Abstract We prepared a series of four new diketopyrrolopyrroles (DPPs)‐based sensitizers that exhibit high‐molar extinction coefficients, extended absorption into the long wavelengths, and well‐suited photoredox properties to act as sensitizers in p‐type dye‐sensitized solar cells (p‐DSSCs). These new DPP dyes, composed of a thienyl DPP core, are substituted on one end either by a thiophene carboxylic (Th) or a 4,4′‐[(phenyl)aza]dibenzoic acid as anchoring group and, on the other extremity, either by a proton or a naphthalene diimide (NDI) moiety. These new dyes were completely characterized by absorption and emission spectroscopy along with electrochemistry and they were modeled by time‐dependent DFT (TD‐DFT) quantum chemical calculations. The photovoltaic study in p‐DSSC with iodine‐based electrolyte reveals that the Th‐DPP‐NDI dye is particularly efficient ( J sc =7.38 mA cm −2 ; V oc =147 mV; FF=0.32; η =0.35 %) and quite active in the low‐energy region of the solar spectrum (above 700 nm), where only a few NiO dyes are effective. To illustrate the potential of DPP dyes in photocathodes, we designed a highly efficient tandem DSSC composed of a TiO 2 photoanode sensitized by the dye D35 and a NiO photocathode sensitized by Th‐DPP‐NDI. This tandem DSSC gives the highest performances ever reported ( J sc =6.73 mA cm −2 ; V oc =910 mV; η =4.1 %) and, importantly, the tandem cell outcompetes with the sub‐cells.
Dye-Sensitized Solar Cells (DSSCs) belong to the next generation of photovoltaic technologies. They are advantageous, because in DSSCs both photon harvesting and charge separation and collection occur in the active area of the cell. Additionally, the dye wavelength-selective absorption flexibility extends up the near-IR, driving towards transparent applications [1]. We have already introduced and characterized using the fs-Transient Absorption technique, the near-IR cyanine sensitizer VG20 that strongly absorbs at 830 nm (ε=154'000 M-1cm-1) when adsorbed on TiO2 [2]. After optimization and use of the de-aggregating agent CDCA, as well as electrolyte additives to tune the SC energy, VG20 exhibited the record, by the time, product of PCE efficiency (3.1%) and Average Visible Transmission (AVT) of 75% with injection occurring in 2-4 ps. The temporal competition of energy transfer (ET) from monomers to aggregates limits the injection efficiency to 30%. Herein, we report two novel pyrrolopyrrole cyanine dyes (TB207, TB423) designed to strongly absorb in the near-IR and hinder the aggregate formation upon sensitization. Both absorb at ~760 nm (ε~138'000 M-1cm-1) in solution and when incorporated in real DSSCs cover the 650-850 nm region. By the successful combination of fs-fluorescence and fs-transient absorption set-ups in solution, in non-injecting Al2O3 DSSCs and injecting TiO2 DSSCs, it was identified for TB207 that both the injection and ET occur in a distribution of times (2-23 ps) due to the inhomogeneity of the system. The total PCE reached 4.2% for TB207, with AVT 74% and injection efficiency to be 40-60%, while for TB423 the injection efficiency reached 80%. Interestingly, for the latter no pronounced dependence on the aggregate concentrations was recorded indicating possible secondary high yield injection from aggregates. Finally, the next experiments are focusing on new promising dyes designed to overcome limitation issues with target the optimization towards transparent and colourless devices. [1] F. Grifoni et al., Adv. Energy Mat., 2021, 2101598, 1-47 [2] W. Naim et al., JACS Au, 2021, 2021, 1, 4, 409–426
Using the HETPHEN approach, five new heteroleptic copper(I) complexes composed of a push-pull 4,4'-styryl-6,6'-dimethyl-2,2'-bipyridine ligand and a bulky bis[(2-diphenylphosphino)phenyl]-ether (DPEphos) or a bis2,9-mesityl phenanthroline (Mes2Phen) were prepared and characterized by electronic absorption spectroscopy, electrochemistry, and TD-DFT calculations. These complexes exhibit very intense absorption bands in the visible region with extinction coefficient in the range of 5-7 × 10(4) M(-1) cm(-1). The analysis of the position, intensity and band shape indicates a strong contribution from an intra-ligand charge-transfer transition centered on the styrylbipyridine ligand along with MLCT transitions. These new complexes experimentally demonstrate that good light harvesting properties with bis-diimine copper(I) complexes are a reality if one chooses suitable ligands in the coordination sphere. This constitutes a milestone towards using bis-diimine copper(I) complexes for solar energy conversion (artificial photosynthesis and solar cells).
Although justly considered as a cumbersome component in artificial photosystems, these simple molecules are a “necessary evil” to drive photo-induced reactions aiming at producing high added value molecules by photo-induced reduction of low energy value substrates. This review first presents the specifications of sacrificial electron donors. Then the various families of sacrificial donors used from the early 1970s to nowadays are reviewed, such as aliphatic and aromatic amines, benzyl-dihydronicotinamide (BNAH), dimethylphenylbenzimidazoline (BIH), ascorbic acid, oxalate and finally thiols. Experimental conditions (pH, solvent) are immensely versatile but important trends are given for adequate operation of a three-component system. Although literature abounds with various, very different artificial photosystems, we will realize that virtually the same sacrificial donors are used over and over again. Dans le domaine de la photosynthèse artificielle, les donneurs d’électron sacrificiels sont un mal nécessaire, permettant de produire des molécules à haute valeur ajoutée à partir de molécules à faible contenu énergétique, en alimentant les photosystèmes artificiels en électrons. Cet article passe en revue les différents donneurs sacrificiels utilisés par la communauté scientifique depuis les années 1970 jusqu’à nos jours. Les amines, les thiols, les modèles du NADH sont ainsi, entre autres, répertoriés ainsi que leurs conditions d’utilisation optimales.
