β-CuGaO₂ as a Strong Candidate Material for Efficient Ferroelectric Photovoltaics

Abstract

We propose a recently discovered material, namely, β-CuGaO2 [T. Omata et al., J. Am. Chem. Soc. 2014, 136, 3378] as a strong candidate material for efficient ferroelectric photovoltaics (FPVs). According to first-principles predictions exploiting hybrid density functional, β-CuGaO2 is ferroelectric with a remarkably large remanent polarization of 83.80 μC/cm2, even exceeding that of the prototypic FPV material, BiFeO3. Quantitative theoretical analysis further indicates the asymmetric Ga 3d z 2 –O 2p z hybridization as the origin of the Pna21 ferroelectricity. In addition to the large displacive polarization, unusually small band gap (1.47 eV) and resultantly strong optical absorptions additionally differentiate β-CuGaO2 from conventional ferroelectrics; this material is expected to overcome critical limitations of currently available FPVs.

Towards photoferroic materials by design: recent progress and perspectives

“…Their large band gap, which is the reason why they can exhibit large photovoltages, is also the cause of their poor power conversion efficiency, since only a small fraction of the solar spectrum is adsorbed and the photocurrent under visible light is small (∼nA cm -2 ) [30]. A good photoferroic material for visible light absorption should enable the ideal combination of an optical gap in the range of 1-2 eV, high electric polarization, suitable e-h mobility, and good stability [31]. Since 2009, BiFeO 3 (BFO)-based materials have been among the most commonly studied photoferroics [32].…”

“…[27] A good photoferroic material for visible light absorption should enable the ideal combination of an optical gap in the range of 1 − 2 eV, high electric polarization, suitable electron-hole mobility, and good stability. [28] Since 2009, BiFeO 3 (BFO)-based materials are among the most commonly studied photoferroics. [29] BFO has a a band gap of around 2.2 eV, but for optimal photoferroic properties it is desirable to find materials with smaller band gaps.…”

Polarization‐Modulated Photovoltaic Effect at the Morphotropic Phase Boundary in Ferroelectric Ceramics

“…For example, the wide bandgap (typically >3.2 eV) of ferroelectric oxides must be reduced to enhance the absorption of solar spectrum, however the robust and switchable FE polarization of those systems is also believed to be critical in promoting the BPVE. [ 14–20 ] Recently, by engineering the polar order in La‐substituted BiFeO 3 epitaxial thin films, large ferroelectric PV enhancement has been reported. [ 21 ] The substitution of La on the A‐site increases the rotational degree of freedom of the polarization and induces competing polar instabilities allowing formation of a compositional phase boundary between the ferroelectric and non‐polar paraelectric phase.…”

Electron−hole separation in ferroelectric oxides for efficient photovoltaic responses

“…However, ferroelectric photovoltaics (FPVs) suffer from extremely low photocurrents (on the order of microamperes per square centimeter under 1 sun illumination), which has mainly been attributed to the wide band gap energy (>2.5 eV) of the active-layer materials [e.g., BiFeO 3 (BFO) and Pb(Zr x Ti 1-x )O 3 (PZT)] ( 10 , 11 ). Tremendous efforts have been made to overcome this challenge, utilizing techniques such as band gap tuning ( 5 , 12 – 14 ), domain structure manipulation ( 2 , 15 ), and multijunction stacking ( 16 , 17 ). Unfortunately, the power conversion efficiencies (PCEs) of FPVs have, until recently, remained too low (≪1%) to be utilized in practical PV applications ( 6 ).…”