The high cost of electricity produced by solar cells compared with electricity from other energy sources inhibits a more widespread adoption of solar energy. Here, a low-cost monolithic all-solid-state dye-sensitized solar cell (DSSC) was developed with a mesoscopic carbon counter electrode (CE). Based on the design of a triple layer structure, the TiO2 working electrode layer, ZrO2 spacer layer and carbon counter electrode (CE) layer are constructed on a single conducting glass substrate by screen-printing. With a vacuum pore-filling technique, solid-state materials such as PEO/PVDF polymer composite, poly(3-hexylthiophene) (P3HT) and 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)- 9,9’-spirobifluorene (spiro-OMeTAD) hole transport material (HTM) could effectively infiltrate the multilayer thick films to assemble all-solid-state devices. The high surface area and large pore volume favor the penetration of the solidstate electrolyte materials and could reduce the resistance of the interface between CE and solid-state electrolyte. Correspondingly, efficiency up to 3.23% was obtained with polymer composite electrolyte and the dye of N719. With the dye of D102, efficiencies of 3.11% and 3.45% were obtained for the HTMs of P3HT and spiro-OMeTAD based electrolytes. In addition, a mesoscopic methylammonium lead iodide (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>) perovskite/TiO2 heterojunction solar cell was developed based on the monolithic structure and showed an efficiency of up to 6.53%. This design for monolithic DSSC with a carbon CE presents a promising commercial application prospect for this photovoltaic technology.
In this study, a novel bifacially active transparent dye-sensitized solar cell (DSSCs) assembled with a transparent poly(3,4-ethylenedioxythiophene) (PEDOT) counter electrode and a colorless iodine-free polymer gel (IFPG) electrolyte was developed. The IFPG electrolyte was prepared by employing an ionic liquid (1,2-dimethyl-3-propylinmidazolium iodide, DMPII) as the charge transfer intermediate and a polymer composite as the gelator without the addition of iodine, exhibiting high conductivity and non-absorption characters. PEDOT electrodes were prepared via a facile electro-polymerization method. By controlling the amount of polymerization charge capacity, we optimized the PEDOT electrodes with high transparency and a favorable activity for catalyzing the IFPG electrolyte. The bifacial DSSCs device fabricated by this kind of transparent PEDOT electrode and colorless IFPG electrolyte showed a power conversion efficiency (PCE) of 6.35% and 4.98% at 100 mW cm<sup>-2</sup> AM1.5 illumination corresponding to front- and rear-side illumination. It is notable that the PCE under rear-side illumination approaches 80% that of front-side illumination. Moreover, the device shows excellent stability as confirmed by aging test. These promising results highlight the enormous potential of this transparent PEDOT CE and colorless IFPG electrolyte in scaling up and commercialization of low cost and effective bifacial DSSCs.
We have developed a monolithic quasi-solid-state dye-sensitized solar cell (DSSC) based on graphene modified mesoscopic carbon counter electrode (GC-CE), which offers a promising prospect for commercial applications. Based on the design of a triple layer structure, the TiO<sub>2</sub> working electrode layer, ZrO<sub>2</sub> spacer layer and carbon counter electrode (CE) layer are constructed on a single conducting glass substrate by screen-printing. The quasi-solid-state polymer gel electrolyte employs a polymer composite as the gelator and could effectively infiltrate into the porous layers. Fabricated with normal carbon counter electrode (NC-CE) containing graphite and carbon black, the device shows a power conversion efficiency (<i>PCE</i>) of 5.09% with the fill factor (<i>FF</i>) of 0.63 at 100 mW cm<sup>-2</sup> AM1.5 illumination. When the NC-CE is modified with graphene sheets, the <i>PCE</i> and <i>FF</i> could be enhanced to 6.27% and 0.71, respectively. This improvement indicates excellent conductivity and high electrocatalytic activity of the graphene sheets, which have been considered as a promising platinum-free electrode material for DSSCs.