Investigation on the Trap Signature in Organic Semiconductor Turmeric Film Through Current-Voltage Analysis

The analytical description of the trap signature in the charge conduction process of turmeric dye-based organic semiconductor has been presented in this study.An analytical explanation of the built-in potential Ⅴx-Ⅴ graph that emphasizes the presence of trapping states has been provided.Differential analysis of current-voltage(Ⅰ-Ⅴ)characteristics has also been conducted to verify the trap signature of the carrier in the device.The non-monotonous decrement of the G(Ⅴ)-Ⅴ plot verifies the trap signature.The values of trap energy(Et)and trap factor(θ)have been derived from the logarithmic Ⅰ-Ⅴ relationship.From the analysis of the semilogarithmic Ⅰ-Ⅴ plot,the barrier height(ϕbi)of the device has also been determined.The overallⅠ-Ⅴcurve has been taken into account to examine the Richardson-Schottky and Poole-Frenkel effects on the trap-assisted charge conduction process.From the results of the experiment,the Schottky effect has been observed to be effective,which leads to a bulk-limited charge conduction process.

Substrate temperature dependent studies on properties of chemical spray pyrolysis deposited CdS thin films for solar cell applications

Thin films of CdS have been prepared by chemical spray pyrolysis by spraying precursor solution directly onto soda lime glass（SLG） substrates. Influence of substrate temperature on structural, optical, morphological and electrical properties have been investigated by using various techniques such as low angle X-ray diffraction（XRD）, Raman spectroscopy, X-ray photoelectron spectroscopy（XPS）, field emission scanning electron microscopy（FESEM）, atomic force microscopy（AFM）, transmission electron microscopy（TEM）, UV–visible spectroscopy photoluminescence（PL） spectroscopy etc. Formation of CdS has been confirmed by low angle XRD,Raman spectroscopy and XPS analysis. XRD pattern showed that CdS films are polycrystalline, have hexagonal structure and prefer orientation of crystallites shifts from（101） to（002） with increase in substrate temperature.Raman spectroscopy revealed that exciton-phonon coupling depends on substrate temperature and hence on crystallite size. Optical band gap increased from 2.43 to 2.99 eV when substrate temperature increased from 325 to 475 ℃. Transmittance of the film also showed an increasing trend from 52% to 80% with increase in substrate temperature. Such high band gap and transmittance values of CdS films prepared at 475℃ make it a useful window material in CdS/CdTe and CdS/Cu_2S heterojunction solar cells.

Low substrate temperature deposition of transparent and conducting ZnO:Al thin films by RF magnetron sputtering

Transparent and conducting Al-doped ZnO（ZnO：Al） films were prepared on glass substrate using the RF sputtering method at different substrate temperatures from room temperature（RT） to 200 ℃. The structural,morphological, electrical and optical properties of these films were investigated using a variety of characterization techniques such as low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy（XPS）, field-emission scanning electron microscopy（FE-SEM）, Hall measurement and UV–visible spectroscopy. The electrical properties showed that films deposited at RT have the lowest resistivity and it increases with an increase in the substrate temperature whereas carrier mobility and concentration decrease with an increase in substrate temperature. Low angle XRD and Raman spectroscopy analysis reavealed that films are highly crystalline with a hexagonal wurtzite structure and a preferred orientation along the c-axis. The FE-SEM analysis showed that the surface morphology of films is strongly dependent on the substrate temperature. The band gap decreases from 3.36 to 3.29 e V as the substrate temperature is increased from RT to 200 ℃. The fundamental absorption edge in the UV region shifts towards a longer wavelength with an increase in substrate temperature and be attributed to the Burstein-Moss shift. The synthesized films showed an average transmission（〉 85%） in the visible region, which signifies that synthesized ZnO：Al films can be suitable for display devices and solar cells as transparent electrodes.

All-carbon nanotube diode and solar cell statistically formed from macroscopic network

Schottky diodes and solar cells are statistically created in the contact area between two macroscopic films of single-walled carbon nanotubes （SWNTs） at the junction of semiconducting and quasi-metallic bundles consisting of several high quality tubes. The n-doping of one of the films allows for photovoltaic action, owing to an increase in the built-in potential at the bundle-to-bundle interface. Statistical analysis demonstrates that the Schottky barrier device contributes significantly to the I-V characteristics, compared to the p-n diode. The upper limit of photovoltaic conversion efficiency has been estimated at N20%, demonstrating that the light energy conversion is very efficient for such a unique solar cell. While there have been multiple studies on rectifying SWNT diodes in the nanoscale environment, this is the first report of a macroscopic all-carbon nanotube diode and solar cell.