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

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 the solar energy. 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. Photoferroelectrics can be both ferroelectric and photovoltaic. However, several challenges hinder them from being practically used as single, integrated PE-PV materials: (i) Not all good ferroelectrics show strong PE responses; (ii) The strong piezoelectrics have wide band gaps, unable to absorb visible lights; (iii) The photovoltaic energy conversion efficiencies (PCE) of photoferroelectrics are far below those of semiconductor solar cells. 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 lights whilst maintaining the original PE properties. (2) The engineered compositions will be grown to single crystals to further boost the PE properties and to form stacked domain walls. (3) The stacked domain walls will generate photovoltages that can add up domain by domain, producing an ultra high net photovoltage in the material. (4) The efficient photocurrent generation in the domain walls will be boosted by the complete light absorption resulted from the single crystal thickness equal to the light penetration depth, pushing the PCE to the level of semiconductor solar cells. The results are expected to trigger revolutions in mechano-solar-electric multi-energy converters for emerging applications such as Internet of Things that require long lifespan and miniaturization.