Photon recycling reduces the effect of radiative recombination and is an approach to obtain the device performance described by detailed balance theory. The main carrier recombination mechanisms in the GaAs-based solar cells are surface recombination, radiative recombination and non-radiative recombination. GaAs-based solar cells have attracted much interest because of their high conversion efficiencies of ~28% under one sun illumination.
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A designed of a-Si free carrier-selective contact MoOx/Si/GaP solar cells demonstrated 14.1% power conversion efficiency. To achieve high performance of GaP/Si solar cells, different GaP/Si structures were designed, fabricated and compared, including GaP as a hetero-emitter, GaP as a heterojunction on the rear side, inserting passivation membrane layers at the GaP/Si interface, and GaP/wet-oxide functioning as a passivation contact. Two practical approaches including the use of both a SiNx diffusion barrier layer and P-diffused layers, to suppress the Si minority-carrier lifetime degradation during GaP epitaxial growth on Si by MBE were proposed. The mechanisms responsible for lifetime degradation were further investigated, and it was found that external fast diffusors are the origin for the degradation. High quality GaP can be realized on precisely oriented (001) Si substrates by MBE growth, and the investigation of structural defect creation in the GaP/Si epitaxial structures was conducted using high resolution X-ray diffraction (HRXRD) and high resolution transmission electron microscopy (HRTEM). In this dissertation, two different GaP growth methods were compared and analyzed, including migration-enhanced epitaxy (MEE) and traditional molecular beam epitaxy (MBE). Further, it is widely observed that the minority-carrier lifetime of the Si substrates is significantly decreased during epitaxially growth of GaP on Si.
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First, the growth of the polar material (GaP) on the non-polar material (Si) is a challenge in how to suppress the formation of structural defects, such as anti-phase domains (APD). The band offset between Si and GaP suggests that GaP can function as an electron-selective contact, and it has been theoretically shown that GaP/Si integrated solar cells have the potential to overcome the limitations of common a-Si based heterojunction (SHJ) solar cells.ĭespite the promising potential of GaP/Si heterojunction solar cells, there are two main obstacles to realize high performance photovoltaic devices from this structure. Gallium phosphide with small lattice mismatch (~0.4%) to Si enables coherent/pseudomorphic epitaxial growth with little crystalline defect creation. Among the III-V alloys, gallium phosphide (GaP) is a strong candidate, especially for solar cells applications. Progress in Photovoltaics: Research & Applications Wiley It has been a long-standing goal to epitaxially integrate III-V alloys with Si substrates which can enable low-cost microelectronic and optoelectronic systems. Finally, we show that with correct parameters, the one‐dimensional simulation of very thin silicon solar cells can successfully be performed. Additionally, the optical influence of the laser‐fired contacts (LFC) process is experimentally investigated. We apply the optical analysis to samples with different thickness, silicon oxide layer thickness, rear side topography as well as passivation layers (SiO2, SiNx, SiC and stack systems). The free‐carrier‐absorption (FCA) as non‐carrier‐generating absorption channel is analyzed for solar cells with varying thickness. In this paper, we investigate in detail the meaning of this single‐value parameter, its correct determination and the use in one‐dimensional simulations with PC1D. This optical performance is often shown as values for the back side reflectance Rb which describes the rear internal reflection. New passivation layers for the back side of silicon solar cells have to show high performance in terms of electrical passivation as well as high internal reflectivity. Kray, Daniel Hermle, Martin Glunz, Stefan W. Theory and experiments on the back side reflectance of silicon wafer solar cells Theory and experiments on the back side reflectance of silicon wafer solar cells