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Published June 2011 | public
Book Section - Chapter

Direct evidence of Mg-Zn-P alloy formation in Mg/Zn_3P_2 solar cells


Zinc phosphide (Zn_3P_2) is a promising and earth-abundant alternative to traditional materials (e.g. CdTe, CIGS, a-Si) for thin film photovoltaics. The record solar energy conversion efficiency for Zn_3P_2 cells of 6% (M. Bhushan et al., Appl. Phys. Lett., 1980) used a Mg/Zn_3P_2 device geometry that required annealing to reach peak performance. Here we report photovoltaic device results and junction composition profiles as a function of annealing treatment for ITO/Mg/Zn_3P_2 devices. Mild annealing at 100 °C in air dramatically increases V_(oc) values from ~150 mV to 550 mV, exceeding those of the record cell (V_(oc, record) = 490 mV). In devices with thinner Mg films we achieved J_(sc) values reaching 26 mA cm^(-2), significantly greater than those of the record cell (J_(sc, record) = 14.9 mA cm^(-2)). Junction profiling by secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS) both show evidence of MgO and Mg-Zn-P alloy formation at the active photovoltaic junction in annealed ITO/Mg/Zn_3P_2 devices. These results indicate that high efficiency should be realizable by optimization of Mg treatment in Mg/Zn_3P_2 solar cells.

Additional Information

© 2011 IEEE. We acknowledge Yunbin Guan and the Division of Geological and Planetary Sciences at Caltech for assistance collecting SIMS data. This work was supported by the Office of Energy Efficiency and Renewable Energy, US Department of Energy under grant DE-FG36-08GO18006, the Molecular Materials Research Center (MMRC) of the Beckman Institute at the California Institute of Technology, as well as a partnership with the Dow Chemical Company. One of us (GMK) acknowledges support under an NDSEG graduate fellowship.

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October 20, 2023