The origin and evolution of Y6 structure

Peripheral halogenation engineering controls molecular stacking to enable highly efficient organic solar cells

“…Given the dominant molecular packing mode of end unit to end unit (E/E) observed in the single crystals of ITIC 51,52 and F 53,54 series NFAs, significantly improved photodynamic processes and even PCEs have been generally achieved after halogen substitution on the end groups. 55,56 However, in a typical Y6 single crystal, [57][58][59] the central unit of benzothiadiazole (BT) is also largely involved in molecular packing and leads to a much more effective three-dimensional nanoscale network, which is significantly different from those in ITIC and F series NFAs. Based on these results, it is expected that the degree of molecular packing affected by the halogenation on central units may be no less than that of on end groups in Y-series NFAs, and further improvement of OSCs possibly could be rendered if suitable halogenation can be also conducted on central units of high-performance Y-series NFAs.…”

New Type of Polymerized Small A-D-A Acceptors Constructed by Conjugation Extension in the Branched Direction

“…22,23 However, this pathway to construct PSMAs will bring about several inherent defects: (i) inferior intermolecular packings; the efficient molecular packings through terminal groups have been proven as the dominant packing mode in nonfullerene SMAs, which could be clearly concluded from lots of single-crystal structures of SMAs. 4,24,25 However, the chemical structure, electrondeficient property, and steric hindrance of terminal groups will be greatly changed when polymerizing with other linker units, such as thiophene or its derivatives, through terminal groups of SMAs. 26−28 This will inevitably damage the already perfect molecular packings formed by nonfullerene SMAs and, thus, decrease the PCEs of all-PSCs.…”

“…At present, almost all the high-performance PSMAs are constructed by directly polymerizing Y-series nonfullerene SMAs. , In the aspect of molecular structures, Y-series nonfullerene SMAs can be divided into three components: fused-ring central donors, electron-deficient terminals, and flexible branched chains. , Since the active sites for polymerization reactions usually locate at the electron-deficient terminals, it is not surprising that nearly all the high-performance PSMAs currently are constructed by polymerization through terminal units. , However, this pathway to construct PSMAs will bring about several inherent defects: (i) inferior intermolecular packings; the efficient molecular packings through terminal groups have been proven as the dominant packing mode in nonfullerene SMAs, which could be clearly concluded from lots of single-crystal structures of SMAs. ,, However, the chemical structure, electron-deficient property, and steric hindrance of terminal groups will be greatly changed when polymerizing with other linker units, such as thiophene or its derivatives, through terminal groups of SMAs. − This will inevitably damage the already perfect molecular packings formed by nonfullerene SMAs and, thus, decrease the PCEs of all-PSCs. (ii) Decreased halogen density; the polymerization through terminal units of SMAs will consume a halogen atom on molecular backbones.…”

A polymer acceptor with grafted small molecule acceptor units for high-efficiency organic solar cells

“…(1) Decreased intermolecular packing interaction: the intermolecular packing between electron withdrawing end groups has proved to be an essential and crucial packing mode in non-fullerene SMAs, which benets the formation of efficient charge transport channels. [31][32][33] However, aer polymerizing with other linkers, the packing mode of the end groups in the original SMAs will be signicantly changed. Especially, in many cases, the skeleton planarity of the polymer acceptors cannot be ensured owing to the twist conformation between the end groups of SMAs and the linker units, which will also be unfavourable for the intermolecular packing and corresponding device photovoltaic performances.…”