The open-circuit voltage （Voc） of classical photovoltaic polymers, such as P3HT and PTB7-Th, are always restricted when combining with fullerene derivatives, due to the difficulty of modulating the energy levels of ...The open-circuit voltage （Voc） of classical photovoltaic polymers, such as P3HT and PTB7-Th, are always restricted when combining with fullerene derivatives, due to the difficulty of modulating the energy levels of fullerene derivatives. Thus, design of new non-fullerene small molecule acceptor （NFSMA） is very significant to match with these mature polymer donors and improve the Voc and power conversion efficiency （PCE）. Here, a new benzotriazole （BTA）-based NFSMA, BTA7 was synthesized by adopting A2----A1--D--A1--A2 type molecular backbone. By using a strong electron-accepting unit of malononitrile （M） as terminal segment A2, BTA7 demonstrates strong crystallinity, red-shifted absorption spectrum and down-shifted lowest unoccupied molecular orbital （LUMO） energy levels in comparison with BTA1 and BTA2. Organic solar cells （OSCs） based on PTB7-Th：BTA7 realized a high Voc of 1.05 V with a moderate PCE of 4.60%. The energy loss （Eloss = Eg - eVoc） of 0.53 eV is lower than the experiential minimum value of 0.6 eV, which indicates PTB7-Th still has large potential to improve the Voc and photovoltaic performance after the development of novel electron acceptors.展开更多
In-situ growth of CdS nanorods (NRs) has been demonstrated via solvothermal, in a low band gap polymer, poly [[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b’] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbony...In-situ growth of CdS nanorods (NRs) has been demonstrated via solvothermal, in a low band gap polymer, poly [[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b’] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophenediyl]] (PTB7). It is a high yielding, green approach as it removes use of volatile and hazardous chemicals such as pyridine as ligand which are conventionally used to synthesize precursors of CdS (NRs). Moreover the solvothermal process is a zero emission process being a close vessel synthesis and hence no material leaching into the atmosphere during the synthesis. The PTB7:CdS nanocomposite has been characterized by SEM, XRD, FTIR, UV-visible spectroscopy techniques. The photoluminescence (PL) spectroscopy study of PTB7 with CdS NRs has shown significant PL quenching by the incorporation of CdS NRs in PTB7;this shows that CdS NRs are efficient electron acceptors with the PTB7. The PTB7:CdS is used as active layer in the fabrication of hybrid solar cells (HSC) as donor-acceptor combination in the bulk heterojunction (BHJ) geometry. The HSCs fabricated using this active layer without any additional supporting fullerene based electron acceptor has given power conversion efficiency of above 1%.展开更多
Organic photovoltaic cells (OPVs) have been investigated for a long time, and practical realizations have been also in progress due to their high photovoltaic performance over 12%. In this study, we fabricated normal ...Organic photovoltaic cells (OPVs) have been investigated for a long time, and practical realizations have been also in progress due to their high photovoltaic performance over 12%. In this study, we fabricated normal OPVs and investigated the reason of an improved optical-to-electrical conversion efficiency by annealing the MoOx layer. The photoconversion efficiency was improved up to 5.65% from 2.05% after annealing at 160°C for 5 min, and the external quantum efficiency also increased for all the measurement wavelength ranging from 300 to 900 nm. Especially, the short circuit current density increased among photovoltaic parameters. The carrier transport resistance of photoactive layer was found to be reduced by evaluating the impedance measurement. These results indicate that defects at the MoOx/organic interface were successfully reduced by the thermal annealing process of MoOx layer. The efficient carrier transport was realized for the annealed-device, resulting in the high device performance. In addition, the relaxation and electron recombination times were also reduced by the annealing process, which lead to the improved photovoltaic performance.展开更多
Conjugated polymers are widely used in organic optoelectronic devices due to their solution processability, thermal stability and structural diversity. Generally, alkyl side chains must be utilized to increase the sol...Conjugated polymers are widely used in organic optoelectronic devices due to their solution processability, thermal stability and structural diversity. Generally, alkyl side chains must be utilized to increase the solubility of final polymers in the processing solvent. However, the effects of different type alkyl chains on the properties of n-type photovoltaic polymers have rarely been investigated. In this article, we synthesized three naphthodithiophene diimide（NDTI） based polymers containing bulky alkyl chains with different branching position, named as NDTI-1, NDTI-2 and NDTI-3, respectively. We systematically investigated the effect of different branching point on the molecular packing, charge transport and photovoltaic performance. When moving the branching point away from the backbone, the intermolecular interaction became stronger, which could be proved by 2D grazing incidence wide angle X-ray scattering（GIWAXS） measurement. Therefore, the electron mobilities in organic field-effect transistors gradually increased from 2.11×10-3 cm2 V/-1 s-1 for NDTI-1 to 4.70×10-2 cm2 V/-1 s-1 for NDTI-2 and 9.27×10-2 cm2 V/-1 s-1 for NDTI-3,which are quite high values for polymers with face-on orientation. In addition, the NDTI-2 and NDTI-3 thin films exhibited redshifted absorption spectra compared with NDTI-1. When blending with three classic donor polymers PBDB-T, PTB7-Th and PE61, NDTI-2 based devices always showed the higher power conversion efficiencies（PCEs） than the other two polymers（beside the comparable result of PTB7-Th:NDTI-3 combination） as a result of the high photocurrent response and high fill factor. Our results indicate that bulky alkyl chain with branching point at 2-position should be a good and safe choice for the design of naphthodithiophene diimide-based and even naphthalene diimide-based n-type photovoltaic polymers.展开更多
基金supported by the National Key Research and Development Program of China (2017YFA0206600)the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (QYZDB-SSW-SLH033)+1 种基金the National Natural Science Foundation of China (51673048, 51473040 and 21602040)the Natural Science Foundation of Beijing (2162045)
文摘The open-circuit voltage （Voc） of classical photovoltaic polymers, such as P3HT and PTB7-Th, are always restricted when combining with fullerene derivatives, due to the difficulty of modulating the energy levels of fullerene derivatives. Thus, design of new non-fullerene small molecule acceptor （NFSMA） is very significant to match with these mature polymer donors and improve the Voc and power conversion efficiency （PCE）. Here, a new benzotriazole （BTA）-based NFSMA, BTA7 was synthesized by adopting A2----A1--D--A1--A2 type molecular backbone. By using a strong electron-accepting unit of malononitrile （M） as terminal segment A2, BTA7 demonstrates strong crystallinity, red-shifted absorption spectrum and down-shifted lowest unoccupied molecular orbital （LUMO） energy levels in comparison with BTA1 and BTA2. Organic solar cells （OSCs） based on PTB7-Th：BTA7 realized a high Voc of 1.05 V with a moderate PCE of 4.60%. The energy loss （Eloss = Eg - eVoc） of 0.53 eV is lower than the experiential minimum value of 0.6 eV, which indicates PTB7-Th still has large potential to improve the Voc and photovoltaic performance after the development of novel electron acceptors.
