Seite - 193 - in Photovoltaic Materials and Electronic Devices

photons, the spectral response of the reference cell drops abruptly at 868 nm corresponding to the band gap energy of GaAs (1.42 eV). In the meantime, the photo-response from pin-GaAs/n+-Si recovers a proportion of the below GaAs band gap photons to an extent of up to 1200 nm. The observed enhancement is due to photocarriers generated by silicon substrate. Figure 6. Spectral response of (a) pin-GaAs/ n+-Si with QDs (red); (b) pin-GaAs/n+-Si without QDs (green); (c) reference pin-GsAs on GaAs substrate (blue). A more pronounced improvement in the photo-response at long wavelengths is observed for the structure containing QDs. This improvement is due to the absorption of photons below the band gap energy of GaAs by InAs QDs. Although the structural properties of the multiple QDs appear rather to be degraded principally as a consequence of the initial surface roughness, the optical and electric properties of pin-GaAs/n+-Si with InAs QDs show that the InAs QDs have been formed and successively contribute to the electron–hole pair creations in the below band gap energy range which increased the photocarrier collections [30,31]. This initial assessment provides evidence of the potential of our proposed yielding structures for the fabrication of future novel, low cost, high performance solar cells. At this time, no contact grid coatings were applied and the electrical contact was basically made with indium-zinc alloys pads on the front surface. In-situ and ex-situ optimization of the solar cell fabrication is in progress, a necessary step to obtain significant values from the active solar cell parameters. 3. Experimental Section The HRXRD experiments were performed with D8 DISCOVER Bruker Axs Diffractometer (BRUKER, Karlsruhe, Germany) with CuKα1 radiation (λ CuKα = 1.5406Å) for ω/2θ values in the range of 32°–35° to investigate the structural properties of GaAs layer grown on nanostructured Si substrate. Figure 6. Sp ctral response of (a) pin-GaAs/ n+-Si with QDs (red); (b) pin-GaAs/n+-Si without QDs (green); (c) reference pin-GsAs on GaAs substrate (blue). 3. ExperimentalSection The HRXRD experiments were performed with D8 DISCOVER Bruker Axs Diffractometer (BRUKER, Karlsruhe, Germany) with CuKα1 radiation (λCuKα = 1.5406Å) forω/2θ values in the range of 32˝–35˝ to investigate the structuralpropertiesofGaAs layergrownonnanostructuredSisubstrate. The PL measurements have been done at 11 K, and the samples mounted in a closed cycle He cryostat, were excited with the 514.5 nm line of an Ar+ laser (Spectra-Physics, Santa Clara, CA, USA) while the spectra were collected using a thermoelectricallycooledInGaAsphotodetector (Oriel,Stratford,CT,USA)usinga conventional lock-in technique. The cross section transmission electron microscopy image was performed using a TEM/STEM Cs-corrected JEOL 2200 FS (JEOL, Peabody, MA, USA) operated at200kV. The spectral respons measurements aim to evaluate the electrical current photogenerated in our samples. The spectral response is measured using a 100 W tu g en halogen lam (Newp rt, Santa Clara, CA, USA), CVI CM110 1/8 m monochromator (Spectral Product, Cvijovica Dolina, CA, USA) and a lock-in amplifier connected to a chopper (at 172 Hz) placed at the outlet of the sourcemonochromator. 4. Conclusions InAs/GaAsQD-basedpinGaAssolarcellsdirectlygrownonsiliconsubstrate havebeendemonstratedfor thefirst timebyusingthenanostructuredsurfaceasa buffer layer. This initial assessment shows the formation of InAs nanostructure, with an emission wavelength of around 1100 nm. The insertion of multiple layer QDs 193