Enhancing the performance of low concentrating photovoltaics via spectral conversion
Date: 9 March 2020
University of Exeter
The spectral mismatch between the incoming solar spectrum and photovoltaic cells is a fundamental factor which curtails their efficiencies. Through luminescent processes, known as spectral conversion, the wavelengths of the incident sunlight may be changed to better match the optimal values for charge carrier generation by the solar ...
The spectral mismatch between the incoming solar spectrum and photovoltaic cells is a fundamental factor which curtails their efficiencies. Through luminescent processes, known as spectral conversion, the wavelengths of the incident sunlight may be changed to better match the optimal values for charge carrier generation by the solar cell. There are three means by which this can occur: upconversion, downconversion and luminescent downshifting, whereby two low energy photons can combine into one of a higher energy, one high energy photon can split its energy into two lower energy ones and a single high energy photon can reduce its energy, respectively. Collectively, these processes have attracted interest as an area of research for their application to solar cells as a method to enhance PV device performance, an important technological challenge to aid in the transition to a decarbonised economy. In this thesis, particles with spectral conversion properties are incorporated into two kinds of novel solar PV devices of relevance to the emerging and building integrated photovoltaic technology sectors, 3D static SEH concentrator photovoltaic modules with potential for building integration and high stability dye sensitized solar cells. Following an introduction to the topic, concisely discussing the underlying mechanisms of each spectral conversion process, and conducting a literature review which catalogues the evolution of state-of-the-art results from the field, experiments are designed to test two candidate spectral conversion materials (Sr4Al14O25: Eu2+, Dy3+ and NaYF4: Er3+, Yb3+) on silicon PV and dye sensitized solar cells, both with and without SEH concentrators. Under an A+A+A+ solar simulator at 1000 W/m2, the power conversion efficiency of silicon PV devices improved up to 11.1% relative to controls through the addition of these materials. At lower irradiances and compared to cells without concentrators, the relative efficiency gains were more pronounced and external quantum efficiency (EQE) measurements suggested spectral conversion was potentially responsible for these enhancements. For a large scale BICPV system, a simple analysis showed cost per watt could fall by up to 8.1% and power output increase from 19.3 to 21.4 W/m2 through this approach. For the dye sensitized solar cells a 53.4% efficiency enhancement (relative to un-doped controls) was achieved with a potential cost reduction of 39.6%. Finally, simple optical models (including one developed in-house) and a statistical analysis are used to justify the findings and develop understanding of the physical processes behind the results, while conclusions are drawn with regards to the future outlook of this approach and its impact on the drive towards lower cost sources of clean electricity.
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