N,N-Di aryl anilinosquaraines and Their Application to Organic Photovoltaics

Siyi Wang, Lincoln Hall, Vyacheslav V. Diev, Ralf Haiges, Guodan Wei, Xin Xiao, Peter I. Djurovich, Stephen R. Forrest, Mark E. Thompson

Research output: Contribution to journalArticlepeer-review

106 Scopus citations

Abstract

We report new derivatives of symmetric squaraine dyes with N,N-diarylanilino substituents that have high solubility and high absorptivity (ε = 0.71-4.1 ×105 M-1cm-1) in the red solar spectral region (λmax = 645-694 nm) making them promising candidates for application in organic photovoltaics (OPVs). Unsymmetrical N,N-diisobutylanilino- and N,N-diphenylanilino(diphenylamino) squaraines have also been prepared that give blue-shifted absorption spectra (λmax = 529-535 nm) relative to their symmetric counterparts. Compared to bis(N,N-diisobutylanilino)squaraine, both symmetrical and unsymmetrical N,N-diarylanilino squaraines show markedly broader absorption bands in solution than their N,N-dialkylanilino squaraine counterparts: the full width at half-maximum (fwhm) for N,N-diarylanilino squaraines range from 1280-1980 cm-1, while the fwhm value for the N,N-diisobutylanilino squarine is only 630 cm-1. The absorption bands for thin films of N,N-diarylanilino squaraines broaden further to 2500-3300 cm-1. N,N-Diarylanilino squaraines are fluorescent, albeit with lower quantum yields than bis(N,N-diisobutylanilino)squaraine (φPL = 0.02-0.66 and 0.80, respectively). OPVs were prepared with solution processed squaraine layers using the following structure: ITO/squaraine (66-85 Å)/C60 (400 Å)/BCP (100 Å)/Al (1000 Å), BCP = bathocuproine. Devices using thin films of the bis(N,N-diarylanilino)squaraines as donor layers show improved performance relative to OPVs prepared with bis(N,N-dialkylanilino) squaraines, i.e. bis(N,N-diisobutylanilino)squaraine: open-circuit voltage Voc = 0.59 ± 0.05 V, short-circuit current Jsc = 5.58 ± 0.16 mA/cm2, fill factor FF = 0.56 ± 0.03, and power conversion efficiency η = 1.8 ± 0.2% under 1 sun, AM1.5G simulated illumination, compared with bis(N,N-diphenylanilino)squaraine: V oc = 0.82 ± 0.02 V, Jsc = 6.71 ± 0.10 mA/cm2, FF = 0.59 ± 0.01, and η = 3.2 ± 0.1%. Morphological studies of thin films suggest that the solubility of bis(N,N-diarylanilino)squaraines plays an important role in controlling the optoelectronic properties of the OPVs. © 2011 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)4789-4798
Number of pages10
JournalChemistry of Materials
Volume23
Issue number21
DOIs
StatePublished - Nov 8 2011
Externally publishedYes

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