Water-Based Thixotropic Polymer Gel Electrolyte for Dye-Sensitized Solar Cells

For the practical application of dye-sensitized solar cells (DSSCs), it is important to replace the conventional organic solvents based electrolyte with environmentally friendly and stable ones, due to the toxicity and leakage problems. Here we report a noble water-based thixotropic polymer gel electrolyte containing xanthan gum, which satisfies both the environmentally friendliness and stability against leakage and water intrusion. For application in DSSCs, it was possible to infiltrate the prepared electrolyte into the mesoporous TiO₂ electrode at the fluidic state, resulting in sufficient penetration. As a result, this electrolyte exhibited similar conversion efficiency (4.78% at 100 mW cm^–2) and an enhanced long-term stability compared to a water-based liquid electrolyte. The effects of water on the photovoltaic properties were examined elaborately from the cyclic voltammetry curves and impedance spectra. Despite the positive shift in the conduction band potential of the TiO₂ electrode, the open-circuit voltage was enhanced by addition of water in the electrolyte due to the greater positive shift in the I^–/I₃^– redox potential. However, due to the dye desorption and decreased diffusion coefficient caused by the water content, the short-circuit photocurrent density was reduced. These results will provide great insight into the development of efficient and stable water-based electrolytes

Highly Efficient Bifacial Dye-Sensitized Solar Cells Employing Polymeric Counter Electrodes

Dye-sensitized solar cells (DSCs) are promising solar energy conversion devices with aesthetically favorable properties such as being colorful and having transparent features. They are also well-known for high and reliable performance even under ambient lighting, and these advantages distinguish DSCs for applications in window-type building-integrated photovoltaics (BIPVs) that utilize photons from both lamplight and sunlight. Therefore, investigations on bifacial DSCs have been done intensively, but further enhancement in performance under back-illumination is essential for practical window-BIPV applications. In this research, highly efficient bifacial DSCs were prepared by a combination of electropolymerized poly­(3,4-ethylenedioxythiphene) (PEDOT) counter electrodes (CEs) and cobalt bipyridine redox ([Co­(bpy)₃]^3+/2+) electrolyte, both of which manifested superior transparency when compared with conventional Pt and iodide counterparts, respectively. Keen electrochemical analyses of PEDOT films verified that superior electrical properties were achievable when the thickness of the film was reduced, while their high electrocatalytic activities were unchanged. The combination of the PEDOT thin film and [Co­(bpy)₃]^3+/2+ electrolyte led to an unprecedented power conversion efficiency among bifacial DSCs under back-illumination, which was also over 85% of that obtained under front-illumination. Furthermore, the advantage of the electropolymerization process, which does not require an elevation of temperature, was demonstrated by flexible bifacial DSC applications