Low-cost solar cells have been the subject of intensive research activities for over half century ago. More recently, dye-sensitized solar cells (DSSCs) emerged as a new class of low-cost solar cells that can be easily prepared. Natural-dye-sensitized solar cells (NDSSCs) are shown to be excellent examples of mimicking photosynthesis. The NDSSC acts as a green energy generator in which dyes molecules adsorbed to nanocrystalline layer of wide bandgap semiconductor material harvest photons. In this paper we investigate the structural, optical, electrical, and photovoltaic characterization of two types of natural dyes, namely, the Bahraini Henna and the Yemeni Henna, extracted using the Soxhlet extractor. Solar cells from both materials were prepared and characterized. It was found that the levels of open-circuit voltage and short-circuit current are concentration dependent. Further suggestions to improve the efficiency of NDSSC are discussed.
Hydrogenated amorphous silicon-selenium alloy thin films were prepared by the decomposition of SiH4 and H2Se gas mixtures in a radio-frequency plasma glow discharge at a substrate temperature of 250 °C. The alloy composition was varied by changing the gas volume ratio Rv = {[H2Se]/[SiH4]}. Infrared and Raman spectroscopies were used to probe the bonding structure of the material. In addition to the hydrogen induced bands normally observed in a-Si:H, a new selenium induced band at 390 cm−1, assigned to the stretching mode of the Si—Se bond, was observed. Analysis of the vibrational SiH stretching region reveals the presence of a significant level of (Si)xSe3−xSiH and (Si)ySe2−ySiH2 configurations. Optical and electrical measurements show that increasing the selenium content results in an increase in the optical (Tauc) gap and a decrease in the dark conductivity (σD) and photoconductivity (σph). However, the photosensitivity (σph/σD) remains high for the entire composition range. The Urbach energy and defect density were obtained from subgap absorption measurements. Upon increasing the Se content, a broadening of the band tails and an increase in the defect density were observed. The photoluminescence intensity and width at half-maximum data for the alloys are consistent with the results drawn from the optical absorption measurements.
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