Harnessing light in tandem: advanced erbium-polyaniline QD composites for next-generation energy storage

Simultaneous harvesting of sunlight and storing its energy in optoelectronic devices is a scientific challenge. The current work pursues two main goals: (1) to understand the interaction of erbium ions with stable PANI quantum dots (QD, 8 nm), obtained by acid-assisted polymerization method, and (2) to investigate the potential application of Er-PANI:PSS composite as a next-generation energy storage system. PANI QD of 8 nm size is synthesized for the first time, stabilized by PSS and decorated with Er³⁺ ions. FTIR and XPS analyses confirm that no direct erbium-PANI coordination is observed; nevertheless, PANI is likely present in the second coordination sphere of the erbium complex, potentially enabling energy transfer between the PANI π-system and Er³⁺ ions. CV and LSV measurements show that the incorporation of Er³⁺ ions into the composite leads to a marked improvement in electrochemical performance. A further enhancement in areal current was achieved under light irradiation, particularly when using a 655 nm LED, which corresponds to one of the most intense regions of the solar spectrum. The enhanced photoelectrochemical activity is attributed to a synergistic mechanism involving photo-assisted PANI protonation and Er³⁺-mediated charge storage, where Er³⁺ ions create new redox states and facilitate efficient outer-sphere electron transfer, stabilizing charge carriers and boosting photocurrent generation. These findings highlight the promise of Er-PANI:PSS composite for integrated solar energy harvesting and storage technologies.