PV-based self-powered IoT nodes: using PVK/Si tandem solar cells for synergetic underwater energy harvesting and water depth sensing or VLC reception

Performing sensing and/or communication in underwater conditions is critical in many related applications; underwater environments are often remote or hardly accessible, so self-powered systems for autonomous operation would in general be particularly advantageous. Two proof-of-concept examples for self-powered PV-based IoT systems dedicated to water depth sensing and to underwater VLC (Visible Light Communication) reception are hereby presented. A 4-terminal PVK/Si (perovskite/silicon) tandem solar cell, where the two sub-cells are only spectrally coupled but electrically independent, allows to effectively decouple the sub-cell current output. This also unlocks a complementary synergy by taking advantage of the different responses of the two sub-cells to different parts of the incident light irradiance spectrum. In fact, while both are able to harvest energy and perform sensing or signal reception functions, the PSC sub-cell shows to be much better suited for effective and reliable energy harvesting at varying depths, on account of its absorption being most aligned with the maximum transmittance range of water, while the Si sub-cell instead is inherently much better suited for sensing or signal reception functions, on account of its superior response sensitivity, range and speed, compared to organic/hybrid-based PV cells such as PSCs. By appropriately accounting for the geometry and layout of the system with respect to the position of the Sun throughout the day/year, aside from being able to harvest energy, a correction algorithm can in theory use geolocation and device reference parameters to also relate the tracked current response and output with the actual depth of the water mass directly above the system. Instead, when using such system as a self-powered underwater VLC receiver coupled with a white LED VLC transmitter, aside from effectively receiving the VLC transmitted modulated signal, the system can harvest energy effectively form the transmitted sunlight or potentially even just from the incident LED light.