Synthesis of Functionalized γ‑Lactone via Sakurai <i>exo</i>-Cyclization/Rearrangement of 3,3-Bis(silyl) Enol Ester with a Tethered Acetal

An efficient synthesis of functionalized γ-lactones has been developed involving Sakurai <i>exo</i>-cyclization/rearrangement of 3,3-bis­(silyl) enol esters with a tethered acetal. While the steric and electronic effects of geminal bis­(silane) favor the desired Sakurai pathway, the methoxy species formed in the deprotection step also facilitates both cyclization and rearrangement. The synthetic value of this approach has been demonstrated by efficiently transforming the <i>E</i>-vinylsilane into enyne and the γ-lactone moiety into multisubstituted THF

Morphological Stability and Performance of Polymer–Fullerene Solar Cells under Thermal Stress: The Impact of Photoinduced PC₆₀BM Oligomerization

We report a general light processing strategy for organic solar cells (OSC) that exploits the propensity of the fullerene derivative PC₆₀BM to photo-oligomerize, which is capable of both stabilizing the polymer:PC₆₀BM active layer morphology and enhancing the device stability under thermal annealing. The observations hold for blends of PC₆₀BM with an array of benchmark donor polymer systems, including P3HT, DPP-TT-T, PTB7, and PCDTBT. The morphology and kinetics of the thermally induced PC₆₀BM crystallization within the blend films are investigated as a function of substrate and temperature. PC₆₀BM nucleation rates on SiOx substrates exhibit a pronounced peak profile with temperature, whose maximum is polymer and blend-composition dependent. Modest illumination (<10 mW/cm²) significantly suppresses nucleation, which is quantified as function of dose, but does not affect crystalline shape or growth, in the micrometer range. On PEDOT:PSS substrates, thermally induced PC₆₀BM aggregation is observed on smaller (≈100 nm) length scales, depending upon donor polymer, and also suppressed by light exposure. The concurrent thermal dissociation process of PC₆₀BM oligomers in blend films is also investigated and the activation energy of the fullerene–fullerene bond is estimated to be 0.96 ± 0.04 eV. Following light processing, the thermal stability, and thus lifetime, of PCDTBT:PC₆₀BM devices increases for annealing times up to 150 h. In contrast, PCDTBT:PC₇₀BM OSCs are found to be largely light insensitive. The results are rationalized in terms of the suppression of PC₆₀BM micro- and nanoscopic crystallization processes upon thermal annealing caused by photoinduced PC₆₀BM oligomerization

Isostructural, Deeper Highest Occupied Molecular Orbital Analogues of Poly(3-hexylthiophene) for High-Open Circuit Voltage Organic Solar Cells

We present the synthesis and characterization of two novel thiazole-containing conjugated polymers (<b>PTTTz</b> and <b>PTTz</b>) that are isostructural to poly­(3-hexylthiophene) (P3HT). The novel materials demonstrate optical and morphological properties almost identical to those of P3HT but with HOMO and LUMO levels that are up to 0.45 eV deeper. An intramolecular planarizing nitrogen–sulfur nonbonding interaction is observed, and its magnitude and origin are discussed. Both materials demonstrate significantly greater open circuit voltages than P3HT in bulk heterojunction solar cells. <b>PTTTz</b> is shown to be an extremely versatile donor polymer that can be used with a wide variety of fullerene acceptors with device efficiencies of up to 4.5%. It is anticipated that this material could be used as a high-open circuit voltage alternative to P3HT in organic solar cells