•Three novel organic dyes with fused tetracyclic donor were designed for DSSCs.•The nonplanar conformation of the dyes can impede dye aggregation.•The effect of π-linkers on the photovoltaic properties of the dyes was evaluated.•An attractive PCE up to 7.54% has been achieved.Novel metal-free organic dyes based on polycyclic aromatic donor, pyrrolo[3,2,1-kl]phenothiazine, have been synthesized and applied in dye-sensitized solar cells. Combined with cyanoacrylic acid as the acceptor/anchoring group and simple π-spacers such as thiophene (JY40), furan (JY41), and terthiophene (JY42) as the conjugated linker, these dyes show good power conversion efficiency (PCE). The photophysical, electrochemical and photovoltaic properties, as well as theoretical calculations of these dyes were fully investigated. An attractive PCE up to 7.54%, with a short-circuit photocurrent density (Jsc) of 17.76 mA cm−2, an open-circuit photovoltage (Voc) of 726 mV, and a fill factor (FF) of 0.58 has been achieved by the JY42-based cell under standard AM 1.5 G irradiation in conjunction with an iodine electrolyte.Download high-res image (180KB)Download full-size image

A series of zinc porphyrin dyes (JY24–27) featured phenothiazine moieties have been synthesized and applied as photosensitizers in dye-sensitized solar cells. The phenothiazine donors were directly attached to the meso-position of porphyrins, and different π-linkers (benzene, thiophene and ethynyl benzene) and acceptor groups (carboxylic acid and cyanoacrylic acid) were applied to tune the photoelectric properties of these push–pull porphyrin dyes. The photophysical, electrochemical and theoretical studies revealed that the synthesized porphyrin dyes were all capable of being used as photosensitizer. The dye JY27 with an extended conjugation by introducing ethynyl group exhibited a broader absorption region and more significantly improved IPCE values between 550 and 750 nm than the other three dyes, which ensured a good light-harvesting ability and a high short-circuit current density of 15.3 mA cm−2. Finally, JY27-based cell achieved a high efficiency of 6.25% under standard simulated irradiation.

A novel double D–π–A branched dye (JY07) was synthesized and applied as a sensitizer for DSSCs. JY07 exhibited broader and stronger light absorption capability than the single D–π–A dye (JY06). In the meantime, the orthogonal conformation of JY07 was found to be favorable for impeding intermolecular aggregation. Consequently, a power conversion efficiency of 5.33% was achieved under AM 1.5G conditions.

A novel class of metal-free organic dyes based on benzo[a]carbazole have been designed, synthesized, and used in dye-sensitized solar cells for the first time. These types of dyes consisted of a cyanoacrylic acid moiety as the electron acceptor/anchoring group and different electron-rich spacers such as thiophene (JY21), furan (JY22), and oligothiophene (JY23) as the π-linkers. The photophysical, electrochemical, and photovoltaic properties, as well as theoretical calculations of these dyes were investigated. The photovoltaic performances of these dyes were found to be highly relevant to the π-conjugated linkers. In particular, dye JY23 exhibited a broad IPCE response with a photocurrent signal up to about 740 nm covering the most region of the UV–visible light. A DSSC based on JY23 showed the best photovoltaic performance with a Jsc of 14.8 mA cm–2, a Voc of 744 mV, and a FF of 0.68, achieving a power conversion efficiency of 7.54% under standard AM 1.5 G irradiation.Keywords: benzo[a]carbazole; conjugated linkers; dye-sensitized solar cells; intramolecular charge transfer; organic dyes;

An efficient and general Fe(OTf)3-mediated oxidative coupling method was developed for the synthesis of doubly or triply linked porphyrin dimers. Besides the central metal and peripheral substituent, regioselectivity of the oxidative coupling was found to be closely relevant to the onset oxidation potential of the porphyrin substrate, and the reactant with higher Eonset(ox) tends to generate meso-β doubly fused porphyrin dimer.

