Improved Performance for Inverted Organic Photovoltaics via Spacer between Benzodithiophene and Benzothiazole in Polymers

Lal Mohammad, Qiliang Chen, Abu Mitul, Jianyuan Sun, Devendra Khatiwada, Bjorn Vaagensmith, Cheng Zhang, Jing Li, Qiquan Qiao

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


In this work, the effects of the spacer between benzo[1,2-b;3,4-b′]dithiophene (BDT) and dialkoxybenzothiadiazole (ROBT) in polymers were investigated for applications in organic solar cells. Polymer PBDT-2T-ROBT has a bithiophene (2T) spacer between the BDT and ROBT units, whereas PBDT-ROBT is a direct copolymer of BDT and ROBT. The polymer/PC70BM solar cells using both polymers were fabricated and optimized via polymer/fullerene ratio, solvent, and solvent additives. The spacer has significantly improved solar cell performance from 1.28% (Voc =0.77 V, Jsc = 3.13 mA/cm2, FF = 53.11%) to 5.11% (Voc = 0.66 V, Jsc = 13.33 mA/cm2, FF = 58.12%). The X-ray diffraction (XRD) spectra show the PBDT-2T-ROBT/PC70BM blended film is semicrystalline, whereas the PBDT-ROBT/PC70BM film is amorphous. This indicates that the spacer facilitates polymer organization for higher carrier mobility in the film. Atomic force microscopy (AFM) topography and phase images show that PBDT-2T-ROBT/PC70BM films form fibrillar networks, whereas PBDT-ROBT/PC70BM films exhibit larger granular morphology. The photoinduced charge extraction by linearly increasing voltage (Photo-CELIV) measurements show that PBDT-2T-ROBT/PC70BM has a mobility of 9.59 × 10-5 cm2/(V·s), which is higher than the mobility of 8.64 × 10-5 cm2/(V·s) for PBDT-ROBT/PC70BM film.

Original languageEnglish (US)
Pages (from-to)18992-19000
Number of pages9
JournalJournal of Physical Chemistry C
Issue number33
StatePublished - Aug 20 2015
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • General Energy
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films


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