Sensitivity Analysis of Optical Metrics for Spectral Splitting Photovoltaic Systems: A Case Study

Spectral splitting of sunlight to increase photovoltaic (PV) efficiency beyond the Shockley-Queisser limit has gained interest in recent years. Sensitivity analysis can be a useful tool for system designers to determine how much deviation from ideal conditions can be tolerated for different optical parameters. Understanding the origin of these sensitivities can offer insight into materials and device design. We employ 2-D TCAD simulations to analyze the sensitivity of system performance to two optical parameters: spectral fidelity (the fraction of photons directed to the intended material) and the spatial uniformity of illumination intensity. We analyze a system using crystalline silicon (Si) and cuprous oxide (Cu2O) as absorbers. We find that the spectral fidelity of the light directed to the Si cell has to be greater than 90% for the system to outperform a high-efficiency single-junction Si device. Varying the fidelity of the light directed to the Cu2O cell from 55% to 90% changes system efficiency by less than 10% relative. In some cases, increasing the fidelity of this light reduces system efficiency. We find no significant impact of spatial variation on length scales from 600 μm to 4.8 mm in devices with emitter sheet resistance less than 500 Ω/□.

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