Beta-alanine as a Dual Modification Additive in Organic Solar Cells

This work presents a novel approach to modify the interface of organic solar cells（OSCs）by using beta-alanine（β-alanine）which has a hydroxyl（—OH）/carboxyl group（—COOH）group on one side and amine（—NH₂）on the other side. As a dual modifier approach，β-alanine was applied to both the hole-transporting layer（HTL，PEDOT∶PSS）and electron-transporting layer（ETL）；PFN-Br was added in the same device through a simple solution-processed technique，resulting in the synthesis of new interface layers. β-alanine is soluble in polar aqueous solvents，and their soluble components in this work are methanol and water. Dual modification approach improved the power conversion efficiency（PCE）of PM6∶Y6 solar cells，increasing from 14.99% to 15.78% among with a single-sided approach. The hydrophobicity of both layers was enhanced as confirmed by contact angle and FTIR measurements，which blocked moisture and oxygen from interacting with their respective electrodes. The surface morphology was analyzed using AFM. The results showed that the amine group of β-alanine interacted with the —SO^-₃ group of PSS as well as with the bromine halogen（Br^‒）ion of PFN-Br，which reduced their concentration which elevated the hydrophobicity and improved the stability of the OSCs. Furthermore，the carrier mobilities for both the modified devices were improved，which was confirmed by the space-charge-limit current （SCLC）measurements.