PEDOT-graphene counter-electrode for solar and improved artificial light conversion in regular, bifacial and FTO-less cobalt mediated DSSCs

Dye-sensitized solar cells (DSSC) are emerging as an attractive indoor photovoltaic technology to address the challenge of sustainable powering wireless sensor nodes for Internet of Things (IoTs) and low power consuming electronics. This study reports on new highly electrochemically active PEDOT:PSS (PP) and graphene nano platelets (GNPs) composite layer with protruding morphology as counter-electrode for Co(III/II) mediated DSSCs. The PP:GNP counter-electrode layer displays an apparent activation energy (E-a) for charge transfer with Co(bpy)(3+/2+) ions of 6.2 kJ.mol(-1), almost twofold lower than pristine PP. The fraction of oxidized EDOT units in the polymer increased upon graphene nanoplatelets doping; the work function of PP:GNPs catalyst was best suited to the Co(bpy)(3+/2+) redox potential than pristine PP. Despite the significant difference in the catalytic activity, conventional DSSCs with PP and PP:GNP counter-electrodes display similar power conversion efficiency (PCE) of 11.0% and 10.7%, respectively, under 1-Sun illumination. A considerable advantage of the PP:GNP counter-electrode layer emerges under artificial light; DSSCs with PP:GNP cathode render PCE of 29.7% at 1000 lx, surpassing the counterparts with PP counter-electrode. Protruding from the PP matrix film, GNPs particles shorten the effective diffusion path for Cobalt ions and decrease the device resistance; higher photocurrent is possible under low power illumination. Transparency of ca. 65% in the visible region and superior electrical conductivity of the PP:GNP films allow using them in FTO-less bifacial devices; DSSCs with bare soda-lime glass substrates for the cathode displayed a PCE of 9.4% under 1-Sun and 21.9% and 18.7% under 1000 lx, for front and back illumination respectively. This makes PP:GNP counter-electrode very attractive for the cost-effective DSSCs targeting indoor light conversion.

Automated summary

Dye-sensitized solar cells (DSSC) are a promising technology for indoor photovoltaics in powering wireless sensor nodes for Internet of Things (IoTs). This study presents a new PEDOT:PSS (PP) and graphene nano platelets (GNPs) composite layer as a counter-electrode for Co(III/II) mediated DSSCs, which exhibits higher electrochemical activity and protruding morphology. Despite the difference in catalytic activity, the PP:GNP counter-electrode shows comparable power conversion efficiency (PCE) to pristine PP in traditional DSSCs, but outperforms PP under artificial light.