Spectrum Splitting of Solar Radiation for Efficient Conversion via Photovoltaics /

Abstract

Solar power has the raw potential to fulfill a considerable portion of global energy needs, while avoiding most of the negative side effects associated with conventional energy sources. Photovoltaics have many advantages among solar energy conversion technologies, but it has numerous challenges. One of them is the efficiency limit on single junction photovoltaics (Shockley-Queisser limit). An oft studied and used technique to work around this limit is to use multijunction PV cells. However, the commonly used stacked multijunctions are expensive and difficult to manufacture. Spectrum splitting techniques have the potential to minimize these issues and make multijunction photovoltaics more feasible. The objective of this study is to investigate a specific method of spectrum splitting for achieving high efficiency photovoltaic cells. For this purpose, a methodology is devised for the design of a diffractive spectrum splitting system, which is focused on quickly designing a splitting system for any given combination of two laterally arranged PV cells. The design is carried out using physical optics as well as ray tracing and simulated in the optical design software Zemax Optic Studio. A system is designed with a grating and lens combination that manages to split the 350nm to 1100nm band into two bands, 350 to 570 nm for Perovskite and 570 to 1100 nm for Silicon. Along with splitting, geometric concentration ratios of 3.27 and 5.46 are achieved for Silicon and Perovskite respectively. The photocurrent density resulting from this distribution of the spectrum is calculated by using it with experimental EQE data for Silicon and Perovskite and the AM 1.5 spectrum. It is found that the photocurrent from the combination of Si and Perovskite cells with the designed system is ~2.5 times the photocurrent without it.