Three meso-2′-linked porphyrin–BODIPY hybrids which contain one, two, and four BODIPY units (BDP–ZnP, 2BDP–ZnP, and 4BDP–ZnP), respectively, were synthesized. Their photophysical properties were investigated by UV-vis and fluorescence spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy, as well as by theoretical calculations. The electronic properties of the constituent chromophores were found to be largely retained in these hybrids. Meanwhile, efficient and rapid energy transfers from 1BDP* to ZnP were evaluated to be 1.2 × 1011, 1.5 × 1011, and 1.1 × 1011 s−1, respectively.

•Tetraindole-based organic dyes have been synthesized for the first time.•The saddle-shaped structure is favourable for suppressing the dye aggregation.•The dye with a bithiophene as the π-bridge exhibited better performances.•An efficiency up to 6.46% has been achieved with a high Voc of 762 mV.Two new metal-free organic dyes which consist of a saddle-shaped tetraindole donor, a cyanoacrylic acid acceptor/anchoring group and a thiophene or bithiophene π-bridge have been successfully designed and synthesized for dye-sensitized solar cells. The two dyes showed good photoelectric properties, and the saddle-shaped structure of the tetraindole unit was found to be favorable for preventing intermolecular aggregation and enhancing the photovoltage. The two tetraindole-based dyes exhibited good photovoltaic performances in solar cells. An efficiency up to 6.46% with a high open-circuit photovoltage of 762 mV was achieved for the dye JY15 with a 2,2′-bithiophene moiety as the π-bridge using an iodine electrolyte under standard conditions.

•Two novel donor-π-acceptor type organic dyes based on triazatruxene were designed and synthesized for DSSCs.•Rhodanine-3-acetic acid was introduced into triazatruxene-based dyes as electron acceptor for the first time.•The dyes exhibited broad IPCE responses up to 800 nm covering almost the whole visible light spectrum.Two novel triazatruxene-based organic dyes with a rhodanine acceptor have been designed, synthesized, and applied as photosensitizers for dye-sensitized solar cells. The photophysical and electrochemical properties of the dyes were investigated using UV–vis absorption spectroscopy, electrochemistry, and density functional theory calculations. Dyes with π-conjugated spacers, thiophene and benzene, both showed broad IPCE responses even up to 800 nm which covers almost the whole visible light spectrum and offers great potential in DSSCs. An overall conversion efficiency of 3.60% under AM 1.5 illumination (100 mW cm−2) was achieved with the benzene spaced dye.

Two novel tri(N-carbazolyl)triphenylamine-based organic dyes were designed, synthesized and applied as photosensitizers for dye-sensitized solar cells. The superiority of the starburst structure of these dyes is suppressing the intermolecular interactions and guaranteeing a fast electron injection into the TiO2 semiconductor. Cyanoacrylic acid and rhodanine-3-acetic acid were separately used as electron acceptors/anchoring groups to compose the photosensitizers. Different acceptors led to striking changes in the photophysical, electrochemical and photovoltaic properties. An overall power conversion efficiency of 6.53% with a short-circuit photocurrent density of 13.4 mA cm−2, an open-circuit photovoltage of 735 mV and a fill factor of 0.66 was achieved by the dye with tri(N-carbazolyl)triphenylamine as the donor and cyanoacrylic acid as the acceptor under AM 1.5 illumination (100 mW cm−2).

A novel class of double D–π–A branched organic dyes based on 2,2′-disubstituted-1H,1′H-3,3′-biindole moiety have been synthesized, characterized and applied as photosensitizers for dye-sensitized solar cells. Their photophysical, electrochemical and photovoltaic properties are further investigated. These type of organic dyes contain two cyanoacrylic acid moieties as electron acceptors/anchoring groups and different electron-rich conjugated linkers such as furan (JY11), thiophene (JY12) and 2,2′-bithiophene (JY13) as π-bridges. The superiority of the cross X-shaped structure of these double D–π–A branched organic dyes is the suppression of the intermolecular interactions and the guarantee of fast electron injection into the TiO2 semiconductor in the dye-sensitized solar cells. A highest power conversion efficiency of 6.54% was achieved for JY13-based cell with an iodine electrolyte under simulated AM 1.5 G solar irradiation (100 mW cm−2).

