Abstract
Solar cells thin films were prepared using polyvinyl alcohol (PVA) as a thin film, with extract of natural pigment from local flower. A concentration of 0.1g/ml of polyvinyl alcohol solution in water was prepared for four samples, with various concentrations of plant pigment (0, 15, 25 and 50) % added to each of the four solutions separately for preparing (PVA with low concentrated dye , PVA with medium concentrated dye and PVA with high concentrated dye ) thin films respectively . Ultraviolet absorption regions were obtained by computerized UV-Visible (CECIL 2700). Optical properties including (absorbance, reflectance, absorption coefficient, energy gap and dielectric constant) via UV- Vis were tested, too. Fourier transform infrared (FTIR) spectrophotometer was employed to test the samples. Thermal analysis of thin films, including melting point (Tm), onset degree, endset degree, and crystallinity% were tested by differential scanning calorimeter (DSC). Three dimensional morphologies of thin films were inspected by atomic force microscopy (ATM). Contact angle also was tested as an index to hydrophilicity. Results proved that the ultraviolet and FTIR absorption increase after adding the natural pigment to PVA thin film, as well as it increases with increasing concentration of natural pigment. DSC analysis revealed an increase of PVA melting point when adding 15% concentration and it decreases with a 50% concentration of pigment. AFM results show an increase in surface roughness, hence the surface bearing index of PVA thin films is inversely proportional to pigment concentration. Contact angle decreases from 46.5° for pure PVA thin film to 44. 8°, 42. 6° and 35.2° after adding (15, 25, and 50)% concentration of natural dye respectively. Optical properties were enhanced by adding the natural dye, hence energy gap decreased from 3 eV for pure PVA to 2.3 eV for the PVA with a high concentrate dye. Dielectric constant increased with increasing concentration of dye, which leads to high polarization of solar cell.
Highlights
Materials are classified according to their wetting behavior into two categories: hydrophobic and hydrophilic, the former have a surface with sturdy affinity to water whereas the latter fend off water
The traditional polymer solar cells, known as all polymer solar cells (APSC)have long been used in the last few decades, they haven’t gained the desired high performance compared to their new counterparts, manufactured by modern techniques, due to many challenges: the poor polymer-polymer miscibility may lead to a high phase segregation between donor-acceptor, which enhances short circuit current density ( JSC), and fill factor, decreasing efficiency of solar cells [4].The efficiency of polymer solar cells is affected by the diffusion length of the exaction, i.e. the distance travelled by exactions until being recombined, which is in the range [3,4,5,6,7,8,9,10] nm in organic semiconductors
Absorption coefficient Absorption coefficient calculated according to Eq 1, Fig 2.d shows the absorption coefficient of all samples as shown below: Figure 2.b The Absorbance of polyvinyl alcohol (PVA) Thin Films HCD: high concentration dye, MCD: medium concentration dye, LCD: low concentration dye Reflectance: Fig 2.c shows the reflectance of all samples as shown below, as they are obtained by the UV
Summary
Materials are classified according to their wetting behavior into two categories: hydrophobic and hydrophilic, the former have a surface with sturdy affinity to water whereas the latter fend off water. The exactions taking place in a large distance from the hetero junction are difficult to be gained, which impedes the efficiency of the solar cell due to the thin layer near the interface which may not be sufficient to make use of solar radiation [5] Another issue associated with organic semiconductors is the speed through which the exaction is generated and moved to the donor to acceptor being dissociated in the diffusion length, and this doesn’t directly creates free charge carriers due to Coulomb attraction. Mango leaf extract dye is environmental friendly, non toxic ,cheap, available and active dye for solar cell fabricated under different conditions
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