Ultra low band gap α,β-unsubstituted BODIPY-based copolymer synthesized by palladium catalyzed cross-coupling polymerization for near infrared organic photovoltaics
Abstract:A new ultra low band gap (LBG) α,β-unsubstituted BODIPY-based conjugated polymer has been synthesized by conventional cross coupling polymerization techniques (Stille cross coupling) for the first time. The polymer exhibits a panchromatic absorption spectrum ranging from 300 nm to 1100 nm and an optical band gap (Eg opt ) of 1.15 eV, suitable for near infrared (NIR) organic photovoltaic applications as electron donor. Preliminary power conversion efficiency (PCE) of 1.1 % in polymer:[6,6]-phenyl-C71-butyric ac… Show more
“…In practice, the development of BODIPY-based organic semiconductors and especially those of the α,β -unsubstituted forms has so far lagged behind that of other π-deficient units, mainly because of stability issues during the synthesis. However, thanks to a recently developed synthetic protocol, stable α,β -unsubstituted BODIPYs functionalized solely on the meso position can be successfully produced and integrated into more complex structures 35 .Figure 1( a ) Device structure, including details of the different layers, ( b ) chemical structure of F8BT and NIRBDTE, ( c ) the energy levels of F8BT and NIRBDTE and ( d ) the related band diagram (both extracted from the cyclic voltammetry data) of the emitting blend F8BT:NIRBDTE as active layer (in their isolated conditions, before heterostructure formation) with the density-functional theory (DFT) HOMO and LUMO wavefunction plots of NIRBDTE (calculated with the B3LYP/6-31 G(d,p) basis set). The effective HOMO and LUMO of NIRBDTE are those of the part indicated in blue, but we also illustrate in red the local electronic structure of the BODIPY moieties to emphasise the insight gained from DFT calculations of the frontier levels charge distribution, and the “hole-funnelling” effects towards the central bithienyl.
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We take advantage of a recent breakthrough in the synthesis of α,β-unfunctionalised 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) moieties, which we symmetrically conjugate with oligothienyls in an unexpectedly stable form, and produce a “metal-free” A-D-A (acceptor-donor-acceptor) oligomer emitting in the near-infrared (NIR) thanks to delocalisation of the BODIPY low-lying lowest unoccupied molecular orbital (LUMO) over the oligothienyl moieties, as confirmed by density functional theory (DFT). We are able to retain a PL efficiency of 20% in the solid state (vs. 30% in dilute solutions) by incorporating such a dye in a wider gap polyfluorene matrix and demonstrate organic light-emitting diodes (OLEDs) emitting at 720 nm. We achieve external quantum efficiencies (EQEs) up to 1.1%, the highest value achieved so far by a “metal-free” NIR-OLED not intentionally benefitting from triplet-triplet annihilation. Our work demonstrates for the first time the promise of A-D-A type dyes for NIR OLEDs applications thereby paving the way for further optimisation.
“…In practice, the development of BODIPY-based organic semiconductors and especially those of the α,β -unsubstituted forms has so far lagged behind that of other π-deficient units, mainly because of stability issues during the synthesis. However, thanks to a recently developed synthetic protocol, stable α,β -unsubstituted BODIPYs functionalized solely on the meso position can be successfully produced and integrated into more complex structures 35 .Figure 1( a ) Device structure, including details of the different layers, ( b ) chemical structure of F8BT and NIRBDTE, ( c ) the energy levels of F8BT and NIRBDTE and ( d ) the related band diagram (both extracted from the cyclic voltammetry data) of the emitting blend F8BT:NIRBDTE as active layer (in their isolated conditions, before heterostructure formation) with the density-functional theory (DFT) HOMO and LUMO wavefunction plots of NIRBDTE (calculated with the B3LYP/6-31 G(d,p) basis set). The effective HOMO and LUMO of NIRBDTE are those of the part indicated in blue, but we also illustrate in red the local electronic structure of the BODIPY moieties to emphasise the insight gained from DFT calculations of the frontier levels charge distribution, and the “hole-funnelling” effects towards the central bithienyl.
…”
We take advantage of a recent breakthrough in the synthesis of α,β-unfunctionalised 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) moieties, which we symmetrically conjugate with oligothienyls in an unexpectedly stable form, and produce a “metal-free” A-D-A (acceptor-donor-acceptor) oligomer emitting in the near-infrared (NIR) thanks to delocalisation of the BODIPY low-lying lowest unoccupied molecular orbital (LUMO) over the oligothienyl moieties, as confirmed by density functional theory (DFT). We are able to retain a PL efficiency of 20% in the solid state (vs. 30% in dilute solutions) by incorporating such a dye in a wider gap polyfluorene matrix and demonstrate organic light-emitting diodes (OLEDs) emitting at 720 nm. We achieve external quantum efficiencies (EQEs) up to 1.1%, the highest value achieved so far by a “metal-free” NIR-OLED not intentionally benefitting from triplet-triplet annihilation. Our work demonstrates for the first time the promise of A-D-A type dyes for NIR OLEDs applications thereby paving the way for further optimisation.
“…In 2015, Squeo et al published the preparation of TBDPTV . This latter polymer is composed of meso ‐thiophene‐BODIPY and bis(thiophen‐2‐yl)ethene units linked by Stille cross‐coupling reaction.…”
International audienceAdvances in the synthesis and application of highly efficient polymers and small molecules over the last two decades have enabled the rapid advancement in the development of organic solar cells and photovoltaic technology as a promising alternative to conventional solar cells, based on silicon and other inorganic semiconducting materials. Among the different types of organic semiconducting materials, porphyrins and BODIPY-based small molecules and conjugated polymers attract high interest as efficient semiconducting organic materials for dye sensitized solar cells and bulk heterojunction organic solar cells. The highest power conversion efficiency exceeding 9% has been reported so far for porphyrin small molecules and 8.60% for conjugated polymers based on porphyrins. On the other hand, small molecules and conjugated polymers based on BODIPY moiety have been successfully used as donor materials for solution processed bulk heterojunction organic solar cells, and the resultant devices showed power conversion efficiencies exceeding 5.5%. In this article, the development of molecular design of porphyrins and BODIPY small molecules and polymers for bulk heterojunction organic solar cells are reviewed, and a guideline for the structure-performance relationship is provided
“…In the past two decades, as fullerene acceptors were widely used, more attention have been attracted by low bandgap polymers because of the weak fullerene absorption in visible light region . However, nonfullerene acceptors exhibit very good absorption from 500 to 800 nm (some of them can even reach 1000 nm).…”
Recently, an increasing number of researchers have begun to focus on developing nonfullerene acceptors, so it is very important to synthesize new polymers that are compatible with nonfullerene acceptors. Besides, wide‐ or medium‐bandgap polymer donors could be better to match narrow nonfullerene acceptors. The design of medium‐bandgap (MBG) polymer donors and their application in organic photovoltaics (OPVs) play an important part in the improvement of OPV device performance. This review summarizes the photovoltaic performance of MBG polymers that have been reported during the last decade. Furthermore, their structure–property relationships and device performance are discussed. On the basis of analyzing many polymer structures, guidance toward the design of novel photovoltaic materials might be helpful to understand the basic OPV mechanism and the path towards commercialization.
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