Suraj Soman

Fine tuning of compact ZnO blocking layers for enhanced photovoltaic performance in ZnO based DSSCs: a detailed insight using β recombination, EIS, OCVD and IMVS techniques

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.

Thiophene-bithiazole based metal-free dye as DSSC sensitizer: Effect of co-adsorbents on photovoltaic efficiency

AbstractA new molecule consisting of a bithiazole chromophore sandwiched between two thiophenes, functionalized with benzothiophene unit at one end and cyanoacrylic acid at the other end (BT1) was synthesized, photophysical properties were studied and employed as a photosensitizer in dye-sensitized solar cells (DSSCs). The molecule exhibited an intense absorption in the UV-visible region with absorption extending up to 500 nm. The ground and excited state potentials of BT1 were calculated to be 1.29 and -0.65 V, respectively vs. NHE using cyclic voltammetry. The ground state energy level is more positive than the triiodide electrolyte and excited state energy level is considerably more negative than the TiO2 satisfying the energetic requirements for a photosensitizer in DSSC. The solar cells fabricated from BT1 exhibited an efficiency of 1.13%. The effect of various co-adsorbents (CDCA,TP1 andTP2) on the DSSC performance was investigated in detail. In the presence of CDCA, the photovoltaic efficiency was enhanced to 1.25%, whereas, in the presence of TP1 and TP2, the efficiency lowered to 0.20% and 0.59%, respectively. The increased efficiency in the presence of CDCA could be attributed to the prevention of the aggregation of dye molecules induced by CDCA. On the other hand, TP1 and TP2 were found to be not as effective as CDCA to prevent aggregation leading to the lowering of photoconversion efficiency. Graphical AbstractA benzothiophene-bithiazole based metal-free sensitizer end-functionalized with cyanoacrylic acid acceptor was synthesized, photophysical properties were studied and used for dye sensitized solar cell (DSSC) application. The effect of various co-adsorbents on the DSSC performance was investigated.

Molecular Systems for Solar H2: Path to a Renewable Future

Driving the global energy system into a sustainable path is progressively becoming a major concern and worldwide policy objective. Fossil fuels serve as the primary energy source for most of the worlds energy requirements. Hydrogen has great potential as an environmentally clean energy fuel and as a way to reduce carbon dioxide emissions. The basic mechanism for natural photosynthesis is described along with different artificial photosynthetic systems, giving special attention to molecular photocatalysts. Emphasis is given to the recent advancements in design and development of bimolecular photocatalysts for the generation of H2. These molecular systems have a key role to play in the next generation of solar fuel devices. GRAPHICAL ABSTRACT

Resurgence of DSCs with copper electrolyte: a detailed investigation of interfacial charge dynamics with cobalt and iodine based electrolytes

Deploying earth abundant copper as a redox mediator in dye-sensitized solar cells (DSCs) has been found to be a very promising strategy to achieve higher photovoltage and power conversion efficiencies in full sun (100 mW cm−2) and in low/diffuse light conditions. Achieving higher photovoltage without compromising photocurrent helped copper electrolyte attract considerable attention among alternate electrolytes currently employed in DSCs. The very small reorganization energy between Cu(I) and Cu(II) and small molecular size helped copper achieve unit regeneration efficiency, with a driving force as low as 100 mV and a high diffusion coefficient (Dn), leading to better diffusion length (Ln) and charge collection efficiency (ηcc). Mass transport issues were also found to be improved for copper electrolytes in comparison with cobalt electrolytes. As it is inert to silver and other electrical contacts used in DSCs and possesses higher mobility even in solid state, copper-based electrolyte is a promising candidate to spearhead the commercialization of dye solar technology. In this regard, a detailed evaluation of internal electron transfer dynamics is highly essential to understand the limiting processes in these devices. In the present study, we performed a comparison between copper, cobalt and iodine electrolytes using the same dye (LEG4), semiconductor (TiO2) and additive concentrations to understand in detail the charge transfer processes leading to higher photoconversion efficiencies and also probe the various deleterious processes taking place in copper devices that provide opportunities to further improve its performance in future.