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Open Access Publications from the University of California

Material Development for Highly Processable Thin Film Solar Cells

  • Author(s): Bob, Brion
  • Advisor(s): Yang, Yang
  • et al.

The ability of a photovoltaic cell to convert incident photons into electrical power is determined by the properties of its constituent materials and on their ability to function in concert with one another. Thin film solar cell materials benefit from the use of thin absorber layers that are relatively tolerant of a variety of structural defects. This allows for absorber layers to be made from polycrystalline films fabricated using raw materials that do not need to be refined to incredible levels of purity, as is generally required for single crystalline solar materials. Each of these traits represents significant logistical advantages during the industrial scale-up of thin film technologies, but they can be severely offset if scarce, expensive, or toxic materials are required during device fabrication. The various studies contained in the following chapters are dedicated to the exploration of next generation material systems that are being developed to resolve material issues that could potentially inhibit the large-scale implementation of existing thin film solar cell technologies.

Silver nanowire networks stand as a potential replacement for transparent conductors made from doped metal oxide films. They exhibit excellent optical and electronic performance, and can be deposited in minutes from benign solutions with little damage to underlying device layers. When combined with an appropriately chosen matrix material to surround and encapsulate the wires, the resulting wire/matrix nanocomposite becomes a highly versatile electrode that can be integrated into a variety of thin film devices. Much of this dissertation is dedicated to the study and analysis of silver nanowire networks and partner materials and their applications in Cu(In,Ga)Se2 (CIGS) and amorphous silicon (a-Si) photovoltaics, starting from material synthesis and ink formulation and ending with device fabrication and characterization. In addition, the last chapter is dedicated to a discussion of heterojunction and space-charge formation in CZTSe solar cells, which is quickly becoming understood as a far more sensitive process than in its various chalcogenide analogues such as CIGS and CdTe. Together this set of materials would pave the way for the arrival of next generation thin film devices that can be fabricated quickly and with minimal reliance on indium, tellurium, or any other elements that would prevent their widespread commercial adoption.

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