Tuning the performance of aqueous photovoltaic elastomer gels by solvent polarity and nanostructure development

Abstract

In this study, a sulfonated pentablock ionomer is considered for use as an aqueous gel electrolyte in photovoltaic elastomer gels (PVEGs) containing photosensitive dyes. Depending on the casting solvent employed, these materials order into different nanoscale morphologies, some of which inherently consist of a continuous pathway through which ions and other polar species are able to diffuse, while others transform into continuous channels upon exposure to water. Here, we examine the effect of solvent polarity during film casting, vapor annealing, and liquid immersion on block ionomer morphology and PVEG photovoltaic performance. Casting the block ionomers from a mixed nonpolar/polar solvent promotes the formation of dispersed ion-rich spherical microdomains. Alternatively, the use of a single polar solvent produces coexisting nonpolar cylinders and lamellae. Exposure of either morphology to polar solvent vapor causes the block ionomers to restructure into a lamellar morphology, whereas exposure of dispersed ion-rich microdomains to water induces a transformation to an irregular morphology composed of continuous ionic channels, which provide an effective pathway for ion diffusion and, consequently, the highest photovoltaic efficiency. In addition to their photovoltaic efficacy, these aqueous gels possess improved mechanical properties (in terms of tensile strength and elastic modulus) in the presence of photosensitive dyes. V C 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 85-95

Quasi‐Solid‐State Dye‐Sensitized Solar Cells Containing a Charged Thermoplastic Elastomeric Gel Electrolyte and Hydrophilic/phobic Photosensitizers

“…Unlike conventional TPEs that are completely nonpolar and typically exhibit moderate to strong thermodynamic interblock incompatibility (which drives self‐assembly), the SBI homologs introduced here are amphiphilic and significantly more incompatible due to the presence of ionic species along the charged block. We have previously established that these materials, without the integration of a TiO 2 layer, yield dye‐sensitized PVEGs that outperform other hydrogel‐like photovoltaics and retain robust mechanical properties even when hydrated. In this study, we introduce these SBIs into the fabrication of QS‐DSSCs.…”

“…In our previous studies, we have introduced a new thermoplastic elastomeric BCP archetype for use in photovoltaic devices. Even without the presence of a TiO 2 layer, sulfonated block ionomers (SBIs), multiblock copolymers possessing a charged midblock (illustrated in Scheme ), can be loaded with oppositely‐charged, hydrophilic photosensitive dyes to yield nanostructured photovoltaic elastomer gels (PVEGs) that possess excellent mechanical properties even when hydrated . Their photon conversion efficiency is higher than that of similar hydrogel‐based photovoltaic devices .…”

“…Even without the presence of a TiO 2 layer, sulfonated block ionomers (SBIs), multiblock copolymers [46,47] possessing a charged midblock (illustrated in Scheme 1), can be loaded with oppositely-charged, hydrophilic photosensitive dyes to yield nanostructured photovoltaic elastomer gels (PVEGs) that possess excellent mechanical properties even when hydrated. [48,49] Their photon conversion efficiency is higher than that of similar hydrogel-based photovoltaic devices. [50][51][52] The morphologies of these materials and, in turn, their photovoltaic performance can be independently controlled by solvent casting [53] and solvent vapor annealing, [54] as well as hydrothermal treatment (which can yield a disordered ioncontinuous morphology).…”

Solvent‐Templated Block Ionomers for Base‐ and Acid‐Gas Separations: Effect of Humidity on Ammonia and Carbon Dioxide Permeation

“…Recent efforts have introduced charged TPEs wherein a midblock is partially sulfonated. Technological interest in such sulfonated block ionomers (SBIs) ranges from fuel cells and proton‐exchange membranes to water‐desalination membranes, electroactive media, and organic photovoltaics, as well as molecular transport . While morphological development in nonionic block copolymers is well understood and largely controllable, a longstanding challenge of charged block copolymers in general has been kinetic entrapment due to the presence of ionic clusters that serve as additional physical crosslinks and thwart morphological equilibration .…”

Incorporation of Metallic Species into Midblock‐Sulfonated Block Ionomers

“…Ion exchange of various electrolytes using the same methodology, however, provides an attractive route by which to incorporate metal species into SBI52 and its homologs possessing a lower DOS. Ruthenium‐based electrolytes that behave as photosensitizers enable these block ionomers to function as both hydrogel and dye‐sensitized organic photovoltaics exhibiting attractive performance metrics, whereas addition of lithium ions can make block ionomers electroresponsive as ionic polymer–metal composites . Strategic incorporation of inorganic salts can likewise alter the mechanical properties of these materials .…”