Enhancing Quantum Efficiency of Thin Film Solar Cells via Joint Characterization of Radiation and Recombination

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Thin film solar cells are at the forefront of innovation in photovoltaics technology. However, the efficiency of thin film solar cells is significantly lower than bulk cells, limiting the scale of their application. Light trapping schemes based on structural modifications have been used to improve the efficiency of nano-scale photovoltaic devices. These schemes affect both radiative and electrical characteristics of thin semiconductors in complex ways. These effects are neither accurately modeled nor well known. This research fills this knowledge gap by modeling the combined radiative and electrical effects of light trapping. The proposed models will be diverse, comprehensive and more accurate than the existing literature. By using the improved models, novel architectures can be designed for solar cell devices with enhanced conversion efficiencies and reduced energy payback periods compared to the state-of-the-art technology which is highly valuable to the US economy. Additionally, the work leads to better understanding of the radiative effects of nano-structural modifications which is imperative in nano-scale radiation applications beyond photovoltaics.This project investigates methods to systematically enhance the quantum efficiency of nano-scale thin film solar cells. To this end, fundamentals of light-trapping affected radiation at nano-scale are studied. Analytical models are formulated for explaining radiation in non-homogenous semiconductors along with electrical carrier recombination. The radiative models are based on improved estimations of the local density of optical states in the presence of pseudo-periodic Metallo-dielectric surface and bulk patterns, and accurate estimation of extinction cross-section in plasmonic nano-particles based on improvements of Mie scattering using mathematical shape formulations and data fitting. Overlaying radiative effects from multiple mechanisms are modeled and combined with carrier transport models under realistic material imperfections and physical defects assumptions. The work utilizes the improved models to design structures with broad-band/angle optical absorption beyond the ergodic limits, and quantum efficiencies approaching the limits of bulk cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.