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

Aung Ko Ko Kyaw, Dominik Gehrig, Jie Zhang, Ye Huang, Guillermo C. Bazan, Frederic Laquai*, Thuc Quyen Nguyen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

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(FBTTh 2 ) 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(FBTTh 2 ) 2 :PC 70 BM blend, is achieved. However, the power conversion efficiency remains around 5% and thus is lower than ∼8% previously reported for p-DTS(FBTTh 2 ) 2 :PC 70 BM. 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 PC 70 BM 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(FBTTh 2 ) 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(FBTTh 2 ) 2 :PC 70 BM 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. This journal is

Original languageEnglish (US)
Pages (from-to)1530-1539
Number of pages10
JournalJournal of Materials Chemistry A
Volume3
Issue number4
DOIs
StatePublished - Jan 28 2015

ASJC Scopus subject areas

  • Chemistry(all)
  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

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