Synthesis and Photovoltaic Performance of a [1,2,3]Triazolo[4,5‐g]quinoxaline‐Based Low‐Bandgap Polymer

Abstract

A narrow-bandgap conjugated polymer, PFDTBTzQ-2OC1, is prepared by alternating [1,2,3] triazolo [4,5-g]quinoxaline and 9,9-didodecyl-fl uorene. With a bandgap of 1.63 eV, this polymer has wide absorption ranging from 300-760 nm in fi lm. Bulk heterojunction solar cells fabricated by blending PFDTBTzQ-2OC1 with [6,6]-phenyl-C 71 -butyric acid methyl ester exhibit a maximum power conversion effi ciency of 1.31%, with a short-circuit current density of 1.98 mA cm -2 , an open-circuit voltage of 0.74 V, and a fi ll factor of 0.47. as the power conversion effi ciency (PCE) of PSCs has been improved from 1% to over 8%, [8][9][10] with a recent record hitting 9.2%. [ 11 ] However, there are still some key issues that need to be addressed to push PSCs for commercial application which include new materials and device engineering development to push the PCE up to 10%, reliable encapsulation technology to secure long-life workable devices, and robust mass-production processes for device making. [1][2][3][4][5][6] The development of novel low-bandgap polymers with suitable energy levels, high charge carrier mobility, and broad absorption for solar light is the mainstream of polymer research for high-performance PSCs. Last but not least, the polymers should have good solubility tailoring for solution processing. The popular design of low-bandgap polymers adopt a so-called D-A copolymer strategy by alternating electron-rich (D) and electrondefi cient (A) units along the conjugated backbone. Among them, many developed D-A copolymers have demonstrated promising photovoltaic performances, with PCEs higher than 6%. [ 2,[12][13][14][15][16][17] Besides bandgap control, the regulation of molecular energy levels (the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)) of conjugated polymers is also crucial for D-A polymer design. Electron donating or accepting units of different strength have been used in molecular design for this purpose. [ 18 ] A nice correlation study of the acceptor strength with low-bandgap polymers was addressed by Kose and coworkers. [ 19 ]

Effect of carbon hybridization in 9H-fluorene unit on the photovoltaic properties of different fluorene-based conjugated polymers

“…The characteristics are summarized in Table 1. Similar to the TzQx-based polymers, these substituted 9H-fluorene-based polymers exhibit two major absorption bands, 23,24,28,29 in which simple benzotriazole-based polymers only show one broad absorption band. 30 –32 The weak absorption at shorter wavelength is attributed to the π–π* transitions of the conjugated main chain and the strong absorption at the longer wavelength is owed to the intermolecular charge transfer interaction between the substituted 9H-fluorene donating unit and TzQx accepting unit.…”

Benzothiadiazole Versus Thiophene: Influence of the Auxiliary Acceptor on the Photovoltaic Properties of Donor–Acceptor‐Based Copolymers

“…As shown in Scheme , compound 1 – 3 were synthesized according to the literature . The T1 unit (compound 6 ) was synthesized via a cyclization reaction .…”

Synthesis and properties of mono‐ and di‐fluoro‐substituted 2,3‐didodecylquinoxaline‐based polymers for polymer solar cells

“…An attempt to tune the properties of Qx‐based polymers, various electron‐rich units such as benzodithiophene (BDT), indacenodithiophene, fluorene, carbazole, and thiophene derivatives were polymerized with Qx derivatives . Also, a variety of electron withdrawing units such as fluoro, imide, thiadiazole, and triazole were attached on the 6 and 7th‐positions of the Qx backbone. The careful study suggests that the electron‐rich BDT and tri‐thiophene (Tt) derivatives are the best choices for the preparation of efficient Qx‐based donor–acceptor (D–A) polymers.…”

“…Worth to note that the aryl substituents were incorporated mostly on 2nd and 3rd‐positions of the Qx unit (Fig. for example) and polymerized with many different electron rich units, and explored as a donor material on PSCs . The efficient aryl‐substituted 6,7‐difluoroquinoxaline‐based polymers containing electron rich BDT (PBDT‐TFQ and PDBTQEH) and Tt (PDFQx‐3 T) are outlined in Figure .…”

“…) was also found to be very high . Consequently, we think that the polymerization of Tt derivative with each of FQx and DFQx derivatives might give efficient polymer for PSCs because the small structural changes on the polymer main or side chains bring the big difference in their photovoltaic performance . We inserted alkyl (n‐hexyl) group on the 4 + position of thiophene attached to Qx unit (Fig.…”