文摘In-situ growth of CdS nanorods (NRs) has been demonstrated via solvothermal, in a low band gap polymer, poly [[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b’] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophenediyl]] (PTB7). It is a high yielding, green approach as it removes use of volatile and hazardous chemicals such as pyridine as ligand which are conventionally used to synthesize precursors of CdS (NRs). Moreover the solvothermal process is a zero emission process being a close vessel synthesis and hence no material leaching into the atmosphere during the synthesis. The PTB7:CdS nanocomposite has been characterized by SEM, XRD, FTIR, UV-visible spectroscopy techniques. The photoluminescence (PL) spectroscopy study of PTB7 with CdS NRs has shown significant PL quenching by the incorporation of CdS NRs in PTB7;this shows that CdS NRs are efficient electron acceptors with the PTB7. The PTB7:CdS is used as active layer in the fabrication of hybrid solar cells (HSC) as donor-acceptor combination in the bulk heterojunction (BHJ) geometry. The HSCs fabricated using this active layer without any additional supporting fullerene based electron acceptor has given power conversion efficiency of above 1%.
文摘Organic photovoltaic cells (OPVs) have been investigated for a long time, and practical realizations have been also in progress due to their high photovoltaic performance over 12%. In this study, we fabricated normal OPVs and investigated the reason of an improved optical-to-electrical conversion efficiency by annealing the MoOx layer. The photoconversion efficiency was improved up to 5.65% from 2.05% after annealing at 160°C for 5 min, and the external quantum efficiency also increased for all the measurement wavelength ranging from 300 to 900 nm. Especially, the short circuit current density increased among photovoltaic parameters. The carrier transport resistance of photoactive layer was found to be reduced by evaluating the impedance measurement. These results indicate that defects at the MoOx/organic interface were successfully reduced by the thermal annealing process of MoOx layer. The efficient carrier transport was realized for the annealed-device, resulting in the high device performance. In addition, the relaxation and electron recombination times were also reduced by the annealing process, which lead to the improved photovoltaic performance.
基金supported by the National Key Research and Development Program of China (2017YFA0206600)the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (QYZDB-SSW-SLH033)the National Natural Science Foundation of China (51673048, 21875052)
文摘Conjugated polymers are widely used in organic optoelectronic devices due to their solution processability, thermal stability and structural diversity. Generally, alkyl side chains must be utilized to increase the solubility of final polymers in the processing solvent. However, the effects of different type alkyl chains on the properties of n-type photovoltaic polymers have rarely been investigated. In this article, we synthesized three naphthodithiophene diimide（NDTI） based polymers containing bulky alkyl chains with different branching position, named as NDTI-1, NDTI-2 and NDTI-3, respectively. We systematically investigated the effect of different branching point on the molecular packing, charge transport and photovoltaic performance. When moving the branching point away from the backbone, the intermolecular interaction became stronger, which could be proved by 2D grazing incidence wide angle X-ray scattering（GIWAXS） measurement. Therefore, the electron mobilities in organic field-effect transistors gradually increased from 2.11×10-3 cm2 V/-1 s-1 for NDTI-1 to 4.70×10-2 cm2 V/-1 s-1 for NDTI-2 and 9.27×10-2 cm2 V/-1 s-1 for NDTI-3,which are quite high values for polymers with face-on orientation. In addition, the NDTI-2 and NDTI-3 thin films exhibited redshifted absorption spectra compared with NDTI-1. When blending with three classic donor polymers PBDB-T, PTB7-Th and PE61, NDTI-2 based devices always showed the higher power conversion efficiencies（PCEs） than the other two polymers（beside the comparable result of PTB7-Th:NDTI-3 combination） as a result of the high photocurrent response and high fill factor. Our results indicate that bulky alkyl chain with branching point at 2-position should be a good and safe choice for the design of naphthodithiophene diimide-based and even naphthalene diimide-based n-type photovoltaic polymers.
