Solution-Processable High-Quality Graphene for Organic Solar Cells

The unique optical and electronic properties of graphene open up new opportunities for optoelectronics. This work reports the use of <i>solution-processed</i> high-quality graphene as transparent conductive electrode in an organic solar cell using an electrochemical approach. The fabricated thieno­[3,4-<i>b</i>]­thiophene/benzo­dithiophene:phenyl-C₇₁-butyric acid methyl ester (PTB7:PCB₇₁M) bulk heterojunction organic solar cell based on the exfoliated graphene (EG) anode exhibits a power conversion efficiency of 4.23%, making EG promising for next-generation flexible optoelectronic devices

Quantifying the Kinetics of the Gilch Polymerization toward Alkoxy-Substituted Poly(<i>p</i>‑phenylene vinylene)

The Gilch polymerization is one of the most popular routes toward high molecular weight alkoxy-substituted poly­(<i>p</i>-phenylene­vinylenes) (PPV) applied in, for instance, organic electronics and bioimaging. As the interplay between optoelectronic performance and (synthesis-related) defects represents an active area of research, control over the polymerization is of utmost importance. In this work we quantify for the first time the rate constants of the reaction steps of the Gilch polymerization. We obtain these values by fitting concentration transients of various key intermediates, measured by <i>in situ</i> low-temperature (−68 °C) ¹H NMR spectroscopy, to kinetic models based on sets of coupled rate equations. The modeling not only accounts for the usual processes of initiation, propagation, transfer, and radical recombination but also involves the side reaction cascade associated with the presence of residual water in the reaction mixture. The results demonstrate that chain growth initiation by active monomer dimerization is slow and rate determining. We show that a low temperature suppresses the occurrence of bisbenzyl and bisbromobenzyl coupling defects. The initiation rate is reduced by orders of magnitude compared to the propagation rate. Hence, fast chain growth occurs at a relative low concentration of radical intermediates, which suppresses defect formation due to both active monomer dimerization and radical–radical recombination

Up-Scaling Graphene Electronics by Reproducible Metal–Graphene Contacts

Chemical vapor deposition (CVD) of graphene on top of metallic foils is a technologically viable method of graphene production. Fabrication of microelectronic devices with CVD grown graphene is commonly done by using photolithography and deposition of metal contacts on top of the transferred graphene layer. This processing is potentially invasive for graphene, yields large spread in device parameters, and can inhibit up-scaling. Here we demonstrate an alternative process technology in which both lithography and contact deposition on top of graphene are prevented. First a prepatterned substrate is fabricated that contains all the device layouts, electrodes and interconnects. Then CVD graphene is transferred on top. Processing parameters are adjusted to yield a graphene layer that adopts the topography of the prepatterned substrate. The metal–graphene contact shows low contact resistances below 1 kΩ μm for CVD graphene devices. The conformal transfer technique is scaled-up to 150 mm wafers with statistically similar devices and with a device yield close to unity