Jeramy D. Zimmerman
University of Michigan
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Featured researches published by Jeramy D. Zimmerman.
Nano Letters | 2009
Michael S. Arnold; Jeramy D. Zimmerman; Christopher Kyle Renshaw; Xin Xu; Richard R. Lunt; Christine M. Austin; Stephen R. Forrest
We demonstrate that photogenerated excitons in semiconducting carbon nanotubes (CNTs) can be efficiently dissociated by forming a planar heterojunction between CNTs wrapped in semiconducting polymers and the electron acceptor, C(60). Illumination of the CNTs at their near-infrared optical band gap results in the generation of a short-circuit photocurrent with peak external and internal quantum efficiencies of 2.3% and 44%, respectively. Using soft CNT-hybrid materials systems combining semiconducting small molecules and polymers, we have fabricated broad-band photodetectors with a specific detectivity >10(10) cm Hz(1/2) W(1-) from lambda = 400 to 1450 nm and a response time of tau = 7.2 +/- 0.2 ns.
Advanced Materials | 2012
Xin Xiao; Guodan Wei; Siyi Wang; Jeramy D. Zimmerman; Christopher Kyle Renshaw; Mark E. Thompson; Stephen R. Forrest
Two squaraine (SQ) donor molecules with different absorption bands are blended together for better coverage of the solar spectrum. The blend SQ device shows a significant improvement compared with single SQ donor devices. By applying a solvent annealing process and a compound buffer layer, a power-conversion efficiency of 5.9 ± 0.3% is achieved under 1 sun illumination.
Nano Letters | 2012
Jeramy D. Zimmerman; Xin Xiao; Christopher Kyle Renshaw; Siyi Wang; Vyacheslav V. Diev; Mark E. Thompson; Stephen R. Forrest
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.
Advanced Materials | 2010
Jeramy D. Zimmerman; Vyacheslav V. Diev; Kenneth Hanson; Richard R. Lunt; Eric Kai Hsiang Yu; Mark E. Thompson; Stephen R. Forrest
/1 0 4 While few examples have been demonstrated, near-infrared (NIR) organic photodetectors with response at wavelengths ( λ ) beyond the cutoff of Si (i.e., λ > 1100 nm) are interesting for use in imaging and other detection applications. [ 1 ] In previous work, polymer photodetectors with response at λ > 1000 nm have been demonstrated, but the optical sensitivity is generally due to a long absorption tail having an external quantum effi ciency (EQE) less than a few percent. [ 2 – 4 ] Organic materials systems with a large NIR photoresponse are rare for several reasons. A type-II (staggered) heterojunction must be formed between the donor and acceptor materials with a suffi cient energy offset to dissociate photogenerated excitons; as the energy gap is decreased, fi nding molecular combinations with suitable energy alignments becomes increasingly diffi cult. In addition, exciton lifetimes generally decrease with energy gap due to exciton–phononinduced recombination (i.e., internal conversion). [ 5 , 6 ] These diffi culties have motivated the development of hybrid organic– inorganic devices using polymeric and small-molecule materials in conjunction with II–VI quantum dots (with EQE <1% at λ > 1000 nm) [ 7 ] or single-walled carbon nanotubes (EQE ≈ 2% at λ = 1150 and 1300 nm). [ 8 ] Here, we demonstrate an NIR EQE = 6.5% at λ = 1350 nm using photodetectors based on triply linked porphyrin-tape dimers. These porphyrin tapes are representative of a promising new class of materials that can be modifi ed to exhibit even longer wavelength response by spatially extending the conjugation of the π-electron system. [ 5 ]
Applied Physics Letters | 2013
Xin Xiao; Jeramy D. Zimmerman; Brian E. Lassiter; Kevin J. Bergemann; Stephen R. Forrest
We describe a hybrid planar-mixed heterojunction (PM-HJ) organic photovoltaic cell based on tetraphenyldibenzoperiflanthene (DBP) and C70 with a power conversion efficiency of up to 6.4% ± 0.3%. Optimized cells consist of a DBP:C70 mixed layer at a volume ratio of 1:8 and a 9-nm thick C70 cap layer. The external quantum efficiency (EQE) in the visible of the PM-HJ cell is up to 10% larger than the mixed-HJ cell that lacks a C70 acceptor cap layer. The improvement in EQE is attributed to reduced exciton quenching at the MoO3 anode buffer layer surface. This leads to an internal quantum efficiency >90% between the wavelengths of λ = 450 nm and 550 nm, suggesting efficient exciton dissociation and carrier extraction in the PM-HJ cell. The power conversion efficiency under simulated AM 1.5G, 1 sun irradiation increases from 5.7% ± 0.2% for the mixed-HJ cell to 6.4% ± 0.3% for the PM-HJ cell, with a short-current density of 12.3 ± 0.3 mA/cm2, open circuit voltage of 0.91 ± 0.01 V, and fill factor of 0.56 ± 0.01.
