Johns Naduvath

Dye Sensitized Solar Cells: A Review

The development of dye sensitized solar cells (DSSCs), which have derived inspiration from photosynthesis, has opened up exciting new possibilities and paradigms for producing solar photovoltaics possibly at lower cost. The dye-sensitized solar cells with moderate power conversion (∼10%) efficiencies can be manufactured under regular lab conditions without needing clean rooms or very specialized facilities. The entire processing need not involve even a single vapour deposition step. The DSSCs can be considered to be electrochemical devices consisting of (a) a photoanode which has a thick film of a wide band gap oxide semiconductor (like TiO2), typically coated on a transparent conductive oxide (TCO) glass substrate, with TiO2 being sensitized with adsorbed dyes that absorb visible light, (b) an electrolyte that establishes the internal electrical continuity between anode and counter electrode and mainly plays the role of regenerating the dye such that the photoexcitation, electron injection and current flow continues, (c) the counter electrode which is also usually a TCO coated transparent substrate with a suitable catalytic material deposited over it to facilitate efficient charge (electron) transfer from external connection to the electrolyte, (d) sealants to seal the cell assembly containing the electrolyte and prevent ingress of atmospheric influences that may interfere with functioning of the DSSC. The present review describes research that has been carried out and continues on various aspects of DSSCs including developing greater understanding of the basic mechanisms involved, use of new materials, processing techniques and their impact on performance of the cells. A number of challenges are yet to be overcome to realize commercialization of the DSSCs which appears imminent in the near future.

Low temperature thermopower and electrical conductivity in highly conductive CuInO2 thin films

This is the first report on the detailed study on low temperature (6–300 K) electrical conductivity and Seebeck coefficient on copper indium oxide polycrystalline thin films deposited on soda lime glass substrates by a reactive evaporation method. These films, characterized using various experimental techniques, show the highest electrical conductivity (20 to 125 S cm−1) reported to date as well as n- and p- type conductivity. The electrical conductivity mechanisms, based on Motts, Setos and Arrhenius models, in different temperature regimes, comprise of variable range hopping, grain boundary effect and activated thermal conduction. Most interestingly, the thin films manifest a high thermoelectric power factor and absorption in the UV region, indicating their potential in thermoelectric and UV energy conversion device fabrication, respectively.

Electrochemical Synthesis of Novel Zn-Doped TiO2 Nanotube/ZnO Nanoflake Heterostructure with Enhanced DSSC Efficiency

The paper reports the fabrication of Zn-doped TiO2 nanotubes (Zn-TONT)/ZnO nanoflakes heterostructure for the first time, which shows improved performance as a photoanode in dye-sensitized solar cell (DSSC). The layered structure of this novel nanoporous structure has been analyzed unambiguously by Rutherford backscattering spectroscopy, scanning electron microscopy, and X-ray diffractometer. The cell using the heterostructure as photoanode manifests an enhancement of about an order in the magnitude of the short circuit current and a seven-fold increase in efficiency, over pure TiO2 photoanodes. Characterizations further reveal that the Zn-TONT is preferentially oriented in [001] direction and there is a Ti metal-depleted interface layer which leads to better band alignment in DSSC.Graphical Abstract

Effect of Nanograss and Annealing Temperature on TiO2 Nanotubes Based Dye Sensitized Solar Cells

In TiO2 nanoparticle based dye sensitized solar cells (DSSC), the electron injected from the dye has to cross multiple interparticle boundaries in random directions before reaching the electrode. For application in DSSCs, the directional pathway for electron transport through the nanotubes is known to reduce the recombination rate. In the present study, titania nanotubes with nanograss layer have been fabricated by anodization of titanium foil in fluoride containing organic electrolyte. Dye sensitized solar cells with photoanode made of titania nanotubes covered with nanograsswas found to have a higher efficiency than ones made with only titania nanotubes of the same length.This can be attributed to enhanced dye adsorption on nanotubes with nanograss. The efficiency of DSSC using titania nanotubes is also affected by the annealing conditions such as duration, temperature.

Effect of deposition parameters and strontium doping on characteristics of nanostructured ZnO thin film by chemical bath deposition method

Polycrystalline thin films of ZnO and Sr-doped ZnO (ZnO:Sr) on ultrasonically cleaned soda lime glass substrates are synthesized through successive ionic layer adsorption and reaction. The XRD profiles of ZnO and ZnO:Sr films prepared at different number of deposition cycles exhibit hexagonal wurtzite structure with preferred orientation along (002) direction. The crystallites are found to be nano sized, having variation in size with the increase in number of depositions cycles and also with Sr doping. Optical absorbance studies reveal a systematically controllable blueshift in band gap of Sr-doped ZnO films. SEM images indicate enhanced assembling of crystallites to form elongated rods as number of dips increased in Sr doped ZnO. The films are found to be n-type with the Sr doping having little effect on the electrical properties.