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Title: High open-circuit voltage small-molecule p-DTS(FBTTh 2 )2.ICBA bulk heterojunction solar cells – morphology, excited-state dynamics, and photovoltaic performance

The photovoltaic performance of bulk heterojunction solar cells using the solution-processable small molecule donor 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophene]-5-yl)benzo[c][1,2,5]thiadiazole) (p-DTS(FBTTh2)2 in combination with indene-C60 bis-adduct (ICBA) as an acceptor is systematically optimized by altering the processing conditions. A high open-circuit voltage of 1 V, more than 0.2 V higher than that of a p-DTS(FBTTh2)2:PC70BM blend, is achieved. However, the power conversion efficiency remains around 5% and thus is lower than ~8% previously reported for p-DTS(FBTTh2)2:PC70BM. Transient absorption (TA) pump–probe spectroscopy over a wide spectral (Vis-NIR) and dynamic (fs to μs) range in combination with multivariate curve resolution analysis of the TA data reveals that generation of free charges is more efficient in the blend with PC70BM as an acceptor. In contrast, blends with ICBA create more coulombically bound interfacial charge transfer (CT) states, which recombine on the sub-nanosecond timescale by geminate recombination. Furthermore, the ns to μs charge carrier dynamics in p-DTS(FBTTh2)2:ICBA blends are only weakly intensity dependent implying a significant contribution of recombination from long-lived CT states and trapped charges, while those in p-DTS(FBTTh2)2:PC70BM decay via an intensity-dependent recombination mechanism indicating that spatially separated (free) charge carriers are observed, which can be extracted as photocurrent from the device.
 [1] ;  [2] ;  [1] ;  [3] ;  [3] ;  [4] ;  [3]
  1. Agency for Science Technology and Research (A*STAR) (Singapore). Inst. of Materials Research and Engineering (IMRE).
  2. Max Planck Inst. for Polymer Research, Mainz (Germany)
  3. Univ. of California at Santa Barbara, Santa Barbara, CA (United States). Center for Polymers and Organic Solids.
  4. Max Planck Inst. for Polymer Research, Mainz (Germany)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Materials Chemistry. A
Additional Journal Information:
Journal Volume: 3; Journal Issue: 4; Journal ID: ISSN 2050-7488
Royal Society of Chemistry
Research Org:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States