Unraveling the Optoelectronic\nExciton Dynamics of\nNDI (Naphthalene Diimide)-Based Nonfullerene Acceptor with Improved\nBand Alignment

Nonfullerene acceptors offer tunable optical and electrical\nproperties.\nThey are gaining extensive research attention to enable highly efficient\norganic solar cells (OSCs) beyond the capabilities of traditional\nfullerene-based acceptors. This study investigates ultrafast charge\ntransfer and exciton dissociation dynamics within bulk heterojunction\n(BHJ) systems incorporating the nonfullerene acceptor material <i>N</i>,<i>N</i>′-bis(1-indanyl)naphthalene-1,4,5,8-tetracarboxylic\ndiimide (NDIID). By comparing the performance of poly(3-hexylthiophene)\n(P3HT):NDIID and poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-<i>b</i>:4,5-<i>b</i>′]-dithiophene-2,6-diyl-<i>alt</i>-3-fluoro-2-[(2-ethylhexyl)carbonyl]-thieno[3,4-<i>b</i>]thiophene-4,6-diyl} (PTB7):NDIID blends to that of traditional\n[6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PCBM)-based\nblends, ultrafast transient absorption spectroscopy (UTAS) unveils\nthe superior charge carrier dynamics facilitated by NDIID, a promising\nnonfullerene acceptor. The NDIID-containing blends exhibit enhanced\ncharge generation, transport, and collection efficiency, which are\nattributed to better band alignment, higher electron mobility, accelerated\ncharge transport dynamics (up to 44%), and reduced recombination rates\n(up to 75%). These improvements are indicative of a significant increase\nin device efficiency and stability. The introduction of NDIID as a\nviable alternative to PCBM for nonfullerene acceptors in BHJ organic\nsolar cells represents a crucial step forward in developing high-performance,\ncost-effective renewable energy technologies.