Molecular Engineering of D–D−π–A-Based Organic Sensitizers for Enhanced Dye-Sensitized Solar Cell Performance

A series of molecularly engineered and novel dyes WS1, WS2, WS3, and WS4, based on the D35 donor, 1-(4-hexylphenyl)-2,5-di­(thiophen-2-yl)-1<i>H</i>-pyrrole and 4-(4-hexylphenyl)-4<i>H</i>-dithieno­[3,2-<i>b</i>:2′,3′-<i>d</i>]­pyrrole as π-conjugating linkers, were synthesized and compared to the well-known LEG4 dye. The performance of the dyes was investigated in combination with an electrolyte based on Co­(II/III) complexes as redox shuttles. The electron recombination between the redox mediators in the electrolyte and the TiO₂ interface decreases upon the introduction of 4-hexylybenzene entities on the 2,5-di­(thiophen-2-yl)-1<i>H</i>-pyrrole and 4<i>H</i>-dithieno­[3,2-<i>b</i>:2′,3′-<i>d</i>]­pyrrole linker units, probably because of steric hindrance. The open circuit photovoltage of WS1-, WS2-, WS3-, and WS4-based devices in combination with the Co­(II/III)-based electrolyte are consistently higher than those based on a I^–/I₃^– electrolyte by 105, 147, 167, and 75 mV, respectively. The WS3-based devices show the highest power conversion efficiency of 7.4% at AM 1.5 G 100 mW/cm² illumination mainly attributable to the high open-circuit voltage (<i>V</i>_OC)

Efficient Dye-Sensitized Solar Cells with Voltages Exceeding 1 V through Exploring Tris(4-alkoxyphenyl)amine Mediators in Combination with the Tris(bipyridine) Cobalt Redox System

Tandem redox electrolytes, prepared by the addition of a tris­(<i>p</i>-anisyl)­amine mediator into classic tris­(bipyridine)­cobalt-based electrolytes, demonstrate favorable electron transfer and reduced energy loss in dye-sensitized solar cells. Here, we have successfully explored three tris­(4-alkoxyphenyl)­amine mediators with bulky molecular structures and generated more effective tandem redox systems. This series of tandem redox electrolytes rendered solar cells with very high photovoltages exceeding 1 V, which approaches the theoretical voltage limit of tris­(bipyridine)­cobalt-based electrolytes. Solar cells with power conversion efficiencies of 9.7–11.0% under 1 sun illumination were manufactured. This corresponds to an efficiency improvement of up to 50% as compared to solar cells based on pure tris­(bipyridine)­cobalt-based electrolytes. The photovoltage increases with increasing steric effects of the tris­(4-alkoxyphenyl)­amine mediators, which is attributed to a retarded recombination kinetics. These results highlight the importance of structural design for optimized charge transfer at the sensitized semiconductor/electrolyte interface and provide insights for the future development of efficient dye-sensitized solar cells