abstract: Solar photovoltaic (PV) industry is tipped to be one of the front-runners in the renewable industry. Typically, PV module manufacturers provide a linear or step warranty of 80% of original power over 25 years. This power loss during the field exposure is primarily attributed to the development of performance affecting defects in the PV modules. As many as 86 different defects can occur in a PV module. One of the major defects that can cause significant power loss is the interconnect metallization system (IMS) degradation which is the focus of this thesis. The IMS is composed of cell-interconnect (cell-ribbon interconnect) and string-interconnect (ribbon-ribbon interconnect). The cell interconnect is in turn composed of silver metallization (fingers and busbars) and solder bonds between silver busbar and copper ribbon. Weak solder bonding between copper ribbon and busbar of a cell results in increase of series resistance that in turn affects the fill factor causing a power drop. In this thesis work, the results obtained from various non-destructive and destructive experiments performed on modules exposed in three different climates (Arizona - Hot and Dry, Mexico - Warm and Humid, and California - Temperate) are presented. These experiments include light I-V measurements, dark I-V measurements, infrared imaging, extraction of test samples from the modules, peel strength measurements and four-point resistance measurements. The extraction of test samples was performed using a mechanical method and a chemical method. The merits and demerits of these two methods are presented. A drop of 10.33% in fill factor was observed for a 0.05Ω increase in the series resistance of the modules investigated in this work. Different combinations in a cell that can cause series resistance increase were considered and their effect on fill factor were observed using four-point probe experiments. Peel test experiments were conducted to correlate the effect of series resistance on the ribbon peel strength. Finally, climate specific thermal modelling was performed for 4 different sites over 20 years in order to calculate the accumulated thermal fatigue and also to evaluate its correlation, if any, with the increase of series resistance. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

abstract: The popularity of solar photovoltaic (PV) energy is growing across the globe with more than 500 GW installed in 2018 with a capacity of 640 GW in 2019. Improved PV module reliability minimizes the levelized cost of energy. Studying and accelerating encapsulant browning and solder bond degradation—two of the most commonly observed degradation modes in the field—in a lab requires replicating the stress conditions that induce the same field degradation modes in a controlled accelerated environment to reduce testing time. Accelerated testing is vital in learning about the reliability of solar PV modules. The unique streamlined approach taken saves time and resources with a statistically significant number of samples being tested in one chamber under multiple experimental stress conditions that closely mirror field conditions that induce encapsulant browning and solder bond degradation. With short circuit current (Isc) and series resistance (Rs) degradation data sets at multiple temperatures, the activation energies (Ea) for encapsulant browning and solder bond degradation was calculated. Regular degradation was replaced by the wear-out stages of encapsulant browning and solder bond degradation by subjecting two types of field-aged modules to further accelerated testing. For browning, the Ea calculated through the Arrhenius model was 0.37 ± 0.17 eV and 0.71 ± 0.07 eV. For solder bond degradation, the Arrhenius model was used to calculate an Ea of 0.12 ± 0.05 eV for solder with 2wt% Ag and 0.35 ± 0.04 eV for Sn60Pb40 solder. To study the effect of types of encapsulant, backsheet, and solder on encapsulant browning and solder bond degradation, 9-cut-cell samples maximizing available data points while minimizing resources underwent accelerated tests described for modules. A ring-like browning feature was observed in samples with UV pass EVA above and UV cut EVA below the cells. The backsheet permeability influences the extent of oxygen photo-bleaching. In samples with solder bond degradation, increased bright spots and cell darkening resulted in increased Rs. Combining image processing with fluorescence imaging and electroluminescence imaging would yield great insight into the two degradation modes. / Dissertation/Thesis / Doctoral Dissertation Systems Engineering 2020

Currently, there are two major driving forces for considering alternative materials to lead- based products, specifically interconnections, in electronics applications, including the impending legislation or regulations which may tax, restrict, or eliminate the use of lead and the trend toward advanced interconnection technology, which may challenge the limits of present soldering technology. The reliability of solder joints is a concern because fracture failures in solder joints accounts for 70% of failures in electronic components. Lead-free solders are being investigated as replacements for lead solders currently used in electronics. Thermo-mechanical properties describe the stresses accumulated due to thermal fatigue as a result of CTE mismatch within the system. By understanding the failure mechanisms related to lead-free solders, the application of lead- free solders could be more strategically designed for specific applications. The objective of this thesis is to observe microstructural change in large-area solder joints caused by thermal cycling and relate these changes to reliability issues in large-area lead and lead-free solder constructed semiconductor power devices. This study focused on the microstructural changes within the solder alloy of a large-area solder joint under thermal cycling conditions. Two major primary observations were made from this research, they are: 1) due to a combination of testing conditions and material properties, the lead-free solders, Sn/3.5Ag and Sn/Ag/0.7Cu, sustained the most severe damage as compared to Sn/37Pb, and 2) due to elevated stresses at the solder/substrate interface in a simulated power semiconductor device sample damage was found to be most severe. / Master of Science

<div>The manufacturing cost of solar cells along with their efficiency and reliability define the levelized cost of electricity (LCOE). One needs to reduce LCOE to make solar cells cost competitive compared to other sources of electricity. After a sustained decrease since 2001 the manufacturing cost of the dominant photovoltaic technology based on c-Si solar cells has recently reached a plateau. Further reduction in LCOE is only possible by increasing the efficiency and/or reliability of c-Si cells. Among alternate technologies, organic photovoltaics (OPV) has reduced manufacturing cost, but they do not offer any LCOE gain because their lifetime and efficiency are significantly lower than c-Si. Recently, perovskite solar cells have showed promising results in terms of both cost and efficiency, but their reliability/stability is still a concern and the physical origin of the efficiency gain is not fully understood.</div><div><br></div>In this work, we have collaborated with scientists industry and academia to explain the origin of the increased cell efficiency of bulk solution-processed perovskite cells. We also explored the possibility of enhancing the efficiency of the c-Si and perovskite cells by using them in a tandem configuration. To improve the intrinsic reliability, we have investigated 2D-perovskite cells with slightly lower efficiency but longer lifetime. We interpreted the behavior of the 2D-perovskite cells using randomly stacked quantum wells in the absorber region. We studied the reliability issues of c-Si modules and correlated series resistance of the modules directly to the solder bond failure. We also found out that finger thinning of the contacts at cell level manifests as a fake shunt resistance but is distinguishable from real shunt resistance by exploring the reverse bias or efficiency vs. irradiance. Then we proposed a physics-based model to predict the energy yield and lifetime of a module that suffers from solder bond failure using real field data by considering the statistical nature of the failure at module level. This model is part of a more comprehensive model that can predict the lifetime of a module that suffers from more degradation mechanisms such as yellowing, potential induced degradation, corrosion, soiling, delamination, etc. simultaneously. This method is called forward modeling since we start from environmental data and initial information of the module, and then predict the lifetime and time-dependent energy yield of a solar cell technology. As the future work, we will use our experience in forward modeling to deconvolve the reliability issues of a module that is fielded since each mechanism has a different electrical signature. Then by calibrating the forward model, we can predict the remaining lifetime of the fielded module. This work opens new pathways to achieve 2030 Sunshot goals of LCOE below 3c/kWh by predicting the lifetime that the product can be guaranteed, helping financial institutions regarding the risk of their investment, or national laboratories to redefine the qualification and reliability protocols.<br>