In this Letter, we report the alloying of the high-band-gap photovoltaic elemental absorber selenium with the isomorphic low-band-gap semiconductor tellurium to tune the band gap energy of Se1-xTex to the optimal value for photovoltaic absorber. Photovoltaic devices based on crystalline Se1-xTex alloys are promising candidates for extremely cheap and highly scalable solar cells, offering simple low-temperature fabrication and intrinsic stability. We explore the electro-optical properties of Se1-xTex alloys and show that the tellurium red shifts the band gap in a nonlinear manner, faster than expected, due to significantly nonlinear change of the conduction band energy, allowing them to easily reach the desired band gap of 1.2-1.4 eV. On the basis of these results, we rationally design and demonstrate the fabrication of simple Se1-xTex photovoltaic devices, showing significantly improved current density in comparison to pure selenium. Furthermore, we identify and analyze the main factors limiting the device efficiency and suggest a few approaches for future improvements of such photovoltaic devices.
Bibliographical noteFunding Information:
This work was supported in part by the LEAP Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences under Award DE-SC0001059. PYSA measurements were carried out with equipment acquired by ONR Grant N00014-18-1-2102. This work made use of the EPIC facility of Northwestern University’s NUANCE Center, which received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. I.H. acknowledges postdoctoral fellowship support from the Israeli Ministry of Energy, under the program - training of academic personnel in energy-related fields at leading international institutions.
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