A selenium-substituted core and a synergistic regioisomer-free monomethylated terminal enable methylated acceptors with high efficiency and low energy loss in binary organic solar cells

TY - JOUR

T1 - A selenium-substituted core and a synergistic regioisomer-free monomethylated terminal enable methylated acceptors with high efficiency and low energy loss in binary organic solar cells

AU - Yang, Can

AU - Liu, Tao

AU - Liu, Kai Kai

AU - Yan, Lu

AU - Mahmood, Asif

AU - Kang, Min Gyu

AU - Rong, Hongchen

AU - Woo, Han Young

AU - Wang, Jin Liang

N1 - Publisher Copyright: This journal is © The Royal Society of Chemistry, 2026.

PY - 2026/5/21

Y1 - 2026/5/21

N2 - Selenium substitution and methyl modification of small molecular acceptors (SMAs) are often utilized for developing efficient organic solar cells (OSCs); however, their synergistic effects on the trade-off between device parameters have rarely been investigated. Herein, a pair of A–D–A-type FR-SMAs (IT-M-γ and BIT-M-γ) with regioisomer-free monomethylated IC, comprising fused-ring indacenodithieno[3,2-b]thiophene and indacenodithieno[3,2-b]selenophene as their core units, were synthesized using the synergistic selenium-substituted core and regio-specific methylated terminal strategies, respectively. BIT-M-γ showed a red-shifted absorption, more suitable energy levels, and a planar molecular conformation compared with IT-M-γ owing to the introduction of the selenium atom. These regioisomer-free monomethylated single crystals were successfully obtained for the first time. Compared to IT-M-γ, the BIT-M-γ single crystal forms a novel 2D linear stacked structure via stronger J-aggregation and multiple intermolecular interactions, leading to increased electron mobility and excellent crystallinity in neat films. The PM6:BIT-M-γ blend film exhibits favorable phase separation with a more ordered face-on orientation, tighter molecular packing, enhanced crystallinity, and high and balanced carrier mobility. Consequently, PM6:BIT-M-γ-based binary OSCs achieve a higher PCE of 12.56% with a lower Eloss of 0.509 eV, compared to IT-M-γ-based devices with a PCE of 11.06% with an Eloss of 0.586 eV. More excitingly, the impressive PCE with minimal Eloss represents the best results for A–D–A type FR-SMAs with methylated terminals in binary OSCs. Our work demonstrates that a synergistic strategy by combining the selenium-substituted central core with the regioisomer-free monomethylated terminal has great potential in optimizing crystal packing and further improving the PCE with minimal Eloss of binary OSCs.

AB - Selenium substitution and methyl modification of small molecular acceptors (SMAs) are often utilized for developing efficient organic solar cells (OSCs); however, their synergistic effects on the trade-off between device parameters have rarely been investigated. Herein, a pair of A–D–A-type FR-SMAs (IT-M-γ and BIT-M-γ) with regioisomer-free monomethylated IC, comprising fused-ring indacenodithieno[3,2-b]thiophene and indacenodithieno[3,2-b]selenophene as their core units, were synthesized using the synergistic selenium-substituted core and regio-specific methylated terminal strategies, respectively. BIT-M-γ showed a red-shifted absorption, more suitable energy levels, and a planar molecular conformation compared with IT-M-γ owing to the introduction of the selenium atom. These regioisomer-free monomethylated single crystals were successfully obtained for the first time. Compared to IT-M-γ, the BIT-M-γ single crystal forms a novel 2D linear stacked structure via stronger J-aggregation and multiple intermolecular interactions, leading to increased electron mobility and excellent crystallinity in neat films. The PM6:BIT-M-γ blend film exhibits favorable phase separation with a more ordered face-on orientation, tighter molecular packing, enhanced crystallinity, and high and balanced carrier mobility. Consequently, PM6:BIT-M-γ-based binary OSCs achieve a higher PCE of 12.56% with a lower Eloss of 0.509 eV, compared to IT-M-γ-based devices with a PCE of 11.06% with an Eloss of 0.586 eV. More excitingly, the impressive PCE with minimal Eloss represents the best results for A–D–A type FR-SMAs with methylated terminals in binary OSCs. Our work demonstrates that a synergistic strategy by combining the selenium-substituted central core with the regioisomer-free monomethylated terminal has great potential in optimizing crystal packing and further improving the PCE with minimal Eloss of binary OSCs.

UR - https://www.scopus.com/pages/publications/105034572954

U2 - 10.1039/d5tc04481b

DO - 10.1039/d5tc04481b

M3 - Article

AN - SCOPUS:105034572954

SN - 2050-7526

VL - 14

SP - 8066

EP - 8076

JO - Journal of Materials Chemistry C

JF - Journal of Materials Chemistry C

IS - 19

ER -