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%0 Thesis
%A Richter, Alexei
%T Nanocrystalline silicon oxide in silicon heterojunction solar cells
%V 416
%I RWTH Aachen University
%V Dissertation
%C Jülich
%M RWTH-2018-223448
%@ 978-3-95806-310-5
%B Schriften des Forschungszentrums Jülich: Reihe Energie & Umwelt / Energy & Environment
%P 1 Online-Ressource (166 Seiten) : Illustrationen
%D 2018
%Z Druckausgabe: 2018. - Onlineausgabe: 2018. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University
%Z Dissertation, RWTH Aachen University, 2018
%X In the recent decade world record solar energy conversion efficiencies have been achieved by the silicon heterojunction (SHJ) solar cell technology. However, the parasitic absorption within the doped amorphous silicon (a-Si:H) layers still causes a significant reduction in the short circuit current density of a SHJ solar cell. In contrast, thin films of nanocrystalline silicon oxide (nc-SiOx:H) are significantly more transparent. Therefore, the aim of this thesis was to develop doped nc-SiOx:H films at an increased deposition frequency to improve the optoelectronic trade-off of the films and apply these layers in SHJ solar cells to achieve a low parasitic absorption and, thereby, an enhanced short circuit current density. In this work films of nc-SiOx:H were developed at 81.4 MHz using plasma enhanced chemical vapor deposition. By exploiting the increased atomic H density at 81.4 MHz, an improved phase separation was achieved in comparison to films deposited at 13.56 MHz within the same deposition system. Within these variations four distinct regions of nc-SiOx:H deposition were identified according to their microstructure and their properties. In particular these are: a region of amorphous growth (“fully amorphous region”), a region with low amounts of the nc-Si phase and the a-SiOx:H phase (“onset of nc-Si formation”), nc-SiOx:H films of high nc-Si and a-SiOx:H phase contents (“O and nc-Si enrichment”), and a region with a preferential incorporation of a-SiOx:H against nc-Si (“nc-Si deterioration”). Particularly, films deposited at the transition between the “O and nc-Si enrichment” and the “nc-Si deterioration” region exhibited a high optoelectronic performance. A detailed investigation of the microstructure via atom probe tomography revealed the intricate three-dimensional structure of the nc-Si network and indicated a nearly homogeneous distribution of the dopant atoms across all phases in contrast to thermally produced nc-Si in SiO2.After the material development, the nc-SiOx:H layers were applied in SHJ solar cells. Starting with planar substrates passivated by intrinsic a-SiOx:H layers, n-type nc-SiOx:H front-emitter layers led to an increase in the short circuit current density of the solar cells with an increasing a-SiOx:H content in the nc-SiOx:H layers. At the same time, highly transparent nc-SiOx:H layers severely limited the fill factor of the solar cells. These investigations were accompanied by optical simulations using OPAL 2. Additionally, a significant enhancement of the open circuit voltage was achieved by substituting the intrinsic a-SiOx:H by intrinsic a-Si:H due to the superior surface passivation of c-Si by the annealed a-Si:H layers. Furthermore, nano-imprint lithography was employed to produce Si random pyramid textured SiO2-like anti-reflection coatings on planar SHJ solar cells, which enhanced the light incoupling and resulted in an increase of the short circuit current density. The combination of an increased light incoupling and increased light trapping was achieved by Si random pyramid textured Si substrates. Here, the surface passivation of the absorber by intrinsic a-Si:H was confirmed to be comparable to the planar absorbers by considering the effect of the increased surface area and the absorber thickness. In total, a gradual enhancement of the solar energy conversion efficiency from 19 to 21.4
%F PUB:(DE-HGF)3 ; PUB:(DE-HGF)11
%9 BookDissertation / PhD Thesis
%R 10.18154/RWTH-2018-223448
%U https://publications.rwth-aachen.de/record/722212