Angewandte Chemie | 2010
Vyacheslav V. Diev; Kenneth Hanson; Jeramy D. Zimmerman; Stephen R. Forrest; Mark E. Thompson
Porphyrins have been explored for a number of potential optoelectronic applications that require strong absorption in the near-infrared (NIR) spectral region; these applications include organic electronics, nonlinear optics, and telecommunication technologies. Porphyrins have also been investigated as active materials in photovoltaic cells because of their high efficiency of charge separation and transport, strong absorbance in the visible region, high chemical stability, and the ease with which their optoelectronic properties can be tuned with chemical modification. The absorption bands of porphyrins are not readily shifted into the deepred and NIR spectral regions, and also tend to be narrow, thus minimizing their overlap with the solar spectrum. Triply bridged, (b,meso,b), porphyrin tapes (Figure 1a, n= 0–22) show marked red-shifts in the porphyrin absorption bands, which extend deep into the NIR region. Triply fused porphyrins with n= 1,2 give absorbance in the mid-NIR region (i.e., conventional wavelengths for telecommunications, ca. 1.5 mm), however, these porphyrins are difficult to synthesize, have low solubility, and are isolated only in small quantities. Triply connected porphyrin dimers (Figure 1a, n= 0) have a strong absorbance at l= 1050 nm, are photoand chemically stable, have a high solubility, and can be easily prepared from monoporphyrins. Development of new organic dyes based on these accessible porphyrin dimers with absorption at the wavelengths for telecommunications (l= 1.5 mm) still remains a challenge. Extending the size of p conjugation in porphyrin systems results in most cases in a bathochromic (red) shift of the absorption. The conjugation of porphyrin dimers can be extended through several modes of substitution involving the meso, (b,b), (b,meso) and (b,meso,b) positions. For diporphyrins substituted with two alkyne groups at the terminal meso positions, the Q band is red-shifted by 130 nm (l= 1181 nm) relative to the parent dimer. In contrast, extending the conjugation in porphyrin dimers by benzannulating b,bpyrrolic positions red-shifts the Q band by only 18 nm, and the resulting compounds have poor solubility. Recently, it has been shown that anthracene rings can be fused to porphyrin dimers through the (b,meso,b) mode, which leads to a red-shift of the Q band to 1495 nm. However, the anthracene-fused diporphyrin exhibits the same undesirable difficulties found with higher porphyrin tapes, for example, synthetic difficulty, low yields and low solubility. Moreover, fusion of anthracene rings is limited only to alkoxy-substituted derivatives. The effects of aromatic ring fusion to porphyrin tapes in a (meso,b) mode have not been explored. We have analyzed the structures of the diporphyin core (Figure 1b), a (b,meso,b) triply fused aromatic system (Figure 1c), and a (b,meso) doubly fused molecule (Figure 1d) using standard DFT methods. Significant bathochromic shifts of the lowestenergy transition are expected in all cases. Unlike the case of anthracene-fused porphyrins and porphyrin tapes, in which the planarity causes aggregation and low solubility, the pyrene–(b,meso)-fused diporphyrin displays out-of-plane distortion that is known to improve solubility and processibility in conjugated aromatics. By taking into account the predicted bathochromic shift, distortion from planarity, and ease of synthesis, the (b,meso)-fused pyrene diporphyrin from Figure 1. a) General structure of triply fused porphyrins. b)–d) Structures of diporphyrin hybrids calculated at B3LYP/6-31G with calculated red-shifts of the lowest-energy transitions compared to the parent diporphyrin.
