EN08.04.11 : A Theoretical Study of GaNP for Low-Cost Tandem Solar Cells

5:00 PM–7:00 PM Apr 3, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E

Yongjie Zou1 Christiana Honsberg1 Stephen Goodnick1

1, Arizona State University, Tempe, Arizona, United States

The highest confirmed efficiency of single-junction solar cells under standard conditions (1-sun AM1.5G spectrum at 25 oC) has remained at 28.8 % for the past 5 years [1, 2]. Although improvements towards reaching the Shockley-Queisser limit (33.5 %) [3, 4] are possible with a single-junction structure, tandem/multi-junction solar cells have demonstrated a pathway to achieving higher efficiencies, e. g., the current 1-sun solar conversion efficiency record, 38.8 % was made by Spectrolab with a 5-junction bonded cell [5], and under concentrated illumination, 46.0 % was demonstrated by a 4-junction bonded cell [6]. However, the cell cost is a key factor for deployment to impact real-world energy production. Si-based tandems are good candidates for low-cost high-efficiency solar cells. They have achieved 31–36 % by mechanical stacking or wafer bonding techniques [2]. A monolithic approach is preferred in terms of cost and manufacturability, since it only requires a single substrate, and fewer growth and processing steps.

Dilute nitride GaNP can be grown lattice-matched to Si, and is a candidate absorber for making monolithic high-efficiency solar cells. We are theoretically and experimentally investigating the properties of GaNP relevant to photovoltaics. Here we report on the theoretical aspects of GaNP/Si tandems using a multi-scale approach starting with the electronic structure and phonon dispersion of GaNP using semi-empirical tight binding calculations. They are then fed into a Monte Carlo simulator to calculate the transport properties. The optical absorption is calculated from the electronic structure, which is poorly understood for the dilute nitrides. These calculated properties will later be input into a commercial device package (Silvaco ATLAS) to simulate the performance of the tandem structures.

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[6] Press Release, Fraunhofer ISE, Dec. 2014 (