Abstract
The fabrication, thickness, and structure of aerogel films composed of covalently cross-linked cellulose nanocrystals (CNCs) and poly(oligoethylene glycol methacrylate) (POEGMA) were optimized for use as electrolyte absorbers in dye-sensitized solar cells (DSSCs). The aerogel films were cast directly on transparent conducting counter electrode substrates (glass and flexible poly(ethylene terephthalate) plastic) and then used to absorb drop-cast liquid electrolyte, thus providing an alternative method of filling electrolyte in DSSCs. This approach eliminates the use of electrolyte-filling holes, which are a typical pathway of electrolyte leakage, and furthermore enables a homogeneous distribution of electrolyte components within the photoelectrode. Unlike typical in situ electrolyte gelation approaches, the phase inversion method used here results in a highly porous (>99%) electrolyte scaffold with excellent ionic conductivity and interfacial properties. DSSCs prepared with CNC–POEGMA aerogels reached similar power conversion efficiencies as compared to liquid electrolyte devices, indicating that the aerogel does not interfere with the operation of the device. These aerogels retain their structural integrity upon bending, which is critical for their application in flexible devices. Furthermore, the aerogels demonstrate impressive chemical and mechanical stability in typical electrolyte solvents because of their stable covalent cross-linking. Overall, this work demonstrates that the DSSC fabrication process can be simplified and made more easily upscalable by taking advantage of CNCs, being an abundant and sustainable bio-based material.
Highlights
Photovoltaics is the world fastest growing energy technology.The aim is that of meeting the growing energy demand and reducing the emission of greenhouse gases from fossil fuels.The European Joint Research Centre estimates that solar energy could supply 20% of the world energy consumption by 2050 and over 50% by 2100.1 Dating back to the development of the first crystalline silicon solar cell in 1954 from BellLaboratories, the widespread use of photovoltaics has been limited due to high manufacturing and environmental costs.[2,3]A newer development of photovoltaic technology is the dyesensitized solar cell (DSSC)
In the research presented here, we investigated how the thickness of covalently cross-linked aldehyde-functionalized cellulose nanocrystal and hydrazide-functionalized poly(oligoethylene glycol methacrylate) aerogels impacts DSSC performance
The dry and wetted aerogels retained their shape upon bending as shown in Figure 5 and are promising candidate materials for roll-to-roll fabrication, where devices are subjected to significant bending strain
Summary
Photovoltaics is the world fastest growing energy technology. The aim is that of meeting the growing energy demand and reducing the emission of greenhouse gases from fossil fuels. Even though the aerogel compression does increase its density, the effects are too small to cause significant impedance to diffusion This is unique compared to most gel polymer electrolytes reported in the literature where the ionic conductivity and interfacial properties are affected, and inorganic nanoparticles are sometimes added to the polymer matrix to restore DSSC efficiency.[27,45,46] As compared to the earlier work of Miettunen et al.,[30] the aerogel fabrication method here allows easier tuning of the aerogel density, porosity, degree of cross-linking (and the viscosity of the initial gel and its processability), and thickness control.
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