Panoramic View of Electrochemical Pseudocapacitor and Organic Solar Cell Research in Molecularly Engineered Energy Materials (MEEM) (original) (raw)
Related papers
2015
Organic photovoltaics are a potential source for cheap renewable energy. However oneof the main limitations to the field thus far has been scalability. Power conversionefficiencies of photovoltaic films made on the laboratory scale of a couple of mm2can be as high as 10%. However when the device area is increased to even tens of mm2power conversion efficiency plummets. This work presented in this dissertation focuseson understanding and circumventing the issues limiting the expansion of photovoltaicprocessing to larger device areas.One method of maintaining photovoltaic efficiency over a large range of device areasis to use self-assembling materials to control the active layer morphology. Thesematerials should give the preferred morphology regardless of substrate size. I first studyphotovoltaic devices utilizing self-assembling fullerenes designed to form nanometerscale wires within the film active layer. I show that fullerene that are able to form these nano-wires give a higher dev...
Main-Chain Fullerene Polymers for Photovoltaic Devices
Macromolecules, 2009
A prototype for a new class of macromolecules with a high fraction of fullerene is proposed. Their facile synthesis, modular structure, electronic activity, and novel solid-state behavior make them promising materials for photovoltaic applications. Controlled reversible-deactivation radical additions of the sterically bulky 1,4-bis(methylcyclohexyl ether)-2,5-dibromomethyl benzene to fullerene are indicated by GPC, NMR, and TGA studies to yield oligomers and polymers containing C 60 in the main chain. UV and cyclic voltammetry indicate that the C 60 undergoes mainly 1,4-additions and a minority (ca. 20%) of 1,2-additions to make a regio-irregular macromolecule. The same reaction performed in the presence of 1,4-bis(methylcyclohexyl ether)-2-bromomethyl benzene, resulting in macromolecules with bromomethyl-free chain ends, permitted confirmation of the aforementioned characteristics. The unusual reptation of the poly{(1,4-fullerene)-alt-[1,4-dimethylene-2,5bis(cyclohexylmethyl ether)phenylene]}s (PFDP) in an Al/Ca/poly(3-hexylthiophene)-blend-PFDP/PEDOT-blend-PSS/ITO/glass structured device is demonstrated by AFM to yield nanoclusters at a scale (ca. 20 nm) favorable to exciton capture. Even without optimization of the chemical structure or the device, this prototype reached promising power conversion efficiencies of 1.6%.
All-organic bulk heterojunction solar cells based on blends of conjugated polymers with fullerenes have recently surpassed the 8% efficiency mark and are well on their way to the industrially relevant ∼15% threshold. Using a low band-gap conjugated polymer, we have recently shown that polymer side chain engineering can lead to dramatic improvement in the in-plane charge carrier mobility. In this article, we investigate the effectiveness of siloxy side chain derivatization in controlling the photovoltaic performance of polymer:[6,6]-phenyl-C[71]-butyric acid methyl ester (PC 71 BM) blends and hence its influence on charge transport in the outof-plane direction relevant for organic solar cells. We find that, in neat blends, the photocurrent of the polymer with siloxy side chains (PII2T-Si) is 4 times greater than that in blends using the polymer with branched aliphatic side chains (PII2T-ref). This difference is due to a larger out-of-plane hole mobility for PII2T-Si brought about by a largely face-on crystallite orientation as well as more optimal nanoscale polymer:PC 71 BM mixing. However, upon incorporating a common processing additive, 1,8-diiodooctane (DIO), into the spin-casting blend solution and following optimization, the PII2T-ref:PC 71 BM OPV device performance undergoes a large improvement and becomes the better-performing device, almost independent of DIO concentration (>1%). We find that the precise amount of DIO plays a larger role in determining the efficiency of PII2T-Si:PC 71 BM, and even at its maximum, the device performance lags behind optimized PII2T-ref:PC 71 BM blends. Using a combination of atomic force microscopy and small-and wide-angle X-ray scattering, we are able to elucidate the morphological modifications associated with the DIO-induced changes in both the nanoscale morphology and the molecular packing in blend films.
Journal of the American Chemical Society, 2014
The performance of organic photovoltaic (OPV) material systems are hypothesized to depend strongly on the intermolecular arrangements at the donor:fullerene interfaces. A review of some of the most efficient polymers utilized in polymer:fullerene PV devices, combined with an analysis of reported polymer donor materials wherein the same conjugated backbone was used with varying alkyl substituents, supports this hypothesis. Specifically, the literature shows that higherperforming donor−acceptor type polymers generally have acceptor moieties that are sterically accessible for interactions with the fullerene derivative, whereas the corresponding donor moieties tend to have branched alkyl substituents that sterically hinder interactions with the fullerene. To further explore the idea that the most beneficial polymer:fullerene arrangement involves the fullerene docking with the acceptor moiety, a family of benzo[1,2-b:4,5-b′]dithiophene−thieno[3,4-c]pyrrole-4,6dione polymers (PBDTTPD derivatives) was synthesized and tested in a variety of PV device types with vastly different aggregation states of the polymer. In agreement with our hypothesis, the PBDTTPD derivative with a more sterically accessible acceptor moiety and a more sterically hindered donor moiety shows the highest performance in bulk-heterojunction, bilayer, and low-polymer concentration PV devices where fullerene derivatives serve as the electron-accepting materials. Furthermore, external quantum efficiency measurements of the charge-transfer state and solid-state two-dimensional (2D) 13 C{ 1 H} heteronuclear correlation (HETCOR) NMR analyses support that a specific polymer:fullerene arrangement is present for the highest performing PBDTTPD derivative, in which the fullerene is in closer proximity to the acceptor moiety of the polymer. This work demonstrates that the polymer:fullerene arrangement and resulting intermolecular interactions may be key factors in determining the performance of OPV material systems.
Meso-Structure Formation for Enhanced Organic Photovoltaic Cells
Organic Letters, 2005
Formation of a controlled fullerene mesophase within an organic host system has enabled us to create high-power conversion efficiency photovoltaics. This mesophase is formed using thermal gradients that provide a fluidic mobility of the fullerenes allowing for greater dispersion of nanocrystalline 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)C 61 (PCBM) within regioregular poly(3-hexylthiophene) (P3HT). From this reorganization of the component materials in the matrix the overall efficiency of the system jumps dramatically from the roughly 2.4% to 5.2%.
Depositing Fullerenes in Swollen Polymer Layers via Sequential Processing of Organic Solar Cells
Advanced Energy Materials, 2015
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