Search

Dye solar cells (DSCs) are gaining increasing interest since the recent realization of their high-performance potential in low/indoor light environments. Fused conjugated metal-free organic dyes have become a prominent class of dyes used in DSC in recent times by virtue of their better backbone rigidity, efficient charge transport properties, and the opportunity they provide for further structural modifications. Herein, we report the synthesis and characterization of three metal-free D–π–A organic dyes employing indolo[3,2-b]indole as the donor unit. The optical, electrochemical and photovoltaic properties have been analyzed in detail as a function of π-spacers, namely, benzene (IID-1), thiophene (IID-2) and furan (IID-3). Eventually, the best performance was demonstrated by the dye bearing benzene as the π-spacer. The role of recombination in determining the photovoltaic performance as a function of the nature of π-spacers was explored in detail, using various perturbation techniques on the fabricated devices, and compared with the results obtained from molecular orbital calculations.

New solution processable organic donor–π–acceptor dyads 1 and 2 having electron donating phenoxazine and electron accepting oxadiazole groups have been synthesized. Intramolecular electron communication between the donor and acceptor moieties of these dyads was tuned through changing the substitution pattern at the phenylene linker. The photophysical properties of these dyads have been studied in the solution and film states. These dyads showed green fluorescence and exhibited a positive solvatochromism in the emission spectra, which indicates more polar excited states owing to an efficient charge migration from the donor phenoxazine to the acceptor oxadiazole moiety. The electrochemical, morphological and thermal properties were investigated through cyclic voltammetry, thermogravimetric and atomic force microscopy (AFM) analyses. To understand the electronic structure and band gap of these dyads, density functional theory (DFT) calculations have been performed. Furthermore, we have fabricated the solution processed un-doped electroluminescence devices based on these dyads, which exhibited efficient green emission with Commission Internationale de l’Eclairage (CIE) coordinates of (0.26, 0.49) and (0.27, 0.47) for 1 and 2, respectively, with a luminance maximum of ca. 1751 cd m−2 for the dyad 1, thereby demonstrating its use in organic light emitting diodes (OLEDS).

The electron–hole recombination and back electron flow at the conducting oxide–mesoporous film interface in dye-sensitized solar cells (DSSCs) are addressed primarily by the use of pre-blocking layers. Herein, the effects of zinc oxide (ZnO) blocking layers (BLs) on the photovoltaic performance of ZnO based DSSCs are investigated in detail using electrochemical impedance spectroscopy (EIS), open circuit voltage decay (OCVD) and intensity modulated photovoltage spectroscopic (IMVS) techniques. BLs of varying thicknesses obtained by a low temperature solution process provided uniform surface coverage of nanosized ZnO particles over FTO. Devices with optimized ZnO blocking layer thickness (12 nm) lead to improved performance (efficiency 2.57%) in comparison to the devices fabricated using bare FTO (1.27%) by suppressing interfacial recombination at the FTO/ZnO interface thereby improving the lifetime leading to better performance.