Organic solar cells based on acceptor-p-acceptor(A-π-A) electron acceptors have attracted intensive attention due to their increasing and record power conversion efficiencies. To date, almost all of the reported A-π...Organic solar cells based on acceptor-p-acceptor(A-π-A) electron acceptors have attracted intensive attention due to their increasing and record power conversion efficiencies. To date, almost all of the reported A-π-A electron acceptors are based on aromatic p structures. Here, we have investigated the impact of anti-aromatization of the p-bridges on the optoelectronic properties of A-π-A electron acceptors by(time-dependent) density functional theory. Our calculations show that besides the frontier molecular orbitals corresponding to the aromatic p-bridge based acceptors("aromatic" acceptors),additional and unique occupied and unoccupied frontier orbitals are found for the acceptors based on the anti-aromatic p-bridges("anti-aromatic" acceptors). Moreover, by tuning isomeric structures of the p-bridges(e.g., fusion orientations or linking positions of thiophene moieties), the optical excitation energies for the transition between the additional occupied and unoccupied levels turn to be close to or substantially lower with respect to those for the transition between the "aromatic" frontier orbitals. The optical absorption of the "anti-aromatic" acceptors is thus either stronger or broader than the "aromatic"acceptors. Finally, the reorganization energies for electron transport are tunable and dependent on the p-bridge structures. These results indicate a great potential of "anti-aromatic" electron acceptors in organic photovoltaics.展开更多
With the development of photovoltaic materials, especially the small molecule acceptors(SMAs), organic solar cells(OSCs)have made breakthroughs in power conversion efficiencies(PCEs). However, the stability of high-pe...With the development of photovoltaic materials, especially the small molecule acceptors(SMAs), organic solar cells(OSCs)have made breakthroughs in power conversion efficiencies(PCEs). However, the stability of high-performance OSCs remains a critical challenge for future technological applications. To tackle the inherent instability of SMA materials under the ambient conditions, much effort has been made to improve OSCs stability, including device modification and new materials design. Here we proposed a new electron acceptor design strategy and developed a “quasi-macromolecule”(QM) with an A-π-A structure,where the functionalized π-bridge is used as a linker between two SMAs(A), to improve the long-term stability without deteriorating device efficiencies. Such type of QMs enables excellent synthetic flexibility to modulate their optical/electrochemical properties, crystallization and aggregation behaviors by changing the A and π units. Moreover, QMs possess a unique long conjugated backbone combining high molecular weight over 3.5 k Da with high purity. Compared with the corresponding SMA BTP-4F-OD(Y6-OD), the devices based on newly synthesized A-π-A type acceptors QM1 and QM2 could exhibit better device stability and more promising PCEs of 17.05% and 16.36%, respectively. This kind of “molecular-framework”(A-π-A)structure provides a new design strategy for developing high-efficiency and-stability photovoltaic materials.展开更多
For bulk-heterojunction organic solar cells, the morphology of the blend films highly influence the exciton dissociation and charge transport process. In this work, two novel A-π-D-π-A(A represents the acceptor unit...For bulk-heterojunction organic solar cells, the morphology of the blend films highly influence the exciton dissociation and charge transport process. In this work, two novel A-π-D-π-A(A represents the acceptor unit and D represents the donor unit) backbone structure small molecular electron donors based on two dimensional conjugated naphtho[1,2-b:5,6-b']dithiophene(NDT) with different end alkyl chains, named as NDT-3T-EH and NDT-3T-O, have been designed and synthesized. The photovoltaic property of NDT-3T-O-based device is better than that of the NDT-3T-EH and the best efficiency reaches 7.06%, and the photovoltaic property of NDT-3T-EH reaches 6.11%. The difference in the performance should be attributed to the different morphology and phase separation resulted from the different crystallinity and aggregation ability of two donors. The results demonstrate that the optimized end alkyl chains can be used to design A-π-D-π-A backbone structure small molecular electron donors for smallmolecule organic solar cells.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51773208)the Ministry of Science and Technology of China (No. 2014CB643506)the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB12020200).
