The density of states in thin film copper phthalocyanine measured by Kelvin probe force microscopy

Çelebi, Kemal; Jadhav, Priya; Milaninia, Kaveh M.; Bora, Mayuri; Baldo, Marc A.

doi:10.1063/1.2976634

Cited by 40 publications

(39 citation statements)

References 13 publications

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“…This description is similar to the mobility edge picture developed for amorphous inorganic semiconductors, especially hydrogenated amorphous silicon, in which the mobility edge separates extended states from the localised ones. The distribution of traps below the transport level could be described by an exponential region [39]. In analogy to inorganic semiconductors, this exponential region of the DOS can be assumed to be a band tail of localised states induced by structural disorder.…”

Section: Resultsmentioning

confidence: 99%

Influence of the density of states on the open-circuit voltage in small-molecule solar cells

Galindo

Ahmadpour

Gerling

et al. 2014

Organic Electronics

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Section: Resultsmentioning

confidence: 99%

Influence of the density of states on the open-circuit voltage in small-molecule solar cells

Galindo

Ahmadpour

Gerling

et al. 2014

Organic Electronics

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“…[ 19 ] Increased order at the donor-acceptor interface could also lead to a change in the density of states for holes and electrons, so that disorderinduced gap tail states are reduced, increasing the electron quasi-Fermi level and decreasing the hole qausi-Fermi level, increasing V OC . [ 13b , 20 ] This hypothesis seems to fi t the observed losses in the open-circuit voltages, as the changes in V loss are within the range expected for disorder-induced gap tail states (0.1-0.2 eV), [ 21 ] while effects from CT-state coupling are known to cause signifi cantly larger changes in the V OC . [ 16c ] Transmission electron microscopy (TEM) was used to examine the bulk-heterojunction fi lms of the molecules for evidence of self-assembly and improved order.…”

Section: Consideration Of Electrostatic Interactionsmentioning

confidence: 96%

Enhanced Performance of Organic Solar Cells with Increased End Group Dipole Moment in Indacenodithieno[3,2‐b]thiophene‐Based Molecules

Intemann

Yao

Ding

et al. 2015

Adv Funct Materials

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wileyonlinelibrary.comPresently, the performance of the top molecular donors depends heavily on their degree of semicrystallinity and requires solvent additives and postprocessing techniques, such as annealing, in order to control bulk heterojunction (BHJ) morphology. [ 5 ] This causes an increase in device fabrication complexity and reduces batch-to-batch cell reproducibility.Molecular donors that are insensitive to processing conditions and that are less dependent on crystallinity for effi cient charge transport are highly desirable and may be better suited for roll-to-roll device fabrication. Among polymeric donors, one strategy that has proven successful for producing both high device effi ciencies and an insensitivity to processing conditions, is the use of fused ring ladder-type donor moieties, as the coplanar ladder-type structure provides high hole mobilities in BHJs, even in amporphous fi lms. [ 6 ] To this end, attempts have been made to incorporate the ladder-type indacenodithiophene (IDT) donor moiety into the structure of novel molecular donors, with the resulting materials indeed showing a general insensitivity to processing conditions. [ 7 ] However, these materials have exhibited very low fi ll factors (FF) in devices (0.35-0.48), likely resulting from poor morphology and charge transport in BHJs. Due to the low FF, IDT-based molecules have only achieved PCEs up to 4.7%, far lower than the 7.5% achieved by IDT-based polymers. [ 8 ] Indacenodithieno[3,2-b]thiophene (IDTT) is an alternate ladder-type donor moiety that has performed exceptionally well in polymeric semiconductors. [ 6b,d , 9 ] Its longer fused ring structure produces higher hole mobilities and extinction coeffi cients for improved light harvesting, compared to IDT in polymeric materials, while still maintaining a reasonably low sensitivity to processing conditions. We believed these features could be used to make IDTT-based molecular donors for high effi ciency OPVs.Herein, we report four new IDTT-based molecules utilizing a D1-A-D2-A-D1 type structure, where D1 is an alkyl oligiothiophene-based donor, A is a benzothiadiazole (BT) acceptor, and D2 is IDTT ( Scheme 1 ). Because the out-of-plane side chains of IDTT disrupt π-stacking, we hypothesized that π-stacking would occur primarily at the ends of the molecule, and therefore, the nature of the D1-A portion (hereafter referred to as the end group) would have a substantial effect on the morphology

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“…The concept of disorder induced tail states in HOMO and LUMO energy levels of donor and acceptor materials is introduced to explain the observed behavior of V oc . The distribution of these tail states usually follows the Gaussian distribution [34,35]. We have considered the concept of disorder parameter r, which accounts for the broadening of density of states (DOS) and has effect on V oc as shown in the modified equation [36,37]:…”

Section: Resultsmentioning

confidence: 99%

Influence of donor–acceptor materials on the photovoltaic parameters of conjugated polymer/fullerene solar cells

Sharma

Singh

Arora

et al. 2015

J Mater Sci: Mater Electron

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Organic solar cells based on poly(3-hexylthiophene-2,5-diyl): [6, 6]-phenyl-C61-butyric acid methyl ester are the most researched solar cells, but still there is a need to achieve higher efficiency and better stability. The active layer blends of poly [N-9 00 -heptadeca-nyl-2,7-carbazole-alt-5,5-(4 0 ,7 0 -di-2-thienyl-2 0 ,1 0 ,3 0 -benzo-thiadiazole)]: [6, 6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC 71 BM) show a promise in this regard. In this work, PCDTBT:PC 71 BM thin films were prepared with different blend ratios and concentrations, and were characterized for optical and morphological properties. UVvisible spectral studies showed that the absorption decreases as the acceptor concentration in the blend increases. Atomic Force Microscopy studies showed that surface roughness increases with the increase in acceptor concentration. Optimization of the active layer was carried out by using different blend ratios and concentration to achieve better performance, and it was observed that the highest efficiency was obtained at the optimized blend ratio of 1:4 and a concentration of 12 mg/ml. Further, the variation observed in the open circuit voltage with blend ratio has been explained by the disorder induced tail states in the energy levels of donor and acceptor materials.

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The density of states in thin film copper phthalocyanine measured by Kelvin probe force microscopy

Cited by 40 publications

References 13 publications

Influence of the density of states on the open-circuit voltage in small-molecule solar cells

Influence of the density of states on the open-circuit voltage in small-molecule solar cells

Enhanced Performance of Organic Solar Cells with Increased End Group Dipole Moment in Indacenodithieno[3,2‐b]thiophene‐Based Molecules

Influence of donor–acceptor materials on the photovoltaic parameters of conjugated polymer/fullerene solar cells

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