% with an active layer thickness of 300 nm. The electron-deficient-core-based fused ring reported in this work opens a new door in the molecular design of high-performance acceptors for OPVs.

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On the basis of theoretical models and calculations, several alternating polymeric structures have been investigated to develop optimized poly(2,7-carbazole) derivatives for solar cell applications. Selected low band gap alternating copolymers have been obtained via a Suzuki coupling reaction. A good correlation between DFT theoretical calculations performed on model compounds and the experimental HOMO, LUMO, and band gap energies of the corresponding polymers has been obtained. This study reveals that the alternating copolymer HOMO energy level is mainly fixed by the carbazole moiety, whereas the LUMO energy level is mainly related to the nature of the electron-withdrawing comonomer. However, solar cell performances are not solely driven by the energy levels of the materials. Clearly, the molecular weight and the overall organization of the polymers are other important key parameters to consider when developing new polymers for solar cells. Preliminary measurements have revealed hole mobilities of about 1 x 10(-3) cm2 x V(-1) x s(-1) and a power conversion efficiency (PCE) up to 3.6%. Further improvements are anticipated through a rational design of new symmetric low band gap poly(2,7-carbazole) derivatives.

Harvesting energy directly from sunlight using photovoltaic cells (PCs) is a very important way to address growing global energy needs with a renewable resource while minimizing detrimental effects on the environment. For this purpose, the development of polymeric solar cells has received a great deal of attention from both academic and industrial laboratories. [1][2][3] Indeed, the utilization of semiconducting conjugated polymers as active components in bulk heterojunction photovoltaic devices offers significant potential advantages over existing inorganic materials in terms of ease of processing, formation of large surface areas, and costs. For example, poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-p-phenylenevinylene] (MDMO-PPV), [4] regioregular poly(3-hexylthiophene) (P3HT), [5,6] and other polythiophene derivatives [7] have been extensively studied over the last decade, resulting in PCs with a power conversion efficiency between 3.0 and 5.0 %. However, the performances of these polymers are somehow restricted by their relatively large bandgap and the limited possibilities to modulate their physical properties by synthetic methods. New low-bandgap polymers have been developed over the years to better harvest the solar spectrum, especially in the 1.4-1.9 eV region. Promising copolymers based on fluorene units have been proposed by Andersson/Inganäs [8,9] and Cao, [10] with power conversion efficiencies between 2.0 and 2.8 %. Interestingly, the physical properties of polyfluorene derivatives can be easily modulated through the design of various alternating copolymers.[11] However, relatively low hole mobilities were reported for low-bandgap polyfluorene derivatives. Therefore, besides those recent advances, there is still a need for new polymeric materials to go beyond the 5 % efficiency of actual materials. [3,12,13] Along these lines, poly(N-vinylcarbazole) (PVK) is well known as an excellent photoconductor. [14,15] Furthermore, studies have demonstrated that PVK photoconduction increases when doped with sensitizers like 2,4,7-trinitrofluorenone (TNF) or C 60 . [15,16] In parallel, oligo-and poly(2,7-carbazole) derivatives have been successfully used in polymer lightemitting diodes (PLEDs) [17] and organic field-effect transistors (OFETs), [17,18] demonstrating good p-type transport properties. Recently, Müllen and co-workers [19] have reported solar cells with an efficiency of 0.6 % with poly(N-alkyl-2,7-carbazole), whereas Leclerc and co-workers [20] have shown an efficiency of 0.8 % with poly(2,7-carbazolenevinylene) derivatives. Moreover, in contrast with the fluorene unit the carbazole moiety is fully aromatic, providing a better chemical and environmental stability. Taking all of these results into account, the development of new low-bandgap copolymers based on carbazoles should therefore lead to interesting features for photovoltaic applications. However, poly(N-alkyl-2,7-carbazole)s generally exhibit poor solubilities and low molecular weights. [21] To solve these problems, bulky side chains are us...

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A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap (1.73 eV) and a deep highest occupied molecular orbital energy level (5.57 eV). The introduction of branched alkyl chains to the dithienosilole unit was found to be critical for the improvement of the polymer solubility. When blended with PC(71)BM, PDTSTPD exhibited a power conversion efficiency of 7.3% on the photovoltaic devices with an active area of 1 cm(2).

Over the last five years, organic photovoltaic devices have emerged as a new competitor to siliconbased solar cells. In particular, the bulk heterojunction architecture (BHJ), in which the photoactive layer consists of a bicontinuous blend of an electron donor and an electron acceptor, has allowed power conversion efficiencies around 8%. We will present in this review the latest conjugated polymers used in such BHJ solar cells. We will mainly focus on electron-donating (p-type) polymers based on thiophenes, 1,3,2-benzodiathiazoles, pyrrolo[3,4-c]pyrrole-1,4-diones, benzo[1,2-b;3,4-b]dithiophenes, and few other materials with more exotic structures. This review should be helpful to evaluate which are the most promising materials and where this research field is going in the years to come.

Different electrostatic interactions and conformational structures between single‐ or double‐stranded negatively charged nucleic acids bound to a surface (see picture) and water‐soluble cationic poly(3‐alkoxy‐4‐methylthiophene) derivatives (in yellow) provide the basis for a sensitive optical detection method (colorimetric or fluorometric) for oligonucleotide hybridization.