文摘Organic solar cells based on acceptor-p-acceptor(A-π-A) electron acceptors have attracted intensive attention due to their increasing and record power conversion efficiencies. To date, almost all of the reported A-π-A electron acceptors are based on aromatic p structures. Here, we have investigated the impact of anti-aromatization of the p-bridges on the optoelectronic properties of A-π-A electron acceptors by(time-dependent) density functional theory. Our calculations show that besides the frontier molecular orbitals corresponding to the aromatic p-bridge based acceptors("aromatic" acceptors),additional and unique occupied and unoccupied frontier orbitals are found for the acceptors based on the anti-aromatic p-bridges("anti-aromatic" acceptors). Moreover, by tuning isomeric structures of the p-bridges(e.g., fusion orientations or linking positions of thiophene moieties), the optical excitation energies for the transition between the additional occupied and unoccupied levels turn to be close to or substantially lower with respect to those for the transition between the "aromatic" frontier orbitals. The optical absorption of the "anti-aromatic" acceptors is thus either stronger or broader than the "aromatic"acceptors. Finally, the reorganization energies for electron transport are tunable and dependent on the p-bridge structures. These results indicate a great potential of "anti-aromatic" electron acceptors in organic photovoltaics.
基金supported by the National Natural Science Foundation of China (52125306, 21875286, 22005347)the Natural Science Foundation of Hunan Province (2021JJ20068)the National Key Research and Development Program of China (2017YFA0206600)。
文摘With the development of photovoltaic materials, especially the small molecule acceptors(SMAs), organic solar cells(OSCs)have made breakthroughs in power conversion efficiencies(PCEs). However, the stability of high-performance OSCs remains a critical challenge for future technological applications. To tackle the inherent instability of SMA materials under the ambient conditions, much effort has been made to improve OSCs stability, including device modification and new materials design. Here we proposed a new electron acceptor design strategy and developed a “quasi-macromolecule”(QM) with an A-π-A structure,where the functionalized π-bridge is used as a linker between two SMAs(A), to improve the long-term stability without deteriorating device efficiencies. Such type of QMs enables excellent synthetic flexibility to modulate their optical/electrochemical properties, crystallization and aggregation behaviors by changing the A and π units. Moreover, QMs possess a unique long conjugated backbone combining high molecular weight over 3.5 k Da with high purity. Compared with the corresponding SMA BTP-4F-OD(Y6-OD), the devices based on newly synthesized A-π-A type acceptors QM1 and QM2 could exhibit better device stability and more promising PCEs of 17.05% and 16.36%, respectively. This kind of “molecular-framework”(A-π-A)structure provides a new design strategy for developing high-efficiency and-stability photovoltaic materials.
基金financial support from the National Natural Science Foundation of China (Nos. 21822503, 21534003, 21125420, 21603044 and 91427302)the Ministry of Science and Technology of China (Nos. 2016YFA0200704 and 2016YFF0203803)+1 种基金the Beijing Nova Program (No. Z17110001117062)the Youth Innovation Promotion Association CAS and the Chinese Academy of Sciences
文摘For bulk-heterojunction organic solar cells, the morphology of the blend films highly influence the exciton dissociation and charge transport process. In this work, two novel A-π-D-π-A(A represents the acceptor unit and D represents the donor unit) backbone structure small molecular electron donors based on two dimensional conjugated naphtho[1,2-b:5,6-b']dithiophene(NDT) with different end alkyl chains, named as NDT-3T-EH and NDT-3T-O, have been designed and synthesized. The photovoltaic property of NDT-3T-O-based device is better than that of the NDT-3T-EH and the best efficiency reaches 7.06%, and the photovoltaic property of NDT-3T-EH reaches 6.11%. The difference in the performance should be attributed to the different morphology and phase separation resulted from the different crystallinity and aggregation ability of two donors. The results demonstrate that the optimized end alkyl chains can be used to design A-π-D-π-A backbone structure small molecular electron donors for smallmolecule organic solar cells.
