Unleashing the Potential of Strain-Engineered Ferroelectric Oxynitrides for Optimal Photovoltaic Performance

Abstract

Ferroelectric photovoltaics have recently captured attention as promising contenders to conventional solar cells, attributed to their capacity to overcome the Shockley–Queisser limit and deliver above-band-gap open-circuit voltage. However, their current power conversion efficiency is suboptimal due to factors such as the energy mismatch between their band gaps and the solar spectrum and reduced polarization upon band gap engineering. In this study, we delve into the properties of the recently predicted new class of materials, polar oxynitrides, under epitaxial strain, which potentially holds the key to enhanced photovoltaic performance. Using first-principles calculations, we find that these materials simultaneously possess an optimal band gap and substantial polarization. Some notable compounds include YGeO2N and LaGeO2N, exhibiting a unique combination of high spontaneous polarization (e.g., ∼160 μC/cm2 for YGeO2N) and tunable band gap values ranging from 0.9 to 3 eV. Our research highlights the potential of strain engineering as a practical strategy for modulating the properties of these oxynitride materials, revealing a spectrum of promising properties across a wide range of tensile strains. These findings not only pave the way for experimental research but also suggest that the future of photovoltaic technology could be shaped by the intricate details of the polar oxynitrides.

Reaching the Potential of Ferroelectric Photovoltaics

“…For example, when BaTiO 3 is doped with Nb and Mn, the E g decreases from 3.1 to 1.66 eV while retaining polarization ( P s = 15 μC/cm 2 ) . Epitaxially induced strain engineering is another route to decrease the bandgap of materials, which has been demonstrated computationally in ferroelectric oxynitrides showing a strain dependent reduction from ∼3 to ∼1.5 eV …”