Space-time visualization of photo-excited carrier dynamics in ferroelectric solar-energy converters by ultrafast electron microscopy

Giant bulk photovoltaic effect in non-centrosymmetric ferroelectric materials is currently gaining tremendous research interest due to its above-bandgap photovoltage and the observed output voltage is around 3-4 orders of magnitude higher than the Si-solar cells. Hence, the ferroelectric photovoltaic response is considered the next-generation photovoltaic device.

However, researchers currently lack a profound understanding of the exact mechanism of the bulk photovoltaic effect, and the proposed mechanisms are contradictory to each other. This, in turn, restricts the progress of the field towards efficient solar cells.

The difficult part of finding the exact mechanism is due to ultrafast carrier dynamics and atomic relaxation times are of the order of 0.1 to 10 femtoseconds, which made it experimentally inaccessible.

At present, the excellent infrastructure and facilities of my host institute dealing with the ultrafast carrier dynamics can record the meticulous dynamics in space-time resolution and hence can provide the exact mechanism towards the above bandgap photovoltage in the ferroelectric system.

Therefore, through this project, we are going to investigate the origin of the anomalous bulk photovoltaic effect in perovskite ferroelectric oxides by filming the ultrafast photo-absorption and subsequent photo-excited carrier relaxation dynamics with femtosecond time resolution and nanometre spatial resolution using laser-driven electron microscopy.

In contrast to the spectroscopic approach, ultrafast electron pulses in a femtosecond electron microscope or diffraction apparatus can provide nanometre spatial and femtosecond temporal resolutions at the same time and hence can provide a movie of evolving electromagnetic field in space and time.

Based on the data generated, a comprehensive physical mechanism will be put forth, which will act as guidance for the selection and design of future ferroelectric systems for an improved photovoltaic response.