• Energy Research

Two new metal-free organic sensitizers with simplest structural variations have been synthesized for application in nanocrystalline TiO2 sensitized solar cells. The donor-pi-bridge-acceptor (D-pi-A) structure dyes, Y2 and Y3 each designed with three parts, an electron donor unit (substituted phenyl), a linker unit (thiophene), and an anchor unit (cyanoacrylic acid) showed maximal monochromatic incident photon to current conversion efficiencies (IPCE) in a device reaching upto 67% and 82% respectively. The organic sensitizers with 3,4,5-trimethoxy phenyl (Y3) as donor moieties obtained better solar light to electrical energy conversion efficiencies of 3.30% where as the organic sensitizer with 2,4-difluoro phenyl as donor (Y2) showed comparatively lower efficiency of 1.02%. The efficiency obtained with the reference sensitizer N719 under similar fabrication and evaluation conditions was 5.84%.

AbstractA new additional benzothiazole (BT) acceptor has been introduced into metal‐free organic dyes (MCG1–MCG4) to construct donor–acceptor–π–acceptor (D‐A‐π‐A) architecture with the systematic replacement of diheteroanthracene donors and heteroaromatic π‐bridge components. BT not only facilitates effective electron transfer from the donor to the anchoring group, but also lowers the band gap. The planarity of the sensitizers induces J aggregation on TiO2, causes the redshift on TiO2, and enhances the light‐harvesting efficiency up to λ=750–800 nm. Transient absorption spectroscopy and electrochemical impedance spectroscopy have been used to understand the trends in short‐circuit current (Jsc) and open‐circuit voltage (Voc). Dye MCG4 showed a superior efficiency of 6.46 %. DFT has been complemented with experimentally determined photoelectrochemical properties. These molecules are new and support π‐bridge extension with BT for better performance of D‐A‐π‐A organic sensitizers.

Hole-transporting material (HTM) plays an important role in PSCs. We report a novel and low-cost, bifluorenylidene-based HTM, denoted as sp-35, which achieved a high PCE of 21.59% and demonstrated good long-term stability compared to spiro-OMeTAD.

Abstract In recent years colloidal quantum dots solar cells have been the subject of extensive research. A promising alternative to existing silicon solar cells, quantum dot solar cells are among the candidates for next generation photovoltaic devices. Colloidal quantum dots are attractive in photovoltaics research due to their solution processability which is useful for their integration into various solar cells. Here, we review the recent progresses in various quantum dot solar cells which are prepared from colloidal quantum dots. We discuss the preparation methods, working concepts, advantages and disadvantages of different device architectures. Major topics discussed in this review include integration of colloidal quantum dots in: Schottky solar cells, depleted heterojunction solar cells, extremely thin absorber solar cells, hybrid organic–inorganic solar cells, bulk heterojunction solar cells and quantum dot sensitized solar cells. The review is organized according to the working principle and the architecture of photovoltaic devices.

Five heteroleptic ruthenium complexes having differentβ-diketonato ligands, [Ru(tctpy)(dppd)(NCS)] (1), [Ru(tctpy)(pd)(NCS)] (2), [Ru(tctpy)(tdd)(NCS)] (3), [Ru(tctpy)(mepd)(NCS)] (4), and [Ru(tctpy)(tmhd)(NCS)] (5), where tctpy = 4,4′,4′′-tricarboxy-2,2′:6′,2′′-terpyridine, pd = pentane-2,4-dione, mepd = 3-methylpentane-2,4-dione, tmhd = 2,2,6,6-tetramethylheptane-3,5-dione, tdd = tridecane-6,8-dione, and dppd = 1,3-diphenylpropane-1,3-dione, were synthesized and characterized. These heteroleptic complexes exhibit a broad metal-to-ligand charge transfer absorption band over the whole visible range extending up to 950 nm. The low-energy absorption bands and theE (Ru3+/2+) oxidation potentials in these complexes could be tuned to about 15 nm and 110 mV, respectively, by choosing appropriateβ-diketonate ligands. Molecular orbital calculation of complex1shows that the HOMO is localized on the NCS ligand and the LUMO is localized on the tctpy ligand, which is anchored to the TiO2nanoparticles. Theβ-diketonato-ruthenium(II)-polypyridyl sensitizers, when anchored to nanocrystalline TiO2films for light to electrical energy conversion in regenerative photoelectrochemical cells, achieve efficient sensitization to TiO2electrodes with increasing activity in the order5<4<3≈2<1. Under standard AM 1.5 sunlight, the complex1yielded a short-circuit photocurrent density of 16.7 mA/cm2, an open-circuit voltage of 0.58 V, and a fill factor of 0.64, corresponding to an overall conversion efficiency of 6.2%. A systematic tuning of HOMO energy level shows that an efficient sensitizer should possess a ground-state redox potential value of >+.53 V versus SCE.

Abstract The device performance of the dye-sensitized solar cells (DSSCs) mainly depends on the sensitizers. Ruthenium sensitizers have played a vital role in the DSSCs to improve power conversion efficiency. However, the absorbance spectra of most Ru-sensitizers limited up to 600 nm, which maybe prohibiting further improvement of short-circuit current density (Jsc). To address this problem, TER-HDT was designed and synthesized by incorporating hexyl dithiafulvalene (HDT)-substituted bipyridine as an ancillary ligand and [2,2′:6′,2′'-terpyridine]-4,4′,4′'-tricarboxylic acid as anchoring ligand together. The synthesized TER-HDT was systematically studied and characterized by spectroscopic (proton NMR, Mass analysis), optical (UV-absorbance and photoluminescence), electrochemical and theoretical techniques. The novel sensitizer TER-HDT absorption tailed up to 900 nm, which originated from the enhanced intermolecular charge transfer in conjunction with efficient intra and intermolecular interactions. The HOMO and LUMO energy levels TER-HDT are suitable for electron injection and regeneration which may help to achieve high efficiency.

Herein, we report a novel layered lead bromide, (CH3CH[Formula: see text]N[Formula: see text]Br[Formula: see text](CH[Formula: see text]NH[Formula: see text]PbBr3, where bulky organic cations, (CH3CH[Formula: see text]N[Formula: see text]Br[Formula: see text](CH[Formula: see text]NH[Formula: see text], amino-ethyl triethyl ammonium [aetriea] were not only incorporated between the inorganic layers but also sandwiched within the inorganic [PbBr6][Formula: see text] octahedral layered structure. The UV-Visible, photoluminescence spectroscopy (PL), X-ray diffraction (XRD) and a field-emission scanning electron microscope (FE-SEM) result show that the new perovskitoid has a microrod shape with an estimated bandgap of [Formula: see text]3.05 eV. The structural and optoelectronic properties of the [aetriea]PbBr3perovskitoid were further corroborated by first-principles density functional theory (DFT) calculations. Thermogravimetric analysis (TGA) data show good stability of the [aetriea]PbBr3perovskitoid. Time-resolved photoluminescence (TRPL) decays from new [aetriea]PbBr3perovskitoid showing 6 ns average lifetime. These results suggest that doubly charged cation hybrid perovskite materials are potential candidates for optoelectronic applications.