Synergistic Effect of Fluorination on Molecular Energy Level Modulation in Highly Efficient Photovoltaic Polymers

Abstract

The synergistic effect of fluorination on molecular energy level modulation is realized by introducing fluorine atoms onto both the donor and the acceptor moieties in a D-A polymer, and as a result, the polymer solar cell device based on the trifluorinated polymer, PBT-3F, shows a high efficiency of 8.6%, under illumination of AM 1.5G, 100 mW cm(-) (2) .

Impact of Backbone Fluorination on π-Conjugated Polymers in Organic Photovoltaic Devices: A Review

“…It is interesting to note that, unlike the previous reports by Yu et al [53] discussed above, the optical band-gap is slightly increased upon backbone fluorination. A similar behavior has also been reported by other groups [27,57,58], demonstrating that the addition of a withdrawing fluorine atom may have more influence on the HOMO level than on the LUMO level. This result is somewhat surprising, as it is generally believed that the HOMO level of a D/A copolymer should be mostly controlled by the fluorine-free electron-donor moiety [6].…”

Organic Photovoltaics Based on Poly(3,4-phenylenedioxy-2,5-thienylenevinylene)s

“…The lower HOMO energy of PPhDOTFV compared to PPhDOTV originates from the strongly accepting nature of fluorine in the phenylene part of PPhDOTFV, which is beneficial for obtaining a higher V oc in BHJ OPVs. [19][20][21] The energy levels of the lowest unoccupied molecular orbital (LUMO) of PPhDOTV and PPhDOTFV estimated from their E g values and HOMO levels were situated at ¹3.48 and ¹3.68 eV, respectively.…”

Balancing High Open Circuit Voltage over 1.0 V and High Short Circuit Current in Benzodithiophene‐Based Polymer Solar Cells with Low Energy Loss: A Synergistic Effect of Fluorination and Alkylthiolation

“…As the three synthetic steps illustrated in Scheme 1, such a synthetic route avoided the synthetically unfavored trimethylsilyl (TMS) protection and deprotection procedure, appearing more sound when comparing to the synthesis of similar mono mer (fluorinated alkylthieonyl BDT) by Hou and co-workers [10] The resulted key monomer M1 (BDTT-SF) was fully characterized by 1 H NMR, 13 C NMR, and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). To obtain the target polymer PBDTT-SF-TT and PBDTT-SF-BDD, the polymerization was carried out by a Pd(PPh 3 ) 4 (PDI) of 2.53 for PBDTT-SF-TT and M n of 33 400 Da with a PDI of 3.92 for PBDTTT-SF-BDD, respectively.…”

“…To date, only one polymer PBDT-PQD2 [8] and other three polymers PBDT-PQD1, PBDT-PQD3, [8] and PDST-TT are found in E Loss level below or close to 0.6 eV (the dash line in Figure 1a), while their low PCEs have been totally out from the scope of state-of-the-art OPV development. Meanwhile, prior to the fill factor (FF), coordinately high V oc and J sc should be expected; however, in BDT-polymer/ fullerene solar cells as illustrated in Figure 1b, the gain of large J sc and high V oc are in fact contradictory: for polymer/PC 71 BM cells, only one of the polymers, PDST-TT [9] attains a V oc > 0.90 V, while its J sc only remains at 10.15 mA cm −2 ; for other polymers (e.g., PBT-3F, [10] PBDT-TS1, [11] PBDT-TSR [12] ) whose J sc s are higher than 14.00 mA cm −2 , their V oc all fall below 0.86 V, few of them stay in between 0.80 and 0.86 V, even though their PCE could have reached high values as 8.6%, 9.48%, and 10.20%.…”

“…Second, relying on its small van der Waals radius and high electronegativity (3.98 on the Pauling scale), [18] fluorine (F) atom favors F-π, F-H, and F-S [19] inter-and intramolecular interactions and therefore fluorination would simultaneously increase both the electron affinity (EA) and ionization potential (IP) of the conjugated polymers with a deepening of both LUMO and HOMO without significantly affecting the E g . [20][21][22][23][24] Nevertheless, despite that most of these work focused on fluorination on the acceptor moiety (TT-ester, for example) in the D-A polymers, Yu and co-workers and Hou and co-workers systematically studied the multifluorination on both D and A moieties and proved that introduction of F atom(s) into various positions at alkyl-, alkylthieonyl-BDT, and TT motifs (PTBFx series [20] and PBT-xF [10] (x: 0-3)) led to distinct influences on their PV performance. For the former, HOMO level had been systematically lowered from −4.94 eV for PTBF0 to −5.48 eV for PTBF3; for the latter, they started deepening HOMO from −4.73 eV for PBT-0F to −4.90 eV for PBT-3F, corresponding to the voltage elevation from 0.58 to 0.75 V and from 0.56 to 0.78 V, respectively.…”