Hybrid tandem photovoltaics
- It is estimated that for photovoltaics to reach grid parity around the planet, they must be made with costs under $0.50 per W and must also achieve power conversion efficiencies above 20% in order to keep installation costs down. Although solar cells exist that have passed this efficiency threshold none is definitely capable of meeting this high standard at such a low cost. I have explored a novel solar cell architecture, a hybrid tandem photovoltaic (HTPV), which I believe is capable of meeting these targets. HTPV is composed of an inexpensive and low temperature processed solar cell, such as an organic or dye sensitized solar cell, that can be printed on top of one of a variety of more traditional inorganic solar cells to form a high efficiency multijunction device. In this dissertation, I first discuss the modeling done to estimate the efficiency potential for HTPV. I explore a variety of design options and assess how each impacts the performance of the hypothetical device. My modeling shows that HTPV has great potential. An organic solar cell may be added on top of a commercial CIGS cell, for example, to improve its efficiency from 15.1% to 21.4%, thereby reducing the cost of the modules by ~15% and the cost of installation by up to 30%. Secondly, I present my experimental progress toward a working hybrid tandem device. I demonstrate a high efficiency semi-transparent organic solar cell, which is the precursor to a hybrid tandem. Arguably the most challenging part of fabricating a high performing semi-transparent cell is depositing a transparent electrode on top of the organic active layer. The requirements for this layer are stringent; it must be conducting enough to collect photogenerated carriers with low resistive losses while being as transparent as possible to unabsorbed light. The semi-transparent organic solar cells use a silver nanowire - ZnO nanoparticle composite top electrode, and have a power conversion efficiency of 5.0%. As importantly, these cells have excellent optical performance, transmitting ~81% of the light below and ~34% of the light above the band gap of the organic absorber. I discuss my approach to designing these devices, which has relied heavily on transfer matrix optical modeling both as a predictive tool to guide my design choices and as a method of characterization. I also present an estimate of the efficiency of an HTPV device based on the semi-transparent solar cells, and discuss the reasons that the current experimental devices have not yet achieved the efficiencies predicted by my modeling. Lastly, I discuss the potential for the commercialization of HTPV technology and what needs to be done to push HTPV to efficiencies above 20% and costs below $0.50 per W.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Beiley, Zachary Michael
|Stanford University, Department of Materials Science and Engineering.
|Statement of responsibility
|Zachary Michael Beiley.
|Submitted to the Department of Materials Science and Engineering.
|Thesis (Ph.D.)--Stanford University, 2013.
- © 2013 by Zachary Michael Beiley
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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