Submerged solar energy harvesting using ferroelectric Ti‐doped BFO‐based heterojunction solar cells

Summary Herein, ferroelectric Ti‐doped BiFeO3 (BFTO) heterojunction photovoltaic (PV) cells are realized for underwater PV applications. In the heterostructure, NiO functions as a transparent wide‐bandgap (3.2 eV) hole transport layer (HTL), whereas BFTO is the visible energy harvester and the highly conductive WS2 behaves as the electron transport layer (ETL). The multijunction PV device with a cell area of 1cm2 revealed a current density (JSC) and an open‐circuit voltage (VOC) of 1.90 mA/cm2 and 1.20 V, respectively, under ambient conditions (before submerging into water). Subsequently, the polydimethylsiloxane (PDMS)‐encapsulated Ag/NiO/BFTO/WS2/ITO PV device was investigated for underwater solar energy harvesting in a shallow tank. For a comparative analysis, the mono‐junction NiO/BFTO and BFTO/WS2 PVs were also evaluated. The results indicated a steady decrease in the efficacy and power density of the cell with depth, and the heterojunction PV has outperformed the single‐junction PVs. As there are spectral variations with increase in depth, the heterostructure seem to have the potential to absorb the overall spectrum as NiO being transparent transmits high energy UV radiations into the device, while BFTO and WS2 layers absorb the visible and NIR spectrum. Therefore, the device though submerged can capture the solar energy efficiently with minimal losses in terms of spectrum and function efficiently. These results establish that the ferroelectric nano‐heterostructured PV devices can be utilized as a power generating source for various low‐power marine‐based sensing applications.