| dc.identifier.uri | http://hdl.handle.net/11401/76633 | |
| dc.description.sponsorship | This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree. | en_US |
| dc.format | Monograph | |
| dc.format.medium | Electronic Resource | en_US |
| dc.language.iso | en_US | |
| dc.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dc.type | Dissertation | |
| dcterms.abstract | A substantial challenge in the development of optoelectronic devices such as photovoltaics and photodetectors is the inherent non-uniformity in semi-crystalline and polycrystalline photoactive materials. The focus of this work is to understand and evaluate the impact of specific non-uniformities in organic and inorganic materials, and present strategies for the development of novel architectures where instead of being detrimental they can be beneficial to device performance. We focus on materials in two regimes: a) materials with small dielectric constants, where the Coulomb interaction between an electron and a hole is strong therefore forming Frenkel excitons, with radii of the same order as the size of the unit cell; b) materials with larger dielectric constants, where electric field screening tends to reduce the Coulomb interaction forming Wannier excitons with radii larger than lattice spacing. In the first regime, we focus on organic electronic materials specifically poly-(3 hexylthiophene), a conjugated semiconducting polymer and electron donor, and [6,6]-phenyl-C-61-butyric acid methylester, an electron accepting fullerene derivative. We measure the donor-acceptor volume fraction and the inter-chain disorder in thin films as the film thickness approaches the confinement limit (less than 20nm), using variable angle spectroscopic ellipsometry and near-edge X-ray absorption fine structure spectroscopy. Furthermore, we also investigate the effect of confinement on the coherence length and the crystalline microstructure of the polymer component using grazing incidence wide angle X-ray scattering. As the film thickness is decreased to the confinement regime, the films became less phase segregated and the polymer component formed less disordered (more aligned along the surface normal) and smaller crystallites. In the second regime of materials with larger dielectric constants, we focus on understanding the recombination mechanism in polycrystalline Cu(In_{1-x}Ga_x)Se_2 due to material compositional inhomogeneity. We measure the charge transport behavior as a function of temperature of few-grain regions using lithographically defined electrical contacts. We correlate these measurements with energy dispersive X-ray spectroscopy and aberration corrected transmission electron microscopy with selected area electron diffraction. We find that local regions with higher fraction of copper-rich grains show enhanced interfacial recombination whereas regions with a higher fraction of copper-poor grains show standard bulk recombination behavior. Finally, we present novel architectures where material non-uniformities localized at surfaces are used beneficially: a) we demonstrate strong (2.11x10^{13} e/cm^2), robust, and spontaneous graphene n-doping on polycrystalline Cu(In_{1-x}Ga_x)Se_2 due to surface-transfer doping from Na atoms that diffuse to the surface from the soda-lime-glass substrate. b) we demonstrate broadband tunable anti-reflection using densely packed silicon nanotextures, comprising a surface layer whose optical properties differ substantially from those of the bulk, providing the key to improved performance. | |
| dcterms.available | 2017-09-20T16:50:50Z | |
| dcterms.contributor | Weinacht, Thomas C. Allen, Philip B. Ocko, Benjamin M. Venkatesh, T. | en_US |
| dcterms.contributor | Eisaman, Matthew D. | en_US |
| dcterms.creator | Ashraf, Ahsan | |
| dcterms.dateAccepted | 2017-09-20T16:50:50Z | |
| dcterms.dateSubmitted | 2017-09-20T16:50:50Z | |
| dcterms.description | Department of Physics | en_US |
| dcterms.extent | 156 pg. | en_US |
| dcterms.format | Application/PDF | en_US |
| dcterms.format | Monograph | |
| dcterms.identifier | http://hdl.handle.net/11401/76633 | |
| dcterms.issued | 2016-12-01 | |
| dcterms.language | en_US | |
| dcterms.provenance | Made available in DSpace on 2017-09-20T16:50:50Z (GMT). No. of bitstreams: 1
Ashraf_grad.sunysb_0771E_12860.pdf: 26113728 bytes, checksum: ab3a93062d31bd957e7a773284e06a29 (MD5)
Previous issue date: 42370 | en |
| dcterms.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dcterms.subject | Physics -- Condensed matter physics -- Nanoscience | |
| dcterms.subject | ellipsometry, inhomogeneity, nanoscale, organic photovoltaics, photovoltaics, surface science | |
| dcterms.title | Nanoscale Spatial Inhomogeneity in Photovoltaic Devices | |
| dcterms.type | Dissertation | |
