Photo-ferroelectric oxides for photovoltaic applications: Insights, challenges and opportunities

• Photo-ferroelectric materials oxides thin films for photovoltaic applications. • Enhance the PCE of FE-PV through bandgap tuning, strain engineering and domain wall. • Integration of BPVE in classical SC-PV. • BPVE with high photovoltage exceeding the bandgap of material. Ferroelectric materials have been known for decades for their exclusive non-centrosymmetric crystalline structures and their unique property of switchable spontaneous polarisation; an essential feature used in many modern electronic applications. Ferroelectric materials can also exhibit the bulk photovoltaic effect (BPVE) in an additional process than conventional semiconductors. In recent decades, interest in these phenomena has increased and there is the prospect of improving photovoltaic conversion efficiency to exceed that of commercial solar cells based on Si p-n junctions. The photovoltage that can be generated in ferroelectrics can far exceed the bandgap of the photoactive material, thus circumventing the Schokley-Queisser limit of p-n junctions. In this review, the background, state of the art and advances in the field of low bandgap ferroelectric oxide materials are examined to develop the next generation of ferroelectric materials for solar energy conversion. Firstly, the scientific understanding of the mechanism behind BPVE is assessed. Then, the effects of material synthesis and modifications to improve the band gap, polarisation and ferroelectric domain properties are analysed to discuss the challenges, limitations and perspectives of the topic.