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. 2016 Jan 7:6:18756.
doi: 10.1038/srep18756.

Metal-free organic dyes for TiO2 and ZnO dye-sensitized solar cells

Gurpreet Singh Selopal  1   2 , Hui-Ping Wu  3 , Jianfeng Lu  4 , Yu-Cheng Chang  3 , Mingkui Wang  4 , Alberto Vomiero  2   5 , Isabella Concina  1   2 , Eric Wei-Guang Diau  3
Affiliations

Metal-free organic dyes for TiO2 and ZnO dye-sensitized solar cells

Gurpreet Singh Selopal et al. Sci Rep. .

Abstract

We report the synthesis and characterization of new metal-free organic dyes (namely B18, BTD-R, and CPTD-R) which designed with D-π-A concept to extending the light absorption region by strong conjugation group of π-linker part and applied as light harvester in dye sensitized solar cells (DSSCs). We compared the photovoltaic performance of these dyes in two different photoanodes: a standard TiO2 mesoporous photoanode and a ZnO photoanode composed of hierarchically assembled nanostructures. The results demonstrated that B18 dye has better photovoltaic properties compared to other two dyes (BTD-R and CPTD-R) and each dye has higher current density (Jsc) when applied to hierarchical ZnO nanocrystallites than the standard TiO2 mesoporous film. Transient photocurrent and photovoltage decay measurements (TCD/TVD) were applied to systematically study the charge transport and recombination kinetics in these devices, showing the electron life time (τR) of B18 dye in ZnO and TiO2 based DSSCs is higher than CPTD-R and BTD-R based DSSCs, which is consistent with the photovoltaic performances. The conversion efficiency in ZnO based DSSCs can be further boosted by 35%, when a compact ZnO blocking layer (BL) is applied to inhibit electron back reaction.

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Figures

Figure 1
Figure 1. Molecular structures of the B18, CPTD-R and BTD-R organic dyes.
Figure 2
Figure 2
Characterization of dye molecules: (a) absorption and (b) emission spectra of B18, CPTD-R and BTD-R in CHCl3 solution. (c) Cyclic voltammograms of B18, CPTD-R and BTD-R, obtained in in freshly distilled CHCl3 using 0.5 M Tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte in a three–electrode configuration. (d) Schematic of potential levels of B18, CPTD-R and BTD-R with HOMO and LUMO levels showing electron injection to CB of ZnO and dye regeneration by I−/I3− electrolyte.
Figure 3
Figure 3. Photovoltaic properties of standard mesoporous TiO2 DSSCs sensitized with the three different metal free organic dyes.
(a) Current density vs photovoltage curves under 1 sun illumination (AM 1.5 G, 100 mW cm−2); (b) IPCE spectra.
Figure 4
Figure 4
Comparison of electron-transport kinetics for three different dyes sensitized standard mesoporous TiO2: (a) τR vs Ne; (b) Voc vs Ne (τR: electron lifetime, Voc: open-circuit voltage and Ne: charge density).
Figure 5
Figure 5. Photovoltaic properties.
(a) Current density vs photovoltage curves under 1 sun illumination (AM 1.5 G, 100 mW cm−2); (b) IPCE spectra of three different metal free organic dyes sensitized hierarchical structured ZnO DSSCs.
Figure 6
Figure 6
Comparison of electron-transport kinetics for three different dyes sensitized hierarchical ZnO: (a) τR vs Ne; (b) Voc vs Ne; (τR: electron lifetime, Voc: open-circuit voltage, Ne: charge density).
Figure 7
Figure 7
Comparison of electron-transport kinetics for hierarchical structured ZnO and standard mesoporous TiO2 sensitized by B18, CPTD-R and BTD-R based DSSCs: (a) τR vs Ne; (b) τC vs Jsc and (c) Voc vs Ne.
Figure 8
Figure 8
(a) Current density vs photovoltage under 1 sun illumination (AM 1.5 G, 100 mW cm−2); (b) IPCE spectra for hierarchical structured ZnO DSSCs with and without BL sensitized by B18.
Figure 9
Figure 9
Comparison of electron-transport kinetics for hierarchical structured ZnO DSSCs with and without BL sensitized by B18: (a) τR vs Voc; (b) τC vs Jsc (c) τR vs Ne and (d) Voc vs Ne.
Figure 10
Figure 10. Synthesis of B18, CPTD-R and BTD-R dye molecules.
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