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- All Subjects: energy
- All Subjects: Lithium
- Creators: Holman, Zachary
- Resource Type: Text
This document outlines work completed to this end. Chapter 1 introduces the areas for cost reductions and improvements in efficiency to drive down the cost per watt of solar modules. Next, in Chapter 2, conventional and advanced metallization methods are reviewed, and our proposed solution of dispense printed reactive inks is introduced. Chapter 3 details a proof of concept study for reactive silver ink as front metallization for solar cells. Furthermore, Chapter 3 details characterization of the optical and electrical properties of reactive silver ink metallization, which is important to understanding the origins of problems related to metallization, enabling approaches to minimize power losses in full devices. Chapter 4 describes adhesion and specific contact resistance of reactive ink metallizations on silicon heterojunction solar cells. Chapter 5 compares performance of silicon heterojunction solar cells with front grids formed from reactive ink metallization and conventional, commercially available metallization. Performance and degradation throughout 1000 h of accelerated environmental exposure are described before detailing an isolated corrosion experiment for different silver-based metallizations. Finally, Chapter 6 summarizes the main contributions of this work.
The major goal of this project is to evaluate potential of a new metallization technique –high-precision dispense printing of reactive inks–to become a high efficiency replacement for solar cell metallization through optical and electrical characterization, evaluation of durability and reliability, and commercialization research. Although this work primarily describes the application of reactive silver inks as front-metallization for silicon heterojunction solar cells, the work presented here provides a framework for evaluation of reactive inks as metallization for various solar cell architectures and electronic devices.
Mg0.13Cd0.87Te (1.7 eV), also with high material quality, has been proposed as a current matching cell to Si (1.1 eV) solar cells, which could potentially enable a tandem solar cell with high efficiency and thus lower the electricity cost. The properties of Mg0.13Cd0.87Te/Mg0.5Cd0.5Te DHs and solar cells have been investigated. Carrier lifetime as long as 0.56 μs is observed and a solar cell with 11.2% efficiency and open circuit voltage of 1.176 V is demonstrated.
The CdTe/MgxCd1-xTe DHs could also be potentially applied to luminescence refrigeration, which could be used in vibration-free space applications. Both external luminescence quantum efficiency and excitation-dependent PL measurement show that the best quality samples are almost 100% dominated by radiative recombination, and calculation shows that the internal quantum efficiency can be as high as 99.7% at the optimal injection level (1017 cm-3). External luminescence quantum efficiency of over 98% can be realized for luminescence refrigeration with the proper design of optical structures.
Monocrystalline CdTe/MgCdTe double-heterostructures (DHs) grown on lattice-matched InSb substrates have demonstrated impressively long carrier lifetimes in both unintentionally doped and Indium-doped n-type CdTe samples. The non-radiative recombination inside of, and at the interfaces of the CdTe absorbers in CdTe/MgCdTe DH samples has been significantly reduced due to the use of lattice-matched InSb substrates, and the excellent passivation provided by the MgCdTe barrier layers. The external luminescent quantum efficiency (η_ext) of n-type CdTe/MgCdTe DHs is up to 3.1%, observed from a 1-µm-thick CdTe/MgCdTe DH doped at 1017 cm-3. The 3.1% η_ext corresponds to an internal luminescent quantum efficiency (η_int) of 91%. Such a high η_ext gives an implied Voc, or quasi-Fermi-level splitting, of 1.13 V.
To obtain actual Voc, the quasi-Fermi-level splitting should be extracted to outside the circuit using a hole-selective contact layer. However, CdTe is difficult to be doped p-type, making it challenging to make efficient PN junction CdTe solar cells. With the use of MgCdTe barrier layers, the hole-contact layer can be defective without affecting the voltage. P-type hydrogenated amorphous silicon is an effective hole-selective contact for CdTe solar cells, enabling monocrystalline CdTe/MgCdTe DH solar cells to achieve Voc over 1.1 V, and a maximum active area efficiency of 18.8% (Jsc = 23.3 mA/cm2, Voc = 1.114 V, and FF = 72.3%). The knowledge gained through making the record-efficiency monocrystalline CdTe cell, particularly the n-type doping and the double-heterostructure design, may be transferable to polycrystalline CdTe thin-film cells and improve their competitiveness in the PV industry.
Lithium ion batteries are quintessential components of modern life. They are used to power smart devices — phones, tablets, laptops, and are rapidly becoming major elements in the automotive industry. Demand projections for lithium are skyrocketing with production struggling to keep up pace. This drive is due mostly to the rapid adoption of electric vehicles; sales of electric vehicles in 2020 are more than double what they were only a year prior. With such staggering growth it is important to understand how lithium is sourced and what that means for the environment. Will production even be capable of meeting the demand as more industries make use of this valuable element? How will the environmental impact of lithium affect growth? This thesis attempts to answer these questions as the world looks to a decade of rapid growth for lithium ion batteries.