An Organic Dyad Composed of Diathiafulvalene-Functionalized Diketopyrrolopyrrole-Fullerene for Single-Component High-Efficiency Organic Solar Cells.

A new low-band gap dyad DPP-Ful, which consists of covalently linked dithiafulvalene-functionalized diketopyrrolopyrrole as donor and fullerene (C60 ) as the acceptor, has been designed and synthesized. Organic solar cells were successfully constructed using the DPP-Ful dyad as an active layer. This system has a record power-conversion efficiency (PCE) of 2.2 %, which is the highest value when compared to reported single-component organic solar cells.

Near-infrared squaraine co-sensitizer for high-efficiency dye-sensitized solar cells.

A combination of squaraine-based dyes (SPSQ1 and SPSQ2) and a ruthenium-based dye (N3) were chosen as co-sensitizers to construct efficient dye-sensitized solar cells. The co-sensitization of squaraine dyes with N3 enhanced their light-harvesting properties as a result of the broad spectral coverage in the region 350-800 nm. The co-sensitized solar cells based on SPSQ2 + N3 showed the highest short circuit current density of 17.10 mA cm(-2), an open circuit voltage of 0.66 V and a fill factor of 0.73, resulting in the highest power conversion efficiency of 8.2%, which is higher than that of the dye-sensitized solar cells based on the individual SPSQ1 and SPSQ2 dyes. The high power conversion efficiency of SPSQ2 + N3 was ascribed to its good light-harvesting properties, which resulted from its broader incident photon current conversion spectrum than that of the individual dyes. The high electron life time and electron recombination, which were the main causes of the higher efficiency of the device, were successfully analysed and correlated using transient absorption spectrometry and intensity-modulated photovoltage spectrometry.

Highly Directional 1D Supramolecular Assembly of New Diketopyrrolopyrrole-Based Gel for Organic Solar Cell Applications.

A new thermoreversible organogel based on diketopyrrolopyrrole dye (DPP-NCO) is reported for the first time and evolved as a new building block for the fabrication of 1D supramolecular assembly. AFM analysis illustrated that its gel state is composed of different sized 1D rods. DPP-NCO gel used as an additive in organic solar cells yields high efficiency of 7.9% owing to better nanophase separation of its active layer.

Near-infrared unsymmetrical blue and green squaraine sensitizers.

Two novel panchromatic asymmetrical squaraine sensitizers (SPSQ1 and SPSQ2) have been synthesized, characterized and effectively used for TiO2-based dye sensitized solar cells. In a solution, both dyes display a highly intense near-IR absorption (SPSQ1; 651 nm and SPSQ2; 692 nm), the red shifted absorption of SPSQ2 was attributed to the incorporation of the auxiliary acceptor dicyanovinyl unit on the squaraine moiety. Interestingly, the dicyanovinyl unit lowered the LUMO level of SPSQ2, which decreased the band gap and red shifted the absorption when compared to SPSQ1. These dyes possess suitable HOMO and LUMO levels to work as efficient sensitizers in DSSCs. The experimental trends in their optical and electrochemical properties are well matched with the theoretical calculations modeled by TDDFT. The blue and green color of the devices showed their complementary absorption and harvest a greater number of photons from solar flux. Under standard global AM 1.5 G solar conditions, the DSSC based on SPSQ2 exhibited a high power conversion efficiency of 3.1% with a high short circuit current density (JSC) attributed to the broadening of the IPCE spectra in the UV-vis and near-IR regions when compared to SPSQ1 (2.5%).

NIR absorbing D-π-A-π-D structured diketopyrrolopyrrole-dithiafulvalene based small molecule for solution processed organic solar cells.

A new low band gap small molecule with a D-π-A-π-D molecular structure composed of a dithiafulvalene (DTF) donor and a diketopyrrolopyrrole (DPP) acceptor was synthesized and tested for organic solar cells. Using the small molecule as an electron donor, and PC71BM as an acceptor a high power conversion efficiency (PCE) of 4.3% was achieved.

Organic dyes containing carbazole as donor and π-linker: optical, electrochemical, and photovoltaic properties.

A series of new metal free organic dyes containing carbazole as donor and π-linker have been synthesized and characterized as effective sensitizers for dye sensitized solar cells (DSSCs). The carbazole functionalized at C-2 and C-7 served as electron-rich bridge. The donor property of the carbazole is substantially enhanced on introduction of tert-butyl groups at C-3 and C-6 positions and the oxidation propensity of the dyes increased on insertion of thiophene unit in the conjugation pathway. These structural modifications fine-tuned the optical and electrochemical properties of the dyes. Additionally, the presence of tert-butyl groups on the carbazole nucleus minimized the intermolecular interactions which benefited the performance of DSSCs. The dyes served as efficient sensitizers in DSSCs owing to their promising optical and electrochemical properties. The efficiency of DSSCs utilizing these dyes as sensitizers ranged from 4.22 to 6.04%. The tert-butyl groups were found to suppress the recombination of injected electrons which contributed to the increment in the photocurrent generation (JSC) and open circuit voltage (VOC). A dye with carbazole donor functionalized with tert-butyl groups and the conjugation bridge composed of 2,7-disubstituted carbazole and thiophene fragments exhibited higher VOC value. However, the best device efficiency was observed for a dye with unsubstituted carbazole donor and the π-linker featuring carbazole and bithiophene units due to the high photocurrent generation arising from the facile injection of photogenerated electrons into the conduction band of titanium dioxide (TiO2) facilitated by the low-lying LUMO.

Solution processable indoloquinoxaline derivatives containing bulky polyaromatic hydrocarbons: synthesis, optical spectra, and electroluminescence.

New hybrid materials featuring the dipolar fragment 6H-indolo[2,3-b]quinoxaline attached to the bulkier polyaromatic hydrocarbons such as fluoranthene, triphenylene, or polyphenylated benzene have been synthesized by a two-step procedure involving Sonogashira and Diels-Alder reactions. They were characterized by absorption, emission, electrochemical, thermal, and theoretical investigations. The electronic properties of the compounds were dominated by the 6H-indolo[2,3-b]quinoxaline chromophore, and the incorporation of polyaromatic hydrocarbons reduces the chances of nonradiative deactivation processes associated with the excited state and improves the emission properties. The compounds displayed cyan emission with moderate quantum efficiency when excited at the absorption maximum. All of the compounds exhibited an irreversible reduction process corresponding to the addition of electron at the quinoxaline segment. They showed moderate thermal stability and glass transition temperature greater than 100 °C. The presence of rigid 6H-indolo[2,3-b]quinoxaline and bulkier polyaromatic hydrocarbon segments enhances the thermal stability and glass transition temperature significantly. Finally, the dyes were successfully applied as an electron-transporting and emitting layer in multilayered organic light-emitting diodes comprising a N,N'-bis(l-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine hole-transporting layer. The cyan emitting devices were characterized by moderate device performance parameters.