Difunctionalized dyes for DSSCs based on two different scaffolds: p-tert-butylcalix[4]arene or isophthalic acid

doi:10.1016/j.dyepig.2020.108530

Dyes and Pigments

Volume 182, November 2020, 108530

https://doi.org/10.1016/j.dyepig.2020.108530 Get rights and content

Highlights

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p-tert-butylcalix [4]arene leads to a broad absorption as well as a high absorption.
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These difunctionalized dyes deliver higher efficiency than single D-π-A analogues.
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These dyes are stable up to 1000 h after the device assembly.

Abstract

Novel DSSCs (Dye Sensitized Solar Cells) have been developed with difunctionalized dyes, which are based on isophthalic acid or 4-tert-butylcalix[4]arene as scaffold and N,N-dialkylaniline as electrondonor connected to thiophene as π-spacer. This heteroaromatic ring has been used because of its thermal stability and adequate charge transfer. The use of 4-tert-butylcalix[4]arene has given rise a considerable increase of the molar extinction coefficient in this difunctionalized dye relative to the individual one, which makes them susceptible to be used in low luminosity condition. All dyes have been completely characterized. The photoelectrochemical properties of the devices prepared with or without co-adsorbate (chenodeoxycholic acid) have been determined. When co-adsorbate is added, solar cells prepared with isophthalic acid and 4-tert-butylcalix[4]arene have power conversion efficiencies of 6.0 and 6.3%, respectively; such devices also display good long-term stability up to 1000 h.

Introduction

Solar energy is a renewable alternative to face world energy demand [1]. Nowadays this market is dominated by photovoltaic energy from silicon panels. However, DSSCs are an interesting option at both academic and industrial world because of the versatility of the synthesis of dyes and the low cost in cell fabrication compared to cells prepared with silicon based devices. Most common dyes are those prepared with ruthenium [2] and porphyrins [3], which have not simple synthesis. In addition, devices prepared with ruthenium sensitizers are not environmentally friendly, and this metal is expensive and not abundant. In this context, metal-free sensitizers, with a general structure based on a donor part, a π-spacer and an acceptor (D-π-A) are an alternative. N, N-dialkylanilines have been used as donors (D) because of their simple synthesis, light absorption capacity and donor ability and also its charge transfer band appears bathochromically shifted with respect to the triphenylamine derivatives (TPA), commonly used in this field [[4], [5], [6]]. Thiophene, used as π-spacer, is a heteroaromatic ring which combines good charge transfer properties with high thermal stability [7]. The anchor group must allow the transfer of electrons from the dye to the semiconductor. The cyanoacetic acid is commonly used due to its double character as an acceptor and anchor group due to the cyano group which acts as an acceptor (A) and the carboxylic group which causes the linkage to TiO₂ surface [8].

The control of the aggregation is an important issue because it affects the performance of the DSSC device. The aggregation can be modified by changing the molecular structure of the dye, for example, reducing its molecular planarity [9], including a bulky group [10], or changing the nature [11], and the position [12] of the anchoring group. In addition, the conditions of dye-sensitization can be tuned by adding a co-adsorbent such as CDCA or modifying the time adsorption of the dye on the electrode [13].

It has been described that double D-A branched dyes with the chromophores connected via non-conjugated alkyl linkages have more intense absorbance (per chromophore unit) as compared to the single one. The use of double branched organic dyes gives rise to an improvement of photovoltaic properties; in particular an increase of the short circuit photocurrent value has been reported [14,15]. It is expected that the linkage might influence the geometrical configuration of dyes on the TiO₂ films affecting the aggregation and the performance of the device [16]. Double dyes with the alkyl linkage in either the π-bridge part [17] or the donor part were studied by Cao [18] and these studies points out that the alkyl linkage position has an effect on dye adsorption amount, dye aggregation and light harvesting ability. In this field, our research group prepared double systems based on Calix[4]arene scaffold with an alkyl linkage in the π –bridge [19,20]. As far as we know there are no dyes based on calix[4]arene derivatives with an alkyl linkage in the donor part.

