Zagozdzon-Wosik, WandaFreundlich, Alex2018-03-132018-03-13December 22017-12December 2http://hdl.handle.net/10657/2961We have investigated the integration of high efficiency solar cells with ‎crystallographically compatible large grain Ge thin films (fabricated on glass) for cost ‎reduction purposes. We have combined defect tolerant III-V dilute nitride (quantum ‎engineered) solar cells and tunnel diode technologies with low cost poly-Ge substrates ‎‎(developed by Al-Induced Crystallization method). Hence, it was required to allocate our ‎research into three complementary paths, the fabrication of defect tolerant tunnel diodes, ‎implementation of defect tolerant high efficiency quantum structured solar cells and ‎development of low-cost Ge substrates. ‎ First, we theoretically and experimentally evaluated the impact of moderate to ‎large ‎dislocation densities on the performance of GaAs tunnel ‎diodes. We have shown for ‎excessive dislocation ‎densities (ND>1×109 cm-2) I-V characteristics ‎undergo a severe ‎degradation. However, for devices with moderate ‎dislocations (about 2×108cm-2), above ‎what has been perceived as acceptable for PV applications, there is even ‎an improvement ‎in term of peak current densities. ‎ Next, we studied ultra-thin defect tolerant solar cells compatible with highly defective ‎low-cost substrates. A 1eV quantum engineered design was investigated for elevated ‎absorption capability to compensate device thickness reduction. Dilute nitride III-V ‎materials were used for their ideal bandgap in 4-junction solar cells (lattice matched with ‎Ge), high absorption coefficient and mere valence band offset with GaAs (as an ideal ‎case for quantum engineering). A resonantly coupled multi-quantum well and ‎supperlattice system were theoretically and experimentally studied for the validation of a ‎thermo-tunneling concept. The results suggest a world record Voc beyond the radiative ‎limit (0.4 eV below bandgap). ‎ In the last step, we have empirically investigated a low temperature ‎‎(<400C) ‎Al ‎induced ‎crystallization of amorphous Ge on glass. We were initially able to achieve ‎polycrystalline Ge, mainly oriented towards [111] direction, with grain sizes as large as ‎‎200µm. Further, we studied experimental parameters favoring Ge crystallization towards ‎‎[110] or [100] crystals direction, suitable for solar cells application. The AlOx layer, ‎between Al and Ge layer, have been found a critical parameter facilitating Ge ‎crystallization. The thickness of Al layer has been known as determining parameter in ‎selecting [110] cubic crystals orientation or [100] rhombohedral Ge structure.‎application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Solar cellsIII-VDilute nitrideQuantum wellsGeAl Induced CrystallizationThin filmsTunnel Diode2018-03-13Thesisborn digital