Covalent Photo-crosslinking of Diketopyrrolopyrrole based Polymeric Layer for Cutting-Edge Near-IR Absorption and DSSC Performance

Abstract

We have developed a novel solvent-free approach for the synthesis and photo cross-linking cycloaddition of diketopyrrolopyrrole (DPP)-based semiconducting polymers, tailored with carbazole side chains incorporating linear octene (DPP-OCT-CBZ) and cyclic vinyl benzyl (DPP-VC-CBZ) spacers. Utilizing UV light (365 nm), these materials undergo photopolymerization cyclo-addition, resulting in robust film characterized by extended UV absorption up to the near-infrared region (1100 nm) and enhanced thermal stability up to 400 ºC. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the formation of cross-linked structures while 1H-NMR and GPC confirms structure of polymers, while morphological uniformity and mechanical rigidity were verified through Atomic Force Microscopy (AFM). Importantly, these materials demonstrate exceptional barrier properties against moisture, evidenced by improved water contact angles. When integrated as barrier layers in DSSCs with N719 dye, DPP-OCT-CBZ-C particularly exhibited a remarkable power conversion efficiency (PCE) of 18.2% under illumination of 800 lux and 7.28% under 1 Sun. This efficiency is attributed to the superior alignment of the linear octene chains with the DSSC layers, effectively suppressing back electron transfer. Our findings highlight the potential of DPP-based polymers in advancing the performance and durability of organic electronic devices, offering a promising avenue for the design of new materials for energy conversion and storage applications.