Applied Physics Letters | 2012
Brian E. Lassiter; Jeramy D. Zimmerman; Anurag Panda; Xin Xiao; Stephen R. Forrest
We demonstrate a tandem organic photovoltaic cell incorporating solution- and vacuum-deposited small molecules as the active layers. A blue and green-absorbing boron subphthalocyanine chloride:C70 graded heterojunction (HJ) sub-cell is combined with a green and red-absorbing functionalized squaraine/C70 bilayer HJ sub-cell, resulting in a tandem cell with a wavelength response from 350 nm to 800 nm. The efficiency of the cells depends on process conditions such as solvent annealing, resulting in nanocrystalline morphology that leads to improved charge and exciton transport compared with un-annealed cells. The incorporation of C70 in both sub-cells leads to an increase of short-circuit current by at least 30% compared to analogous cells using C60. The optimized power conversion efficiency of the tandem cell is 6.6% ± 0.1%, with an open-circuit voltage of 1.97 ± 0.1 V under simulated 1 sun, AM 1.5G illumination. The tandem cell voltage is equal to the sum of the constituent sub-cells, indicating that the tr...
Applied Physics Letters | 2008
Uttam Singisetti; Mark A. Wistey; Jeramy D. Zimmerman; Brian Thibeault; Mark J. W. Rodwell; A. C. Gossard; Seth R. Bank
We report a sharp reduction in the resistivity of Ohmic contacts using in situ deposition of molybdenum (Mo) contacts onto n-type In0.53Ga0.47As grown on InP. The contacts were formed by evaporating Mo onto the wafer using an electron beam evaporator connected to a molecular beam epitaxy chamber under ultrahigh vacuum. Transmission line measurements showed specific contact resistivities of 0.5±0.3 Ω μm2 (2.90 Ω μm), 0.9±0.4 Ω μm2 (4.3 Ω μm), and 1.3±0.4 Ω μm2 (4.7 Ω μm) for Mo on abrupt InAs/InGaAs heterojunctions, graded InAs/InGaAs, and InGaAs films, respectively. These low resistances meet the requirements for terahertz transistors.
Journal of Organic Chemistry | 2012
Vyacheslav V. Diev; Cody W. Schlenker; Kenneth Hanson; Qiwen Zhong; Jeramy D. Zimmerman; Stephen R. Forrest; Mark E. Thompson
A systematic study of the preparation of porphyrins with extended conjugation by meso,β-fusion with polycyclic aromatic hydrocarbons (PAHs) is reported. The meso-positions of 5,15-unsubstituted porphyrins were readily functionalized with PAHs. Ring fusion using standard Scholl reaction conditions (FeCl(3), dichloromethane) occurs for perylene-substituted porphyrins to give a porphyrin β,meso annulated with perylene rings (0.7:1 ratio of syn and anti isomers). The naphthalene, pyrene, and coronene derivatives do not react under Scholl conditions but are fused using thermal cyclodehydrogenation at high temperatures, giving mixtures of syn and anti isomers of the meso,β-fused porphyrins. For pyrenyl-substituted porphyrins, a thermal method gives synthetically acceptable yields (>30%). Absorption spectra of the fused porphyrins undergo a progressive bathochromic shift in a series of naphthyl (λ(max) = 730 nm), coronenyl (λ(max) = 780 nm), pyrenyl (λ(max) = 815 nm), and perylenyl (λ(max) = 900 nm) annulated porphyrins. Despite being conjugated with unsubstituted fused PAHs, the β,meso-fused porphyrins are more soluble and processable than the parent nonfused precursors. Pyrenyl-fused porphyrins exhibit strong fluorescence in the near-infrared (NIR) spectral region, with a progressive improvement in luminescent efficiency (up to 13% with λ(max) = 829 nm) with increasing degree of fusion. Fused pyrenyl-porphyrins have been used as broadband absorption donor materials in photovoltaic cells, leading to devices that show comparatively high photovoltaic efficiencies.
Applied Physics Letters | 2005
Dmitri O. Klenov; Joshua M. O. Zide; Jeramy D. Zimmerman; A. C. Gossard; Susanne Stemmer
High-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy was used to determine the atomic structure of interfaces between epitaxial ErAs layers with the cubic rock salt structure and In0.53Ga0.47As and GaAs, respectively. All layers were grown by molecular-beam epitaxy. We show that the interfacial atomic arrangement corresponds to the so-called chain model, in which the zinc blende semiconductor is terminated with a Ga layer. Image analysis was used to quantify the expansion between the first ErAs plane and the terminating Ga plane. In the HAADF images, a high intensity transfer from the heavy Er columns into the background was observed in the ErAs layer, whereas the background in In0.53Ga0.47As was of much lower intensity.