Boosting the Efficiency of Low-Cost T-C-O-Less Dye-Sensitized Solar Cells Employing Nanoparticle Spacers and Cobalt Complex Redox Shuttle

A strategy has been explored to enhance the diffusion of Co2+/3+ species through the dye-stained nanoparticle spacer employed as an electrolyte absorbing layer with different nanoparticle sizes of TiO2 (30 and 20 nm) and ZrO2 (15 nm) films in transparent conducting oxide-less back-contact dye-sensitized solar cells (T-C-O-less B-C-DSCs). A dye-stained nanoparticle spacer with a relatively larger particle of the TiO2 (30 nm) film brought about easy diffusion of cobalt(II/III) complexes leading to an enhanced photoconversion efficiency (PCE) of 6.55% as compared to relatively smaller nanoparticle of the TiO2 (20 nm) film (4.95%) and ZrO2 (15 nm) film (2.03%). The T-C-O-less B-C-DSC exhibits a lower PCE of 6.55% relative to the T-C-O-based DSC (9.10%) owing to relatively hampered diffusivity of [Co(bpy)3]3+/2+ complexes through perforated holes of the SS-mesh as well as the nanoparticle spacer. A differential study reveals that the cobalt electrolyte exhibits much improved light accumulation in the range 330–430 nm relative to the iodine electrolyte counterpart. The corrosion study of the SS-mesh and Ti-protected SS-mesh reveals that stable T-C-O-less B-C-DSCs can be attained only by the cobalt electrolyte because of its mild nature toward the SS-mesh and Ti metal as compared to the iodine electrolyte.