High-Performance Non-Fullerene Acceptor Derived from Diathiafulvalene Wings for Solution-Processed Organic Photovoltaics

Abstract

A solution-processable small-molecule nonfullerene electron acceptor BAF-2HDT (7,7′-(9,9-didecyl-9H-fluorene-2,7-diyl)bis(4-((4,5-bis(hexylthio)-1,3-dithiol-2 ylidene)methyl)benzo[c][1,2,5]-thiadiazole) bearing hexadiathiafulvalene (HDT) wings as end groups has been synthesized for bulk heterojunction organic photovoltaics. The molecule shows broad absorption in the 300−600 nm range with a molar extinction coefficient (ε) of 9.32 × 10 4 M −1 ·cm −1 exceeding to that of [6,6]-phenyl-C 71 -butyric acid methyl ester of 2.8 × 10 4 M −1 ·cm −1 at 461 nm. The HOMO and LUMO energy levels of the molecule are found to be −5.69 and −3.58 eV, respectively which is compatible with low band gap high-performance polymers such as poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD). Photoluminescence-quenching measurements confirm that the molecule BAF-2HDT has excellent electron-accepting capability. The organic solar cells made from BAF-2HDT blending with conjugated polymer donor PffBT4T-2OD exhibit a power conversion efficiency of 7.13% with high V oc of 0.77 V, J sc of 14.64 mA·cm −2 , and FF of 0.64. The design and development of such nonfullerene acceptors with high ε may be key to further development of high-performance and costeffective solution-processed organic solar cells.

Synthesis of a tetrazine–quaterthiophene copolymer and its optical, structural and photovoltaic properties

“…This was achieved by attaching (2-octyl-)dodecyl side chains in the 4-position on the flanking thiophene rings with respect to the acceptor unit, while bithiophene was used as donor. In addition to fullerene-based devices, NFA-based solar cells with promising PCE values of up to 9% have been reported using PffBT4T‐2OD (poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐ alt ‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′′′‐diyl)]) as polymeric donor in the absorber layer [ 17 , 18 ].…”

Effectiveness of Solvent Vapor Annealing over Thermal Annealing on the Photovoltaic Performance of Non-Fullerene Acceptor Based BHJ Solar Cells

“…Knoevenagel condensation between dicyano-N-hexylrhodanine and aryl dialdehyde intermediate (BAF-2CHO) to afford the BAF-4CN in dark red color. Th e BAF-2HDT was obtained as dark pink color through Horner–Wittig reaction between intermediate BAF-2CHO and HDT 27,28 . BAF-4CN and BAF-2HDT are readily soluble in common organic solvents, such as dichloromethane (DCM), tetrahydrofuran (THF), chlorobenzene (CB), o-dichlorobenzene (o-DCB) and chloroform at room temperature.…”

“…In this set of devices, the photo-active layer was thermally annealed (TA) at 80 °C for 15 minutes after spin casting. In order to improve the device performance further, we have investigated the effect of vacuum annealing (VA) and solvent vapor annealing (SVA) treatments on the blend films 27,28 . The VA was carried out inside the antechamber of glove box for the duration of 2 h. For the SVA method, films were separately put into a Petri dish with few drops of CB around it for 30 min.…”

“…Our group has designed and synthesized two calamitic type SMNFAs coded as BAF-4CN and BAF-2HDT (Fig. 1) having dialkylated fluorene as the core, the electron accepting unit benzothiadiazole (BT) attached to the weak electron donating core fluorene and terminated with dicyano-N-hexylrhodanine (2CN) in the case of BAF-4CN and diathiafulvalene (HDT) in the case of BAF-2HDT for use in solution processable OPV cells 27,28 . Introduction of dicyano-n-hexylrhodanine and HDT substituent as end-capping agents effectively lowers the LUMO energy level of the resultant molecules, increases the light absorption properties, facilitates delocalization of π -electrons, and reduces the band gap and increases the charge transfer mobility by extending linear conjugation throughout the molecular backbone.…”

Conductivity and Density of States of New Polyphenylquinoline

“…For preparing organic light emitting diodes and photovoltaic cells, various types of electron–acceptor compounds such as perylene diimide, diketopyrrolopyrrole, benzothiadiazole are introduced into the photoactive materials [9,17,18,19,20]. 2,1,3-Benzothiadiazole (DBT), which either enhances photophysical properties of a polymer chain or serves as a dopant molecule, is of a special compound in this list [19].…”