Efficient Indoor Light Harvesting with High Band Gap Perovskite and Sodium-Ion Battery

Integrating storage technologies in renewable energy systems of the future is one of the most important problems of the moment. Recent development trends in small scale consumer electronics towards implementing “Internet of Things” and smart house/smart cities concepts make it imperative to have cheap, wireless power solutions for electronics that operate all day. The combination of photovoltaic (PV) devices with rechargeable batteries represents a viable strategy for powering such low power electronic devices. With the increasing use of indoor LED (light emitting diode) lighting worldwide, the matching spectrums of LED output and the absorption spectrum of lead halide perovskite solar cells (PSC) affords an opportunity to reuse emitted light with high efficiency to feed low power electronics. Recently, lead halide perovskite cells and modules have demonstrated efficiencies under artificial lighting of more than 30 % [1] with a record of 40.1 % achieved with an extra thick absorber layer [2]. The main reason is the very close overlap of the external quantum efficiency in lead halide perovskite solar cells with the emission spectrum of an LED lamp. However, there are not many publications showing a combination of perovskite-battery devices working efficiently under low light LED illumination intensities.<br/>The aim of the work is to demonstrate a successful and highly efficient energy harvesting and storage under a wide range of light emitting diode (LED) illumination intensities by applying lead halide perovskite solar module directly coupled to a high-rate capable next generation sodium ion battery. Direct coupling of PV and batteries require fabrication of perovskite solar module with tailored current-voltage (IV) characteristic to match battery voltage under target irradiance conditions. A 3-cell perovskite module with CH₃NH₃Pb(I_0.8Br_0.2)₃ absorber layer and fullerene electron transport layer were fabricated with a conversion efficiency of 17.8 %, with a fill factor of 81.3 %, short-circuit current density of 5.91 mAcm^-2 and open-circuit voltage of 3.71 V under AM.1.5 illumination. To test the PSC modules for indoor battery charging under LED lighting a sodium ion battery with metallic sodium anode and cathode made from sodium titanium phosphate (NaTi₂(PO₄)₂) coated onto sheets of carbon nano-felt (NTP@CNF) was chosen due to its high charge rate capability, low charge-discharge overpotential and distinct charge and discharge voltage plateau. LED illumination intensity was attenuated by using neutral density filters.<br/>High efficiency indoor charging of advanced sodium ion battery based on sodium titanium phosphate (NaTi₂(PO₄)₂) coated onto sheets of carbon nano-felt coupled with a perovskite solar module with CH₃NH₃Pb(I_0.8Br_0.2)₃ absorber layer under LED illumination was demonstrated. We have directly coupled both devices without any power electronics and achieved overall PV-Battery efficiency of 24.3% at 300 lx LED lightning. Under target LED illuminance of 300 lx, the perovskite solar cell shows PCE of 29.4%, and coupling factor of 0.87, and roundtrip battery efficiency of 94.9 % [3].<br/><br/>References<br/>[1] Cheng, R.; et al., Advanced Energy Materials. 2019, 9, 1901980. https://doi.org/10.1002/aenm.201901980<br/>[2] He, X.; et al., Advanced Materials. 2021, 33, 2100770. https://doi.org/10.1002/adma.202100770<br/>[3] Kin L.C-.; et al. Cell Reports Physical Science 2022, 3, 101123.