Abstract:

A mathematical model that estimates the size dependent optical wavelength of spherical Quantum Dots QDs is presented. The simple model was used for numerical simulation of optical properties of selected QDs and the result obtained strongly agrees with the experimental result. Thus the observed spectra for the considered QDs indicated a blue shift in the absorbance. Comparing the change in the absorbance of QDs to the solar spectrum, it was found that CdSe and CdS of group II-VI QDs show absorbance in the range of ultra violet UV to Infrared (IR) while ZnS exhibited wide optical transmittance ranging from visible vis to deep IR.  In the group III-V, when InSb is varied from 1.58nm to 4.78nm wavelengths from 400nm to 2500nm was observed which covered the whole vis to IR. However varying InAs from 2.02nm to 9.53nm wavelengths ranging from 300nm to 2500nm was observed covering significant portion of UV and near IR. It is found also that in the group III-V when GaAs is varied from 1.5nm to 800nm, wavelengths covering the whole UV to visible spectra were observed with a significant portion of IR. The PbS, PbSe and PbTe of group IV-VI exhibited exceptional optical absorbance that could be tuned in broad range of UV to deep IR which makes them excellent materials for photovoltaic application and IR detectors. Thus stacking QDs of appropriate sizes onto one another in orderly manner, multi junction solar cell which enables absorption and utilization of solar energies over a wide range was modeled. Theoretically, the efficiency in these cells could potentially reach above 60%. Among QDs considered it is found that PbSe and PbTe have the smallest sizes for QD solar cell spectrum.