Syntheses of pyrimidine‐based polymers containing electron‐withdrawing substituent with high open circuit voltage and applications for polymer solar cells

Abstract

Polymers using new electron-deficient units, 2-pyriminecarbonitrile and 2-fluoropyrimidine, were synthesized and utilized for the photovoltaics. Donor-acceptor (D-A) types of conjugated polymers (PBDTCN, PBDTTCN, PBDTF, andas electron rich unit and 2-pyriminecarbonitrile or 2-fluoropyrimidine as electron deficient unit were synthesized. We designed pyrimidine derivatives in which strong electron-withdrawing group (CBN or fluorine) was introduced to the C2 position for the generation of strong electron-deficient property. By the combination with the electron-rich unit, the pyrimidines will provide low band gap polymers with low highest occupied molecular orbital (HOMO) energy levels for higher open-circuit voltages (V OC ). For the syntheses of the polymers, the electron-rich and the electrondeficient units were combined by Stille coupling reaction with Pd(0)-catalyst. Absorption spectra of the thin films of PBDTTCN and PBDTTF with BDTT unit show shift to a longer wavelength region than PBDTCN and PBDTF with BDT unit. Four synthesized polymers provided low electrochemical bandgaps of 1.56 to 1.96 eV and deep HOMO energy levels between 25.67 and 25.14 eV.

Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

“…In 2012, based on the main chain BDT-TR-CED-TR, Yang and co-workers first reported PBDTTST (2012) by further introducing side chains hexyl and 3-(methoxymethyl) heptane into the cyclobut-3-ene-1,2-dione (CED) and BDT units in turn. [119] Afterward, PBDTCN (2016) ,PBDTF (2016) , PBDTTCN (2016) and PBDTTF (2016) were synthesized by Kim et al; [259] PBDT-ODZ (2018) was also prepared by Xu et al [260] Notably, PBDT-ODz: ITIC-Th based OSC achieves a promising V oc of 1.06 V,J sc of 17.10 mA/cm 2 , FF of 68.1% and PCE of 12.07%. Compared with the acceptor units CED and pyrimidine (PMD), 1,3,4oxadiazole (ODz) presented a more ideal electron-withdrawing, which effectively promotes the hole/electron mobility in polymer backbone.…”