Planar D–D−π-A Organic Sensitizers for Thin-Film Photoanodes

Abstract

The planarity of an organic sensitizer is one of the most crucial factors for determining molar absorptivity and intramolecular charge transfer (ICT). The photovoltaic performance of dye-sensitized solar cells dramatically changed depending on the planarity of the donor, although all dyes exhibited similar extinction coefficients, electrochemical characteristics, as well as the amount of loaded dye. The power conversion efficiency (PCE) of planar donor dyes was 3 times greater than that of twisted donor dyes because of more rapid ICT. In addition, RK-3 dye, characterized by additional donor groups on an indoline unit, exhibited broad light-harvesting ability with higher performance as compared to those observed for planar dyes with a single donor attached to the thin-film photoanode (1.8 μm transparent + 2.5 μm scattering film). The champion cell of RK-3 exhibited a PCE of 10.3% when the thickness of the active film increased to 3.5 μm, as well as when an antireflection layer was applied with an iodine-based electrolyte.

D–A–D Based Complementary Unsymmetrical Squaraine Dyes for Co-sensitized Solar Cells: Enhanced Photocurrent Generation and Suppressed Charge Recombination Processes by Controlled Aggregation

“…Interfacial electron transfer kinetics associated with a photoexcited sensitizer and semiconducting metal oxide has been the topic of frontier research for the last three decades ever since the fruition of solar energy conversion by dye-sensitized solar cells (DSSCs). − Light absorbing sensitizer molecules play an important role in harvesting solar energy besides anode, electrolyte, and cathode materials in DSSC devices. Ease of tuning the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and the high extinction coefficient of organic sensitizers drew the attention of organic chemists to come up with different dye architectures such as D–A, D−π–A, D–A−π–A, D–D−π–A, and D–A–D to harvest visible, far-red, and NIR regions of the solar spectrum in compared to transition metal based light absorbing complexes. Aggregation of dyes on the semiconducting metal oxide surface and recombination of photoinjected electrons in the TiO 2 combined with the oxidized electrolyte are found to be detrimental factors for DSSC device performance .…”

Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells: Position of the Anchoring Group Controls the Orientation and Self-Assembly of Sensitizers on the TiO2 Surface and Modulates Its Flat Band Potential

“…Ruthenium complex based sensitizers have exhibited DSSC device performances of over 11% . Further metal-free organic sensitizers have attracted wide attention due to their ease of tuning the light-harvesting properties by the synthetic design of D−π–A, D–A−π–A, D–D′−π–A, and D–A–D , based sensitizers. High DSSC device performance has been achieved by proper molecular engineering of the sensitizers recently by considering both electronic and steric factors. , Electronic coupling between the dye components such as donor, π-spacer, acceptor, and anchoring unit is the important factor that governs light-harvesting property, photoinduced charge transfer from donor to acceptor within the sensitizer, and further photoexcited dye to the semiconducting metal oxide. , Further, planarization of the donor , and π-spacer , showed modulated electronic properties with improved device performance.…”

“…7 Ruthenium complex based sensitizers have exhibited DSSC device performances of over 11%. 8 Further metal-free organic sensitizers have attracted wide attention due to their ease of tuning the light-harvesting properties by the synthetic design of D−π−A, 9 D−A−π−A, 10 D−D′−π−A, 11 and D−A−D 12,13 based sensitizers. High DSSC device performance has been achieved by proper molecular engineering of the sensitizers recently by considering both electronic and steric factors.…”

Molecular Engineering of Indoline Dyes and Their Application in Dye-Sensitized Solar Cells: Effect of Planarity and Side Chain on Interfacial Charge-Transfer Processes

“…During the last decade, organic dyes have attracted considerable attention as powerful candidates of sensitizers in dye-sensitized solar cells (DSSCs), due to their relatively high power conversion efficiency, easy synthesis and purification, and more importantly, tunable properties. − Most properties of organic dyes, such as optical and electrochemical properties, can be easily regulated by the modification of their molecular structure, including the donor, − π-linker, − and acceptor segments. − Besides, interfacial charge-transfer processes during the operation of DSSCs can also be affected by molecular engineering of the dye to a considerable extent.…”