Ga In Lee

Broadband energy transfer to sensitizing dyes by mobile quantum dot mediators in solar cells

The efficiency of solar cells depends on absorption intensity of the photon collectors. Herein, mobile quantum dots (QDs) functionalized with thiol ligands in electrolyte are utilized into dye–sensitized solar cells. The QDs serve as mediators to receive and re–transmit energy to sensitized dyes, thus amplifying photon collection of sensitizing dyes in the visible range and enabling up–conversion of low-energy photons to higher-energy photons for dye absorption. The cell efficiency is boosted by dispersing QDs in electrolyte, thereby obviating the need for light scattering1 or plasmonic2 structures. Furthermore, optical spectroscopy and external quantum efficiency data reveal that resonance energy transfer due to the overlap between QD emission and dye absorption spectra becomes dominant when the QD bandgap is higher than the first excitonic peak of the dye, while co–sensitization resulting in a fast reduction of oxidized dyes is pronounced in the case of lower QD band gaps.

Coupled Near‐ and Far‐Field Scattering in Silver Nanoparticles for High‐Efficiency, Stable, and Thin Plasmonic Dye‐Sensitized Solar Cells

Here, we report plasmonically enhanced thin dye-sensitized solar cells (DSSCs) in an imidazolium-dicyanamide based ionic liquid, in which size-controlled metal (silver) nanoparticles (AgNPs) with passivation layers of a few nanometers are arranged into the electrolyte and photo-electrodes. It was revealed that the AgNPs in the electrolyte and the photo-electrode have distinct effects on device performance via different coupling mechanisms. Strong far-field scattering is critical in the electrolyte while near-field scattering is efficient in the photo-electrode. Indeed, we find that the power conversion efficiency of the DSSC can be substantially improved by a synergistic arrangement of the AgNPs in the electrolyte and the photo-electrode. Furthermore, an imidazolium-dicyanamide based nonvolatile ionic liquid electrolyte for MNPs is demonstrated to provide thin plasmonic DSSCs with good stability.

Fermi energy level tuning for high performance dye sensitized solar cells using sp2 selective nitrogen-doped carbon nanotube channels

Here, we find that doping sp(2) selective nitrogen, N sp(2), into carbon nanotube (CNT) channels induces a positive shift in the Fermi level of TiO(2) photoelectrodes. It is found that this results in the large diffusion coefficient of solar driven electrons for increasing the photocurrent as well as in the low recombination rate for improving open circuit voltage with 0.74 V, which could not be overcome by using pristine CNT channels with 0.66 V.