Unraveling the Optoelectronic Exciton Dynamics of NDI (Naphthalene Diimide)-Based Nonfullerene Acceptor with Improved Band Alignment

Nonfullerene acceptors offer tunable optical and electrical properties. They are gaining extensive research attention to enable highly efficient organic solar cells (OSCs) beyond the capabilities of traditional fullerene-based acceptors. This study investigates ultrafast charge transfer and exciton dissociation dynamics within bulk heterojunction (BHJ) systems incorporating the nonfullerene acceptor material N,N′-bis(1-indanyl)naphthalene-1,4,5,8-tetracarboxylic diimide (NDIID). By comparing the performance of poly(3-hexylthiophene) (P3HT):NDIID and poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b′]-dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]-thieno[3,4-b]thiophene-4,6-diyl} (PTB7):NDIID blends to that of traditional [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)-based blends, ultrafast transient absorption spectroscopy (UTAS) unveils the superior charge carrier dynamics facilitated by NDIID, a promising nonfullerene acceptor. The NDIID-containing blends exhibit enhanced charge generation, transport, and collection efficiency, which are attributed to better band alignment, higher electron mobility, accelerated charge transport dynamics (up to 44%), and reduced recombination rates (up to 75%). These improvements are indicative of a significant increase in device efficiency and stability. The introduction of NDIID as a viable alternative to PCBM for nonfullerene acceptors in BHJ organic solar cells represents a crucial step forward in developing high-performance, cost-effective renewable energy technologies.