Linker effect in organic donor–acceptor dyes for p-type NiO dye sensitized solar cells

Abstract

Three organic donor-acceptor dyes with different bridging ligands are reported for p-type NiO dye-sensitized solar cells (DSCs). The 3,4-ethoxythiophene linker outperforms thiophene and phenyl groups giving the best solar cell performance with J sc ¼ 1.74 mA cm À2 , V oc ¼ 90 mV, FF ¼ 0.38, and an efficiency of 0.060%.Tandem DSCs, where both cathode and anode are sensitized with dye molecules, hold great promise for higher efficiencies than the conventional n-type DSCs. 1-5 However, the development of tandem DSCs is limited by the low efficiency of p-type DSCs. Currently, NiO is the semiconductor support used in p-DSCs. It limits the energy conversion efficiency due to its low transparency to the visible light and also its valence band edge. Many dye molecules for p-DSCs suffer from the fast charge recombination between holes in NiO and the reduced dye or I À in the electrolyte. [6][7][8][9] Therefore, developing new p-type semiconductors and sensitizers is the grand challenge in this promising area.Lindquist and co-workers first demonstrated the generation of cathodic photocurrent with an erythrosine-sensitized NiO cathode. 1 Since then, a few other photosensitizers including coumarin, 7,8,10 perylene monoimide 6,11 and porphyrin 9 derivatives have been synthesized. Sun, Hagfeldt and co-workers first reported push-pull dyes with anchoring group on the triphenylamine donor. Solar cells sensitized with those dyes gave high incident photon-to-electron conversion efficiencies (IPCEs). 12-14 More recently, efficient sensitizers consisting of oligothiophene units have been reported, which exhibit long-lived charge separated excited states and have produced the most efficient p-type DSCs so far. 15 In the design of a donor-acceptor dye, the linker group between the donor and the acceptor plays an important role in terms of optical absorption and charge transfer properties, and thus has been widely studied for n-type DSCs. 3,[16][17][18] However, in terms of p-type DSCs, the studies are limited. 12,14 Sun et al. have shown that the phenyl linker in their organic chromophores provides higher IPCE but narrower spectral response than the thiophene linker. 12 Nattestad et al. have varied the length of the oligothiophene bridge in order to control the spatial separation of the photo-generated charge carriers. 15 Among the various linkers, 3,4-ethoxythiophene (EDOT) has been proved to be an excellent bridging ligand in the sensitizers designed for n-type DSCs. 16 The planarity of the dye molecule can facilitate the electron transfer from donor to acceptor. However, to our best knowledge, EDOT has not been reported as a linker in donoracceptor dyes for p-type DSCs. Herein we report three new organic donor-acceptor dyes with different linker groups designed for NiObased p-type DSCs (Scheme 1). The dyes are comprised of triphenylamine as an electron donor and dicyanovinyl as an electron acceptor. We have compared three linkers: phenyl, thienyl, and EDOT groups, and demonstrated that EDOT outperforms the other two linkers. This i...

Dye-sensitized PS- b -P2VP-templated nickel oxide films for photoelectrochemical applications

“…Di-tert-butyl-4,4 0 -((4-(5-formylthiophen-2-yl)phenyl)azanediyl)dibenzoate was synthesized as previously described [41]. FTO-coated glass substrates (1.1 mm thickness; 80 VA 21 ) were purchased from SOLEMS S.A., Palaiseau, France.…”

“…Compound 1 (figure 2 and table 1), containing a triarylamine electron-donor part and an ethyl cyanoacetate electron-acceptor part separated by a thiophene unit, has been prepared in two steps from previously described di-tert-butyl 4,4 0 -((4-(5-formylthiophen-2-yl)phenyl)azanediyl)dibenzoate [41]. The UV-visible absorption spectrum of 1 in CH 3 CN solution displays a typical charge-transfer (CT) band centred at 436 nm (29 300 M 21 cm 21 ).…”

Molecular Level Factors Affecting the Efficiency of Organic Chromophores for p-Type Dye Sensitized Solar Cells

“…At anodic potentials, all chromophores presented a similar oxidation behavior resulting in an oxidation wave having a peak potential at ca. 0.5 V vs. Fc +/˝, which is related to the oxidation of the electron-rich TPA group [29]. The reductive behavior is generally more complex, showing for all dyes a first, weak and irreversible wave likely originated by the reductive chemisorption of the acidic protons onto the electrode surface [30].…”

Developments in and prospects for photocathodic and tandem dye-sensitized solar cells

“…Among the acceptors trialled were 9,10-dicyanoacenaphtho[1,2-b]quinoxaline (DCANQ), dicyanovinylene (DCV) [81,90,[94][95][96][97], tricyanofurane [94] squarine [87,94], bodipy [98] and 1,3-diethyl-2-thioxodihydropyrimidine-4,6-dione (DETB) [82,96].…”