Unification of the best piezoelectric and photovoltaic properties in a single photoferroelectric material

Introduction

The piezoelectric (PE) effect is the core electromechanical coupling function widely used in sensors, actuators, and transducers for various industrial sectors. The photovoltaic (PV) effect produces green electricity from solar energy.

Current State of Materials

To date, materials showing strong PE and efficient PV properties are separate families of oxide perovskites and narrow band gap semiconductors, respectively. This project aims to unify these PE and PV performances by making new photoferroelectric materials.

Challenges in Photoferroelectrics

Photoferroelectrics can be both ferroelectric and photovoltaic. However, several challenges hinder them from being practically used as single, integrated PE-PV materials:

1. Not all good ferroelectrics show strong PE responses.
2. The strong piezoelectrics have wide band gaps, unable to absorb visible light.
3. The photovoltaic energy conversion efficiencies (PCE) of photoferroelectrics are far below those of semiconductor solar cells.

Project Objectives

To address the challenges, this project will:

1. Start with the oxide perovskite compositions showing the record PE properties. These compositions will be engineered by doping to reduce the band gaps and thus to absorb the entire visible light while maintaining the original PE properties.
2. Grow the engineered compositions into single crystals to further boost the PE properties and to form stacked domain walls.
3. Generate photovoltages from the stacked domain walls that can add up domain by domain, producing an ultra-high net photovoltage in the material.
4. Boost the efficient photocurrent generation in the domain walls by ensuring complete light absorption, achieved by having the single crystal thickness equal to the light penetration depth, pushing the PCE to the level of semiconductor solar cells.

Expected Outcomes

The results are expected to trigger revolutions in mechano-solar-electric multi-energy converters for emerging applications such as the Internet of Things that require long lifespan and miniaturization.