MULTIFUNCTIONAL METAL-ORGANIC FRAMEWORKS FOR NEXT-GENERATION DYE SENSITIZED SOLAR CELLS

摘要

Dye-sensitized solar cells (DSSC) comprised of organic lightharvestingrnmolecules bound to mesoporous titanium dioxide havernachieved remarkably high power conversion efficiencies in recentrnyears. The high PCE results from separating light absorption,rnelectron transport, and hole transport to individual materials andrnindependently optimizing these materials. Consequently, the DSSCrnarchitecture enables individual components to be independentlyrnoptimized to a greater extent than bulk heterojunction (BHJ) designs.rnIt is also relatively free of morphology- and microstructure-drivenrneffects that plague BHJ solar cells. Nevertheless, efficiencies ≥20%rnwill likely be necessary to reach the 2020 $1/W installed cost set byrnthe U.S. DOE, driving continued research aimed at discovering newrnmaterials. Improving light harvesting by extending dye absorptionrninto the near infrared (800 – 1000 nm), increasing the open-circuitrnvoltage by reducing overpotentials associated with dye regenerationrnand charge injection, and minimizing charge recombination arernstrategies likely to have the greatest impact on improving the PCE.1rnMetal-Organic Frameworks (MOFs), which are crystallinernsupramolecular materials,offer a level of synthetic and structuralrnversatility unavailable in all other known light-harvesting materials.rnMoreover, these materials are nanoporous, creating newrnopportunities to control processes at the atomic, molecular, andrnmesoscales. This presentation will summarize our efforts to developrnboth fundamental understanding and practical synthetic approachesrnneeded to develop MOFs as a new class of DSSC materials.rnSpecifically, we are using non-empirically tuned long-rangerncorrected density functional theory (DFT) to compute electronicrnproperties (fundamental and optical gaps) of linkers with the aim ofrnextending light absorption onset to at least 900 nm. To enable thesernto be incorporated into devices, we are developing growth methodsrnfor depositing MOFs on DSSC electrodes and are focusing on thernSURMOFs class of MOF thin-film structures,4 which have tailorablern2D layered structures separated by “pillar” ligands. Atomic layerrndeposition (ALD) is being used to deposit conduction band offsetrnlayers and to enhance MOF nucleation and growth. Finally, we arernaddressing the challenges of integrating these novel materials intornDSSC devices and will discuss the fabrication of prototype devicesrnand their performance. Overall, our results represent encouragingrnprogress and suggest that expanding the realm of MOF applicationsrninto opto-electronic devices is an achievable goal.