Conformational engineering of co-sensitizers to retard back charge transfer for high-efficiency dye-sensitized solar cells

Abstract

We demonstrate that the post-adsorption of small molecules (a phenothiazine-based dye) on the porphyrin-sensitized TiO 2 anode surface plays dual roles: (1) to greatly retard the back reaction between conduction-band electrons in TiO 2 and the oxidized species) in the electrolyte and (2) to enhance the spectral response of solar cells. These two effects finally give rise to device efficiencies exceeding 10%, which are superior to those of individual dye-sensitized devices by either porphyrin (7.4%) or phenothiazine (8.2%) under the same conditions. Experimental analyses show that the incoming small molecules are adsorbed in the interstitial site of porphyrin dyes, forming densely surface packed molecules and thus impeding the I 3 À species from approaching the TiO 2 surface. Since a broad range of ruthenium-based dyes and porphyrin-based photosensitizers possess relatively large molecular volumes, this method is anticipated to be applicable for further improving the energy conversion efficiency of devices sensitized by these two classes of dyes.

Panchromatic light harvesting by N719 with a porphyrin molecule for high-performance dye-sensitized solar cells

“…2a), 17,21 with absorption coefficients of 1.67 Â 10 5 M À1 cm À1 and 0.47 Â 10 5 M À1 cm À1 , respectively. The absorption features of HD18 anchoring onto TiO 2 lm are similar to those in solution ( Fig.…”

Solar Cells Sensitized with Porphyrin Dyes Containing Oligo(Ethylene Glycol) Units: A High Efficiency Beyond 12 %

“…Furthermore, the broad absorption peak of PT-C6 from 350 to 560 nm [50] (Figure 2) could fill up the weak absorption regions at both sides of the Soret band of the porphyrin dyes. [31,49,52] The absorption bands of the spectra on the TiO 2 films ( Figure S2 in the Supporting Information) were broadened compared with those observed in solutions, which should indicate an enhancement of the lightharvesting ability. [53] Figure 1.…”

Role of Co‐Sensitizers in Dye‐Sensitized Solar Cells

“…(Figure 15). [61] Therefore, these data suggest that the proposed method of applying small molecules to retard recombination kinetics and enhance light harvesting is ab enefit of co-sensitized devices.…”

“…Chen and co‐workers highlighted that small dye molecules can serve as both co‐adsorbent to retard back electron transfer and light harvester when co‐sensitized with large molecules. The co‐sensitized devices (2Flu‐ZnP‐COOH+PtC6) exhibits significant improved PCE of 10.1 % ( J SC =mA cm −2 , V OC =0.73 V, and FF=0.71) compared with the devices individually sensitized by 2Flu‐ZnP‐COOH ( J SC =15.78 mA cm −2 , V OC =0.70 V, FF=0.67, and PCE=7.4 %) or phenothiazine‐based co‐sensitizer PTC6 ( J SC =14.70 mA cm −2 , V OC =0.78 V, FF=0.69, and PCE=8.2 %) owing to enhancement of charge injection and retardation of the back‐electron transfer (Figure ) . Therefore, these data suggest that the proposed method of applying small molecules to retard recombination kinetics and enhance light harvesting is a benefit of co‐sensitized devices.…”

“…The spatial arrangement of the two types of dye molecules adsorbed on TiO 2 nanoparticlesurface.R eproducedf rom Ref [61]. with permission from the Royal Society of Chemistry.…”