الفهرس 
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Abstract
Most materials frequently used for photovoltaic applications absorb only photons with energy in the UV/VIS regions. Rare-earth up-conversion materials (UC), which convert long wavelength near-infrared (NIR) photons into shorter wavelength visible photons, have been enticing great acuity in various fields including bio-imaging and photovoltaic applications etc. This research aims to integrate UCNPs (NaYF4:Yb3+/Er3+) with the CdTe quantum dots (QDs) to create a model system for optimized QDs solar cell (QDSSC) in which the QDs can absorb the emitted photons from UCNPs for effective utilization of energy in the NIR region. Therefore high electrical current can be obtained. In this work NaYF4:Yb3+/Er3+ UCNPs and CdTe (QDs) nanoparticles were prepared for solar cell construction. Hexagonal UCNPs of β-NaYF4 co-doped with Yb3+ and Er3+ was directly synthesized via thermal decomposition of metals trifluoroacetate precursors. CdTe QDs were prepared by the organometallic method. The prepared nanomaterials were identified and described by XRD, TEM, Absorption and fluorescence spectroscopy. TEM and XRD revealed that the UC nanocrystals were hexagonal with a size range of around 30 nm. The absorption spectrum clarified the presence of one band at λmax= 980 nm while fluorescence spectrum illustrated the presence of three characteristic emission peaks for UCNPs at max= 539 nm, 548 nm and 658 nm. On the other hand, the CdTe QDs size was in the range of 4±0.2 nm with a spherical shape as observed by TEM. Whereas CdTe nanocrystals were cubic as confirmed by XRD. Furthermore, CdTe QDs had a broad absorption band at λmax=535-600 nm and a sharp emission peak at λmax= 621 nm. The prepared nanomaterials were assembled in the photoelectrode of the QDSSC sandwich structure. The I-V characteristic curve of QDSSC with and without UCNPs was measured under solar simulator illumination (100mW/cm2). The results showed that the conversion efficiency of the QDSSC with a NaYF4: Yb3+, Er3+ UCNPs was significantly improved current and voltage (short circuit current (Isc:(20 mA–open circuit voltage (Voc): 410 mV) as compared to the device without UCNPs (Isc: 11 mA–Voc: 250 mV). This enhancement could be due to the presence of the UCNPs that extend the spectral response range of QDSSCs to the NIR region. This solar cell model could drastically boost up solar cell performance by investing more photons through upconversion of NIR photons to the visible range.