A novel stable bisazide molecule that can freeze the bulk heterojunction morphology at its optimized layout by specifically bonding to fullerenes is reported. The concept is demonstrated with various polymers: fullerene derivatives systems enable highly thermally stable polymer solar cells.

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The influence of fullerene side chain functionalization on both the morphology and electro-optical properties of bulk-heterojunction polymer:fullerene solar cells is discussed through a systematic investigation of material blends consisting of the conjugated polymer poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) as donor and fullerene molecules with different side chains as the acceptor. The varying side chain of the fullerenes was found to induce morphological changes as confirmed by different analytical techniques such as Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and Nuclear Magnetic Resonance (NMR). The fullerene with the shorter side chain, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), forms crystalline nanophases in the blend, while this is not the case for the alternative diphenylmethanofullerene acceptor, [6,6]-1,1-bis(4,4′-dodecyloxyphenyl)methanofullerene (DPM-12). The introduction of NMR allows us to estimate the fraction of crystalline fullerene. The morphological changes have a profound effect on the characteristics of charge transfer states (CT) formed at the polymer:fullerene interfaces. Crystallization of fullerene molecules shifts the energy of the CT state. This shift in energy is directly manifested in the open-circuit voltage of solar cells based on the fullerene acceptors under investigation.

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Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan–French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.

This article is devoted to the study of the photoaging and thermal aging of poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO–PPV; also called OC1C10–PPV) used in organic solar cells. Thin MDMO–PPV films (thickness < 1 μm) were exposed to ultraviolet‐light irradiation (λ > 300 nm) in the presence of air or thermooxidized at 60 °C. The modifications of the chemical structure of the matrix were analyzed with ultraviolet–visible and infrared spectroscopy. The oxidation products that formed were identified by postirradiation treatments, including chemical derivatization reactions. On the basis of the identification of the various products formed, a two‐step radical mechanism is proposed to account for the modification of the chemical structure of the polymeric matrix. It involves first the oxidation of the ether substituent followed by the oxidation of the double bonds. These reactions are responsible for a loss of conjugation of MDMO–PPV, chain scissions, and a decrease in the visible absorbance, which are anticipated to drastically impair the photovoltaic properties of the material. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 317–331, 2007

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