Then in this work we will study the photophysical and photovoltaic properties of dyes based on calix[4]arene derivatives linked by the aniline moiety which acts as donor part (D), a thiophene as π-spacer (π) and cyanoacetic as acceptor (A). The isophthalic acid will be also studied as a rigid scaffold and it will be compared with the flexible calix[4]arene one. The effect of adsorption amount, dye aggregation and light harvesting ability will be studied and CDCA co-adsorbent will be added to avoid aggregation effect. This further understanding of the molecular characteristics of these dyes will contribute to the design of novel organic sensitizers.

Section snippets

Synthesis

Chart 1 shows the molecular structure of compounds AT-L, Cx-2-AT-L and Ft-2-AT-L. Hence, AT-L is used in this paper to compare its photovoltaic properties with those dibranched difunctionalized derivatives Cx-2-AT-L and Ft-2-AT-L. All the dyes were characterized by ¹H/¹³C NMR spectroscopy, FTIR and mass spectrometry.

Scheme 1 shows the synthesis of the compound AT-L which was obtained by a Knoevenagel condensation in chloroform between the formyl group of compound 1 [21] and cyanoacetic acid

Conclusions

Among the studied dyes, the one based on calix[4]arene scaffold has the best light harvesting ability, which gives rise to devices with good photovoltaic properties. This scaffold forms a blocking layer between TiO₂ and electrolyte leading a better suppression of the back electron transfer of the injected electrons. Consequently, dyes prepared with this scaffold show the highest V_oc values.

The addition of co-adsorbent (CDCA) plays a fundamental role for improving the photovoltaic performance,

(Dimethylamino)thiophene-2-carbaldehyde AT-L

To a solution of cyanoacetic acid (72 mg, 0.22 mmol) and piperidine (275 μL, 2.69 mmol) in dry chloroform (15 mL) a solution of the aldehyde 1 (85.1 mg, 0.33 mmol) was added. The mixture was heated to 70 °C of temperature for 48h under argon atmosphere and prevented from light; then it was cooled down to room temperature. The mixture was acidified with HCl 0.1 M (20 ml) and extracted with CH₂Cl₂ (2 x 50 mL). The organic layer was washed with water (3 x 50 mL), dried over magnesium sulfate and

CRediT authorship contribution statement

Isolda Duerto: Data curation, Visualization, Writing - original draft. Daniel Barrios: Data curation, Visualization. Javier Garín: Conceptualization. Jesús Orduna: Funding acquisition, Software, Investigation, Writing - review & editing. Belén Villacampa: Methodology, Formal analysis, Supervision, Validation, Writing - review & editing. María-Jesús Blesa: Conceptualization, Methodology, Formal analysis, Supervision, Validation, Writing - original draft, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interestsor personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We gratefully acknowledge the financial support from the Universidad de Zaragoza (UZ2019-CIE-01), the Spanish Ministry of Science and Innovation-MICINN-FEDER (Project CTQ2014–52331-R) and Gobierno de Aragón. Spain-Fondo Social Europeo (E14-17R, LMP11_18 and E47-20R). ID and DB acknowledge for the financial support of Gobierno de Aragón, Spain fellowship and PhD studentship Santander-2018 programs, respectively. Moreover, anonymous referees are gratefully acknowledged for helpful suggestions.

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View full text

Difunctionalized dyes for DSSCs based on two different scaffolds: p-tert-butylcalix[4]arene or isophthalic acid

Highlights

Abstract

Introduction

Section snippets

Synthesis

Conclusions

(Dimethylamino)thiophene-2-carbaldehyde AT-L

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgements

J Photochem Photobiol, A C

Dyes Pigments

Dyes Pigments

Dyes Pigments

Dyes Pigments

Dyes Pigments

Dyes Pigments

Nano Energy

Chem Phys

Electrochim Acta

Perovskites on trial

Nature

Contributions to the development of ruthenium-based sensitizers for dye-sensitized solar cells

Coord Chem Rev

Rational design criteria for D–π–A structured organic and porphyrin sensitizers for highly efficient dye-sensitized solar cells

J Mater Chem

Arylamine organic dyes for dye-sensitized solar cells

Chem Soc Rev

Sensitizers with rigidified-aromatics as the conjugated spacers for dye-sensitized solar cells

J Mater Chem

Multi-anchored sensitizers for dye-sensitized solar cells

Sustain Energy Fuels

Aggregation-free branch-type organic dye with a twisted molecular architecture for dye-sensitized solar cells

Energy Environ Sci