Highly Efficient Light Harvesting for High-Performance Polymer Solar Cells

Department of Energy EngineeringPolymer solar cells (PSCs) have gained a lot of attention due to their promising merits such as low cost, mechanical flexibility and solution processability for large area fabrication. Of various strategies, the surface plasmon resonance (SPR) effect using metal nanoparticles (MNPs), morphology control by processing additives, and ternary blend based bulkheterojunction (BHJ) are promising and efficient method to lead to maximizing the performance of PSCs. First, SPR effect from a localized electromagnetic surface wave at the metal and dielectric interface is effective way to enable active layer to absorb more incident light by field enhancement near MNPs. Second, morphology control by processing additives is one of the efficient methods to improve the PSCs accompanied with various morphology engineerings such as nanofibrilar structure, smooth surface, vertical phase separation etc.. Third, ternary blend sytem of PSCs is also promising engineering to achicve many advantages including compensated light absorption and tuning of built-in potential of BHJ. Here, I report the SPR effect using PEDOT electrode incorporated with silver nanopartices (Ag NPs) for highly efficient ITO-free PSCs and polymer light-emitting diodes (PLEDs). Ag NPs can be easily synthesized and then dissolved in PEDOT:PSS electorode. This PEDOT:PSS electrode with Ag NPs electrode contributes to increments in light absorption/emission in the active layer, respectively, by enhanced electric field distribution. I also report morphology engineering of active layer using various conjugated polymers and processing additives with thick active layer to obtain more light absorption and higher efficieny with thick active layer. PSCs based on semi-crystalline, low band gap (LBG) polymers are fabricated with single-cell architecture using diphenyl ether (DPE) as a processing additive. By using DPE additive, the semi-crystalline polymer, PPDT2FBT, form a well-distributed nano-fibrillar networked morphology with PC71BM with balanced hole and electron mobilities. Notably, PPDT2FBT:PC71BM with DPE shows high efficiency event at ~ 1μm film thickness with well-formed isotropic morphology. DTDPPTT (P2) polymer also demonstrate bicontinuous interpenetrating donor:acceptor (D:A) network in both lateral and vertical direction of thick BHJ film with DPE additive. Finally, I present efficient ternary PSCs via the incorporation of both PC61BM and PC71BM mixture as mixed acceptors and the conjugated polymer, PTBT as a donor. This ternary blend system results in a remarkable improvement in the power conversion efficieny compared to binary mixtures of the components via enhanced light absorption by PC71BM and balanced chargetransport by PC61BM. These virious and efficient methods using plasmonic MNPs, morphology engineering, and ternary blend may offer possibility for commercialization of PSCs.ope

Cellular stress-induced up-regulation of FMRP promotes cell survival by modulating PI3K-Akt phosphorylation cascades

<p>Abstract</p> <p>Background</p> <p>Fragile X syndrome (FXS), the most commonly inherited mental retardation and single gene cause of autistic spectrum disorder, occurs when the Fmr1 gene is mutated. The product of Fmr1, fragile X linked mental retardation protein (FMRP) is widely expressed in HeLa cells, however the roles of FMRP within HeLa cells were not elucidated, yet. Interacting with a diverse range of mRNAs related to cellular survival regulatory signals, understanding the functions of FMRP in cellular context would provide better insights into the role of this interesting protein in FXS. Using HeLa cells treated with etoposide as a model, we tried to determine whether FMRP could play a role in cell survival.</p> <p>Methods</p> <p>Apoptotic cell death was induced by etoposide treatment on Hela cells. After we transiently modulated FMRP expression (silencing or enhancing) by using molecular biotechnological methods such as small hairpin RNA virus-induced knock down and overexpression using transfection with FMRP expression vectors, cellular viability was measured using propidium iodide staining, TUNEL staining, and FACS analysis along with the level of activation of PI3K-Akt pathway by Western blot. Expression level of FMRP and apoptotic regulator BcL-xL was analyzed by Western blot, RT-PCR and immunocytochemistry.</p> <p>Results</p> <p>An increased FMRP expression was measured in etoposide-treated HeLa cells, which was induced by PI3K-Akt activation. Without FMRP expression, cellular defence mechanism via PI3K-Akt-Bcl-xL was weakened and resulted in an augmented cell death by etoposide. In addition, FMRP over-expression lead to the activation of PI3K-Akt signalling pathway as well as increased FMRP and BcL-xL expression, which culminates with the increased cell survival in etoposide-treated HeLa cells.</p> <p>Conclusions</p> <p>Taken together, these results suggest that FMRP expression is an essential part of cellular survival mechanisms through the modulation of PI3K, Akt, and Bcl-xL signal pathways.</p

>1000-Fold Lifetime Extension of a Nickel Electromechanical Contact Device via Graphene

Micro-/nano-electromechanical (M/NEM) switches have received significant attention as promising switching devices for a wide range of applications such as computing, radio frequency communication, and power gating devices. However, M/NEM switches still suffer from unacceptably low reliability because of irreversible degradation at the contacting interfaces, hindering adoption in practical applications and further development. Here, we evaluate and verify graphene as a contact material for reliability-enhanced M/NEM switching devices. Atomic force microscopy experiments and quantum mechanics calculations reveal that energy-efficient mechanical contact–separation characteristics are achieved when a few layers of graphene are used as a contact material on a nickel surface, reducing the energy dissipation by 96.6% relative to that of a bare nickel surface. Importantly, graphene displays almost elastic contact–separation, indicating that little atomic-scale wear, including plastic deformation, fracture, and atomic attrition, is generated. We also develop a feasible fabrication method to demonstrate a MEM switch, which has high-quality graphene as the contact material, and verify that the devices with graphene show mechanically stable and elastic-like contact properties, consistent with our nanoscale contact experiment. The graphene coating extends the switch lifetime >103 times under hot switching conditions