Electron-Hole Separation in Ferroelectric Oxides for Efficient Photovoltaic Responses

TL;DR

This paper uses first-principles calculations to understand electron-hole separation in ferroelectric oxides, identifying key materials and strategies to improve photovoltaic efficiency beyond current limitations.

Contribution

It reveals that electron-hole separation in BFCO and related oxides is crucial for high photovoltaic performance and proposes new materials with enhanced charge separation capabilities.

Findings

Electron-hole pairs are spatially separated in BFCO, especially in disordered phases.

Disordered BFCO phases show exceptional photovoltaic responses.

Nine novel Bi-based double-perovskite oxides are proposed for improved FPVs.

Abstract

Despite their potential to exceed the theoretical Shockley-Queisser limit, ferroelectric photovoltaics (FPVs) have performed inefficiently due to their extremely low photocurrents. Incorporating Bi2FeCrO6 (BFCO) as the light absorber in FPVs has recently led to impressively high and record photocurrents [Nechache et al. Nature Photon. 2015, 9, 61], reviving the FPV field. However, our understanding of this remarkable phenomenon is far from satisfactory. Here, we use first-principles calculations to determine that such excellent performance mainly lies in the efficient separation of electron-hole (e-h) pairs. We show that photoexcited electrons and holes in BFCO are spatially separated on the Fe and Cr sites, respectively. This separation is much more pronounced in disordered BFCO phases, which show exceptional PV responses. We further set out to design a strategy for next-generation FPVs, not limited to BFCO, by exploring 44 additional Bi-based double-perovskite oxides. We suggest 9 novel active-layer materials that can offer strong e-h separations and a desired band gap energy for application in FPVs. Our work indicates that charge separation is the most important issue to be addressed for FPVs to compete with conventional devices.