Impact of End-Group\nChlorination on Charge Generation\nand Recombination Patterns in Organic Solar Cells with Wide-Band-Gap\nAcceptors

Cl-substituted nonfullerene acceptors (NFAs) exhibit\nplanar conformations\nthat can enhance molecular packing and electronic coupling. In this\nstudy, a chlorinated wide-band-gap NFA, YO-TCl, with tetrahalogen-substituted\nend groups, is introduced and compared with ZY-4Cl to systematically\nexamine how the Cl-substituted end groups impact the blend morphology,\ncharge generation, and extraction in their correlated bulk heterojunction\n(BHJ) devices. Compared to ZY-4Cl, with two chlorine atoms in each\nend group, YO-TCl possesses a downshifted highest occupied molecular\norbital (HOMO) and red-shifted absorption. Organic solar cells (OSCs)\nare fabricated using PBDB-T as donors and the two wide-band-gap NFAs\nas acceptors. From ZY-4Cl to YO-TCl, power conversion efficiencies\n(PCEs) from 7.6 to 13.2% are obtained, which can be attributed to\nthe better film morphology of the YO-TCl-based bulk heterojunction\n(BHJ) film. Taking into account the efficiency disparities between\nZY-4Cl- and YO-TCl-based BHJ devices, we specifically focus on investigating\nthe molecular packing properties of the organic films and their effects\non charge transport, recombination, and extraction in the resulting\nBHJ devices. Our analyses reveal that ZY-4Cl- and YO-TCl-based devices\nexhibit significantly different charge generation, recombination,\nand extraction characteristics, which stem from distinct aggregation\nand phase distribution within the BHJ blend films.