Printed single-walled carbon-nanotubes-based counter electrodes for dye-sensitized solar cells with copper-based redox mediators

Abstract

Here we report printed single-walled carbon nanotubes (SWCNT) as a promising catalyst material for copper redox shuttles based electrolyte in dye-sensitized solar cells (DSSC). The SWCNT layers, which were printed at low temperature could serve as an alternative catalyst material since they outperformed the traditional thermally platinized CEs by exhibiting very low charge transfer resistance (∼2.1-2.9 Ω cm 2 ) in both complete DSSCs as well as in a symmetrical CE-CE cells. The superior catalytic activity of printed SWCNT-CEs contributed to better photovoltaic performance and resulted in a higher solar-to-electrical conversion efficiency (7.0%±0.4%) than traditional Pt-CE based DSSCs (6.2% ±0.4%) in full sunlight conditions. The devices fabricated with printed SWCNTs catalyst counter electrodes also exhibited impressive open circuit voltage that almost approached 1 Volt. The champion DSSC with SWCNT CE gave a 7.5% conversion efficiency under full sun illumination and 8.3% under half sun illumination. These two efficiency values are the highest ever-reported efficiencies for SWCNT-based CEs combined with a Cu-based electrolyte in DSSCs. These results could provide a pathway for efficient DSSC-based devices, which can be integrated in futuristic consumer applications for efficiently working under both full sun light and low light intensities.

Advanced research trends in dye-sensitized solar cells

“… 25 Hence, the thickness of the thermoplastic and spacer directly influences the photovoltaic performance of DSSCs through mass transport and the diffusion resistance ( R D ) of the bulk electrolyte. 25,26,28 Presently, minimizing R D has only been realized either by adjusting the thermoplastic, adjusting the porous insulator thicknesses, 28,29 or by using low viscosity solvent-based electrolytes to produce high efficiency DSSCs. 23,30 …”

“…For the first generation of DSSCs, typically 10–20 μm thick layers of TiO 2 have been used with traditional ruthenium-based sensitizers to achieve high short circuit current densities ( J SC ). 72 With TiO 2 layers of such thickness, advanced redox couple-based electrolytes exhibit high diffusion resistance ( R D ) 28,30,73 and limit the possibility of achieving higher J SC than achieved with iodide/triiodide redox-based electrolytes. 72 …”

“…Such thinner and advanced TiO 2 PEs have also been reported to produce DSSCs with alternative Cu redox shuttle-based electrolytes, 28,51 where impressive solar-to-electrical conversion efficiencies under various light intensities are recently reported when tested with advanced light harvesters. 5,15,51,77 Table 2 highlights some of the top DSSCs produced with these advanced TiO 2 PEs combined with various sensitizers, as well as Co and Cu redox shuttle-based alternative electrolytes.…”

“…Unlike Pt, which does not have sufficient catalytic activity for use with the Co- and Cu-based redox couples, 28,59,85,86 electro-deposited PEDOT has shown good catalytic performance. Indeed, high efficiencies have been reached both at high and low light intensities with these new redox couples.…”

“…Keeping such limitations in mind, Hashmi et al recently demonstrated printable single-walled carbon nanotube (SWCNT)-based CEs as a more practical approach 28 to addressing the challenge regarding scalable production of DSSC with advanced sets of materials. Similar to graphene nanoplatelets, these printed SWCNT-based CEs also outperformed the traditional Pt nano catalyst by revealing significantly lower R CT (2–2.9 Ω cm 2 ) when loaded with Cu redox shuttle-based electrolytes.…”