Influence of realistic operation conditions on silicon solar cells and energy yield

Abstract: This thesis discusses studies performed by the author at the Fraunhofer Institute for Solar Energy Systems, ISE. The main goal of this thesis was the analysis temperature sensitivities of silicon solar cells based on experimental data and simulation studies. The main achievements are:

•A literature review of studies of temperature-dependent solar cell characteristics is given. The review provides a basis of fundamental physics behind temperature sensitivity of solar cells and helps to understand the underlying physics of local temperature dependencies in mono- as well as multicrystalline silicon.
•Measurement approaches for spatially-resolved temperature-dependent characterization of silicon wafers and solar cells were developed. For silicon wafers the method is based on lifetime-calibrated photoluminescence imaging, measurements are completed between 15°C to up to 70°C, which represent realistic temperatures of operation. Silicon solar cells are characterized by photoluminescence imaging, lock-in thermography as well as light-beam-induced-current measurements in a temperature dependent manner to assess local temperature sensitivity of cell performance.
•The temperature dependence of three different regions of silicon solar cells have been investigated: (i) the bulk, (ii) surfaces and (iii) diffused regions.
•(i) A broad study of the temperature-dependent local open-circuit voltage VOC based on bulk lifetime measurements was conducted. Very different materials ranging from standard industrial multicrystalline silicon to high quality float zone silicon were characterized for their temperature sensitivity of VOC by lifetime-calibrated photoluminescence imaging. It it shown that for some multicrystalline samples, a deviation to the analytical temperature sensitivity is obvious in areas with high dislocation density, the same does not occur in high quality sample areas. From this extensive study and its broad variety of data it is concluded that uncontaminated crystal defects such as sliplines or dislocation clusters do not influence a cell’s temperature sensitivity outside literature expectation. However, possibly contamination with metals which induce a SRH defect level of Et-E¬v or Ec-E¬t of 0.2 eV to 0.3 eV with low symmetry factor may lead to decreased temperature sensitivity due to a strong increase in effective lifetime eff with increasing temperature.
•(ii) The temperature-dependent surface recombination velocity was investigated via a thickness variation of float zone samples with surface passivation of aluminum-oxide. The experimental investigation showed that surface recombination is highly dependent on temperature and its temperature sensitivity might be influenced by excess charge carrier density n.
•(iii) To get insights into the physics behind temperature sensitivity of silicon solar cells the temperature dependence of recombination in diffused layers, such as the emitter, is studied by an analysis of the dark saturation current J0. Via a variation of emitter dopant and sheet resistivity it is shown that J0/ni2, which was commonly assumed to be independent of temperature, is increasing significantly with temperature and neglecting its temperature sensitivity can cause errors of up to 30 % for studied samples in this thesis. This behaviour seems to be independent of injection and sheet resistivity.
•A sensitivity analysis was conducted to demonstrate how new findings about temperature sensitivity of silicon solar cells influence numerical simulations of silicon solar cell devices. It is shown that the implementation of further temperature dependencies of input parameters into device simulation leads to deviations to temperature coefficients from common simulations of several percent. Wrong assumptions of temperature-dependent bulk lifetime, emitter recombination and contact resistivity affect the simulated efficiency at temperatures deviating from STC. However, this effect is too weak to affect predicted energy yield significantly.
•The yearly energy yield for silicon solar modules is predicted via measurements at wafer level before metallization in spatial resolution. In most multicrystalline silicon solar cells highly contaminated dislocation clusters are characterized by decreased temperature sensitivity, which leads to higher energy yield when it is normalized to its power at STC. Hence, improved temperature sensitivity leads to a decreasing gap between bad and good areas in mutlicrystalline silicon at higher temperatures. However, this improved temperature sensitivity cannot compensate the overall reduced material quality and the overall yearly energy yield is still lower in areas of minor material quality compared to high quality areas.
•The conducted studies give valuable insights into temperature sensitivities of silicon solar cells and their device layers as well as bulk material, and furthermore, how they influence the silicon solar modules’ energy yield. The shown approaches shall enable an optimization of silicon solar cells for realistic operation temperatures. Analyzing the influence of various processing steps on a solar cell’s temperature sensitivity as well as identifying local inhomogeneity are key parameters to improve temperature coefficients of silicon solar cells in order to increase the yearly energy yield of solar modules for the intended location of operation

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2020

Klassifikation und Themen

• Klassifikation: Elektrotechnik, Elektronik
• Schlagwort: Silicon ; Force and energy ; Silicon solar cells ; Silicium ; Solarzelle ; Temperaturabhängigkeit

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2021
• Urheber: Eberle, Rebekka
• Beteiligte Personen und Organisationen: Glunz, Stefan ; Reindl, Leonhard M. ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/175563
• URN: urn:nbn:de:bsz:25-freidok-1755630
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:54 MEZ