Browsing by Subject "photovoltaics"

Now showing 1 - 3 of 3

Open Access
Chemically specific dynamic characterization of photovoltaic and photoconductivity effects of nanostructures by X-ray photoelectron spectroscopy
(2010) Ekiz, Okan Öner
X-Ray Photoelectron Spectroscopy is a widely used characterization method for chemical analysis of surfaces. In this thesis, We report characterization of photovoltaic and photoconductivity effects on nanostructured surfaces through light induced changes in the X-ray photoelectron spectra (XPS). The technique combines the chemical specificity of XPS and the power of surface photovoltage spectroscopy (SPV), with the addition of the ability to characterize photoconductivity under both static and dynamic optical excitation. A theoretical model that quantitatively describes the features of the observed spectra is presented. We demonstrate the applicability of the model on a multitude of sample systems, including homo- and heterojunction solar cells, CdS nanoparticles on metallic or semiconducting substrates, and carbon nanotube films on silicon substrates. A-Si/c-Si heterojunction solar cell is fabricated to characterize photovoltage generation in a nanostructured solar cell. Cadmium Sulfide (CdS) nanoparticles were synthesized by a solvothermal route. Both Multi Wall Carbon Nanotube (MWCNT) and Single Wall Carbon Nanotube (SWCNT) films were characterized with different substrates by XPS. Raman Microscopy, EDS, SEM, XRD, SAXS are used to characterize the samples and solar cells.
Open Access
Novel ultraviolet scintillators based on semiconductor quantum dot emitters for significantly enhanced photodetection and photovoltaics
(2007) Mutlugün, Evren
Silicon photonics opens opportunities to realize optoelectronic devices directly on large-scale integrated electronics, leveraging advanced Si fabrication and computation capabilities. However, silicon is constrained in different aspects for use in optoelectronics. Such one limitation is observed in Si based photodetectors, cameras, and solar cells that exhibit very poor responsivity in the ultraviolet (UV) spectral range. Si CMOS photodetectors and CCD cameras cannot be operated in UV, despite the strong demand for UV detection and imaging in security applications. Also, although 95% of the photovoltaics market is dominated by Si based solar cells, silicon is not capable of using UV radiation of the solar spectrum for solar energy conversion, as required especially in space applications. In this thesis for the first time, we demonstrate novel UV scintillators made of semiconductor quantum dot emitters hybridized on Si detectors and cameras to detect and image in UV with significantly improved responsivity and on Si solar cells to generate electrical energy from UV radiation with significantly improved solar conversion efficiency. We present the device conception, design, fabrication, experimental characterization, and theoretical analysis of these UV nanocrystal scintillators. Integrating highly luminescent CdSe/ZnS core-shell nanocrystals, we demonstrate hybrid photodetectors that exhibit two-orders-of-magnitude peak enhancement in their responsivity. We also develop photovoltaic nanocrystal scintillators to enhance open-circuit voltage, short-circuit current, fill factor, and solar conversion efficiency in UV. Hybridizing CdSe/ZnS quantum dots on Si photovoltaic devices, we show that the solar conversion efficiency is doubled under white light illumination (Xe lamp). Such UV scintillator nanocrystals hold great promise to enable photodetection and imaging in UV and extend photovoltaic activity to UV.
Open Access
Semiconductor-less photovoltaic device
(IEEE, 2013) Atar, Fatih B.; Battal, Enes; Aygun, Levent E.; Dağlar, Bihter; Bayındır, Mehmet; Okyay, Ali Kemal
We demonstrate a novel semiconductor-less photovoltaic device and investigate the plasmonic effects on this device structure. The device is made of metal and dielectric layers and the operation is based on hot carrier collection. We present the use of surface plasmons to improve energy conversion efficiency. The field localization provided by surface plasmons confine the incident light in the metal layer, increasing the optical absorption and hot electron generation rate inside the metal layer. The device consists of two tandem MIM (metal-insulator-metal) junctions. Bottom MIM junction acts as a rectifying diode and top MIM junction is used to excite surface plasmons. The device operation principle as well as the topology will be discussed in detail. © 2013 IEEE.