A series of seven dipyrrin-based bis-cyclometalated Ir(III) complexes have been synthesized and characterized. All complexes display a single, irreversible oxidation wave and at least one reversible reduction wave. The electrochemical properties were found to be dominated by dipyrrin centered processes. The complexes were found to display room temperature luminescence with emission maxima ranging from 658 to 685 nm. Through systematic variation of the cyclometalating ligand and the meso substituent of the dipyrrin moiety, it was found that the observed room temperature emission was due to phosphorescence from a dipyrrin-centered triplet state with quantum efficiencies up to 11.5%. Bis-cyclometalated Ir(III) dipyrrin based organic light emitting diodes (OLEDs) display emission at 682 nm with maximum external quantum efficiencies up to 1.0%.

We demonstrate that solvent vapor annealing of small molecular weight organic heterojunctions can be used to independently control the interface and bulk thin-film morphologies, thereby modifying charge transport and exciton dissociation in these structures. As an example, we anneal diphenyl-functionalized squaraine (DPSQ)/C(60) heterojunctions before or after the deposition of C(60). Solvent vapor annealing of DPSQ before C(60) deposition results in molecular order at the heterointerface. Organic photovoltaics based on this process have reduced open circuit voltages and power conversion efficiencies relative to as-cast devices. In contrast, annealing following C(60) deposition locks in interface disorder found in unannealed junctions while improving order in the thin-film bulk. This results in an increase in short circuit current by >30% while maintaining the open circuit voltage of the as-cast heterojunction device. These results are analyzed in terms of recombination dynamics at excitonic heterojunctions and demonstrate that the optimal organic photovoltaic morphology is characterized by interfacial disorder to minimize polaron-pair recombination, while improved crystallinity in the bulk increases exciton and charge transport efficiency in the active region.

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–1 cm–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 V oc = 0.59 ± 0.05 V, short-circuit current J sc = 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, J sc = 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.

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Squaraine (SQ) dyes are notable for their exceptionally high absorption coefficients extending from the green to the near-infrared. In this work, we utilize the functionalized SQ donor: 2,4-bis [4-(N-phenyl-1-naphthylamino)-2,6-dihydroxyphenyl] squaraine (1-NPSQ) by substitution of isobutylamines in the common "parent SQ" with arylamines to improve stacking and hence exciton and charge transport. The strong electron-withdrawing arylamine group results in a highest occupied molecular orbital energy of 5.3 eV, compared to 5.1 eV for the parent SQ, making 1-NPSQ a suitable donor when used with a C(60) acceptor in an organic photovoltaic cell. Optimized and thermally annealed, nanocrystalline heterojunction 1-NPSQ/C(60)/bathocuproine solar cells with an open circuit voltage of 0.90 ± 0.01 V, fill factor of 0.64 ± 0.01, and short circuit current of 10.0 ± 1.1 mA/cm(2) at 1 sun, AM1.5G illumination (solar spectrally corrected) result in a power conversion efficiency of 5.7 ± 0.6%. Crystallograpnic data suggest that the intermolecular stacking of 1-NPSQ molecules is closer than that of the parent SQ, thereby reducing the device series resistance and increasing its fill factor.