Molecular Engineering for Enhanced Charge Transfer in Thin-Film Photoanode

Abstract

We developed three types of dithieno[3,2-b;2',3'-d]thiophene (DTT)-based organic sensitizers for high-performance thin photoactive TiO films and investigated the simple but powerful molecular engineering of different types of bonding between the triarylamine electron donor and the conjugated DTT π-bridge by the introduction of single, double, and triple bonds. As a result, with only 1.3 μm transparent and 2.5-μm TiO scattering layers, the triple-bond sensitizer (T-DAHTDTT) shows the highest power conversion efficiency (η = 8.4%; V = 0.73 V, J = 15.4 mA·cm, and FF = 0.75) in an iodine electrolyte system under one solar illumination (AM 1.5, 1000 W·m), followed by the single-bond sensitizer (S-DAHTDTT) (η = 7.6%) and the double-bond sensitizer (D-DAHTDTT) (η = 6.4%). We suggest that the superior performance of T-DAHTDTT comes from enhanced intramolecular charge transfer (ICT) induced by the triple bond. Consequently, T-DAHTDTT exhibits the most active photoelectron injection and charge transport on a TiO film during operation, which leads to the highest photocurrent density among the systems studied. We analyzed these correlations mainly in terms of charge injection efficiency, level of photocharge storage, and charge-transport kinetics. This study suggests that the molecular engineering of a triple bond between the electron donor and the π-bridge of a sensitizer increases the performance of dye-sensitized solar cell (DSC) with a thin photoactive film by enhancing not only J through improved ICT but also V through the evenly distributed sensitizer surface coverage.

Fine-Tuning by Triple Bond of Carbazole Derivative Dyes to Obtain High Efficiency for Dye-Sensitized Solar Cells with Copper Electrolyte

“…Therefore, the best photovoltaic performance resulted when the triple bond was between the π-bridge and the anchor group. Notably, AJ206 exhibited a higher power conversion efficiency that approached a previous report of 11.2% with the same copper electrolyte in Figure B and other dyes containing acetylene groups based on traditional electrolytes as depicted in Figure S7 and Table S3. ,,− The DSCs were all fabricated with an effective TiO 2 area of 0.16 cm 2 and under the same fabrication conditions. By analyzing and comparing these photovoltaic parameters, we can conclude that the J sc of the device that contained AJ206 was much higher because it had a higher driving force to inject electrons into the TiO 2 conduction and the highest molar extinction coefficient of the dyes.…”

Molecular Design Strategy toward Robust Organic Dyes in Thin-Film Photoanodes

“…Dye-sensitized solar cells (DSCs) have attractive advantages such as transparency, color tunability, flexibility of devices, and excellent efficiency at low illumination. − Therefore, DSCs have immense potential not only for building integrated photovoltaics and automotive-integrated photovoltaics but also as indoor power-generating devices. In this regard, research on DSCs needs to focus on the resistance to photo-, thermal and water stresses to enhance the lifetime of DSCs and on its applications to thin-film photoanodes to enhance the transparency and flexibility of devices. − …”

Enhancement in Dye‐Sensitized Solar Cells Using Surface Plasmon Resonance Effects from Colloidal Core‐Shell Au@SiO2 Nanoparticles

“…Several strategies to increase efficiency of DSSCs have been reported in the literature. Some examples include an increase in semiconductor film thickness, changes in the size and morphology of nano‐sized or micro‐sized semiconductor material, and structural changes in dye molecules for better spectral response . An increase in semiconductor film thickness allows for higher quantity of dye loadings; however, it will result in an increased diffusion path length for photo‐generated electrons.…”