Triplication of the Photocurrent in Dye Solar Cells by Increasing the Elongation of the π‐conjugation in Zn‐Porphyrin Sensitizers

Abstract

Porphyrins are very promising sensitizers for dye solar cells (DSC) but narrow absorption bands at 400-450 and 500-650 IntroductionDye-sensitized solar cells (DSCs) have attracted significant attention as low-cost alternatives to conventional solid-state photovoltaic devices. In these cells, a nanoporous material is filled with a thin layer of a sensitizer which can be photoexcited to ultimately provide a photocurrent.1 Ruthenium-based dyes have been used as the most successful sensitizers to date yielding up to 11.3% solar-to-electric power conversion efficiencies under 1 sun ilumination. 2, 3 However, these dyes lack some of the desired properties required for their large scale production: low raw material costs and a good spectral matching with the solar radiation. Thus, there is real need for the development of inexpensive dyes with improved light absorption in the red and near infrared region. Extended -aromatic molecules have the potential to fulfill these two requirements. [4][5][6][7][8][9] Porphyrins are molecules that contain a heterocylic macrocycle with a -aromatic core. These do not rely on precious metals such as ruthenium and benefit from very high molar extinction coefficients. Metaloporphyrins show an intense Soret band at 400-450 nm and moderate Q bands at 500-650 nm. 10Compared to the ruthenium complexes, these narrow bands limit the light-harvesting properties for porphyrins-based DSC. However, it has been demonstrated that elongation of the conjugation and loss of symmetry causes broadening and a red shift of the absorption bands in porphyrins. 9,11,12 Additionally, they present good photostability and high light-harvesting capabilities that favour applications in thin low cost DSC. In this work we describe the impact of using an oligothienylenevinylene to bridge a Zn-porphyrin system and the anchoring group of the sensitizer. We show that this strategy increases the extended system producing an exceptional absorption enlargement between 450 and 650 nm. This translates into a 3-fold photocurrent increase to reach a cell eff Results and DiscussionA Zn-porphyrin sensitizer with extended absorption was synthesised by the structural combination of the Zn-porphyrin (1) and a previously reported dye containing two oligothienylenevinylene units (2). 13 The structures of these sensitizers (including terminal groups for anchoring to TiO2 surface) are shown in Figure 1. Thus, the Zn-porphyrinoligothienylenevinylene (3) was designed having the main features of 1 and 2 linked by a styryl group. The porphyrins 1 and 3 dyes were prepared by Knoevenagel condensation of the corresponding aldehydes 13 and cyanoacetic acid in 72% and 89% yield, respectively. The oligothienylenevinylene dye (2) was prepared according to a previously described procedure. 13Further details of synthesis methods are given in SI as well as full characterization data.[ Figure 1. Structure of Zn-porphyrin dye (1), oligothienylenevinylene dye (2) and Zn-porphyrin-oligothienylenevinylene dye (3).The electrochemical properties (see ...

New acceptor–π-porphyrin–π-acceptor systems for solution-processed small molecule organic solar cells

“…[10][11][12][13][14][15] Inspired by natural photosynthetic organisms, where chlorophylls absorb light for energy conversion, and because of intense Soret band at around 400 nm and the Q bands close to 600 nm, porphyrins and their derivatives are excellent building blocks for the construction of light harvesting architectures. 16 Porphyrins are among the best sensitizers in Dye Sensitized Solar cells (DSSCs) [17][18][19][20][21][22] showing performances as high as 12%. 23 However, the utilization of porphyrins as active materials in solution-processed BHJ solar cells have been limited [24][25][26][27][28][29][30][31][32][33] despite their natural tendency to form aggregates by π-π stacking interactions.…”

Surface Modification of Zinc Oxide Nanorods with Zn-Porphyrin via Metal-Ligand Coordination for Photovoltaic Applications

“…The obtained HOMO edge is 6.58 eV which is significantly varied from the valence band edge of the pristine ZnO nanorods (7.33 eV, the thin solid line in Figure 3(a)) and the HOMO edge of Zn-porphyrin dye (5.23 eV). 20 This result clearly indicates that the valence states of the ZnO nanorods were strongly influenced by the orbital of the Zn-porphyrin.…”

“…A similar photoluminescence quenching has also been reported for Zn-porphyrin attached to titanium oxide. 20 …”

Synthesis of novel porphyrin and chlorin phosphonic acids and their immobilization on metal oxides

“…All solvents were purified and dried by standard methods. 1 H, 13 Electrodes. The electrodes were prepared following a known procedure [36,37].…”

“…In particular phthalocyanines [6][7][8][9], porphyrins [10][11][12][13], and chlorins immobilized on polycrystalline titanium dioxide were investigated and studied with respect to achieve technically and economically reasonable dye sensitized solar cells [14][15][16][17][18][19][20][21][22][23][24]. For self-assembling on titanium dioxide or similar metal oxide surfaces compounds are required which bear carboxylic-, phosphonic-or sulfonic acid functionalities for covalent linking to the surface.…”