A simple and efficient method for the meso-functionalization of porphyrin has been developed. Kinetic studies of meso-fluoro-, -chloro-, -bromo-, -iodo-, and -nitro-substituted porphyrins (Ni) with phenol reveal that the reaction undergoes a typical aromatic nucleophilic substitution (SNAr) process. This catalyst-free method can be performed with meso-brominated porphyrins and oxygen-, sulfur-, and carbon-based nucleophiles to achieve a wide variety of meso-substituted porphyrins.

A simple and efficient method has been developed for the switchable synthesis of directly linked meso-brominated Ni(II) porphyrin dimers through PIFA–BF3·Et2O mediated oxidative coupling. The respective syntheses of meso–meso or meso–β singly, doubly, and triply linked porphyrin dimers can be easily realized with the same reagent system.

A metal-free oxidative cycloaddition reaction of substituted benzamides and alkynes has been developed for the synthesis of isoquinolones by using bis(trifluoracetoxy)iodobenzene (PIFA) and trifluoroacetic acid (TFA). Under mild conditions, a wide variety of isoquinolones were conveniently prepared via oxidative annulation of simple N-methoxybenzamide and diarylacetylene or aryl/alkyl acetylene derivatives in yields up to 87%.

A practical method for the preparation of novel tripodal tris(porphyrinato-urea) TP3 1 was readily achieved. Because of its appreciable preorganized triangular cone-shaped cavity resulting from the intramolecular hydrogen bonds of the tripodal tris-urea backbone, this porphyrin trimer host was found to have a high affinity toward fullerenes to form stable inclusion complexes in solution. A 120-fold binding selectivity toward C70 (Kassoc = 1.81 × 107 M–1) over C60 (Kassoc = 1.51 × 105 M–1) was further achieved in toluene. Moreover, the dissociation of such inclusion complexes can be easily realized by introducing H2PO4–, and recapturing of the fullerene can be achieved after withdrawing H2PO4– by Ca2+. A recyclable process for the inclusion and release of fullerene was therefore built by alternately feeding H2PO4– and Ca2+. Benefiting from this approach, TP3 1 was sequentially applied to isolate C70 from the C60-enriched fullerene mixture successfully.

A new class of organic dyes based on triazatruxene have been designed and synthesized for dye-sensitized solar cells. The photoelectronic properties of these donor-π-acceptor dyes can be tuned by changing π-conjugated linkers. The best performance was found for triazatruxene dye TD1, wherein, with thiophene as the conjugated linker and cyanoacrylic acid as the acceptor, a power conversion efficiency up to 6.10% was achieved.

A novel double D–π–A branched dye (JY07) was synthesized and applied as a sensitizer for DSSCs. JY07 exhibited broader and stronger light absorption capability than the single D–π–A dye (JY06). In the meantime, the orthogonal conformation of JY07 was found to be favorable for impeding intermolecular aggregation. Consequently, a power conversion efficiency of 5.33% was achieved under AM 1.5G conditions.

A simple and efficient method has been developed for the switchable synthesis of directly linked meso-brominated Ni(II) porphyrin dimers through PIFA–BF3·Et2O mediated oxidative coupling. The respective syntheses of meso–meso or meso–β singly, doubly, and triply linked porphyrin dimers can be easily realized with the same reagent system.

An efficient and general Fe(OTf)3-mediated oxidative coupling method was developed for the synthesis of doubly or triply linked porphyrin dimers. Besides the central metal and peripheral substituent, regioselectivity of the oxidative coupling was found to be closely relevant to the onset oxidation potential of the porphyrin substrate, and the reactant with higher Eonset(ox) tends to generate meso-β doubly fused porphyrin dimer.

Three meso-2′-linked porphyrin–BODIPY hybrids which contain one, two, and four BODIPY units (BDP–ZnP, 2BDP–ZnP, and 4BDP–ZnP), respectively, were synthesized. Their photophysical properties were investigated by UV-vis and fluorescence spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy, as well as by theoretical calculations. The electronic properties of the constituent chromophores were found to be largely retained in these hybrids. Meanwhile, efficient and rapid energy transfers from 1BDP* to ZnP were evaluated to be 1.2 × 1011, 1.5 × 1011, and 1.1 × 1011 s−1, respectively.