Above-bandgap voltages from ferroelectric photovoltaic devices

Abstract

In conventional solid-state photovoltaics, electron-hole pairs are created by light absorption in a semiconductor and separated by the electric field spaning a micrometre-thick depletion region. The maximum voltage these devices can produce is equal to the semiconductor electronic bandgap. Here, we report the discovery of a fundamentally different mechanism for photovoltaic charge separation, which operates over a distance of 1-2 nm and produces voltages that are significantly higher than the bandgap. The separation happens at previously unobserved nanoscale steps of the electrostatic potential that naturally occur at ferroelectric domain walls in the complex oxide BiFeO(3). Electric-field control over domain structure allows the photovoltaic effect to be reversed in polarity or turned off. This new degree of control, and the high voltages produced, may find application in optoelectronic devices.

Polarization-Induced Photovoltaic Effects in Nd-Doped BiFeO3Ferroelectric Thin Films

“…3 and 4 indicate that the present BFO and BNF cells have the polarization-induced photovoltaic effect. 19,21) Generally, the photovoltaic cells with ferroelectrics have two components, the switchable and unswitchable components, which originate from a polarization-induced field and a stable built-in field such as the Schottky barrier, respectively, as follows: 29)…”

“…14,[17][18] Recently, polarization-induced photovoltaic properties in BFO films have been reported. [19][20][21] The photovoltaic properties are completely different from those of conventional pn and Schottky junctions originating from the built-in-field induced by space charge in depletion layers. Among the ferroelectrics, BFO has the large P r and a rather small energy gap E g of 2.67 eV with the direct transition type.…”

Effect of Internal Electric Fields on Charge Carrier Dynamics in a Ferroelectric Material for Solar Energy Conversion

“…Indeed, a photo voltage exceeding 16 V has been reported in a photovoltaic device employing BiFeO 3 , attributed to additive band bending contributions from multiple ferroelectric domains. [ 18 ] Band bending associated with the spontaneous polarization of a ferro electric material, therefore, has the potential to substantially impact on the charge carrier lifetimes, and thus the efficiency, of solar energy conversion devices.…”

One‐Dimensional Ferroelectric Nanostructures: Synthesis, Properties, and Applications

“…The FE‐PV effect is distinctly different from the typical photovoltaic (PV) effect in semiconductor p–n junctions in that the polarization electric field is the driving force for the photocurrent in FE‐PV devices, in which a homogeneous ferroelectric material is used as a light absorbing layer 165. Thus, there exists two unique and important characteristics of FE‐PV devices, one is that the photocurrent direction can be switched by changing the spontaneous polarization direction of a ferroelectric material with the electric field, the other is the anomalous photovoltaic (APV) effect, i.e., the output photovoltage, which is proportional to the magnitude of electric polarization and electrode spacing,166 can be a few orders of magnitude larger than the band gap of the ferroelectric materials 167…”