Universal Design Principles for Cascade Heterojunction Solar Cells with High Fill Factors and Internal Quantum Efficiencies Approaching 100%

Barito, Adam; Sykes, Matthew E.; Huang, Bingyuan; Bilby, David; Frieberg, Bradley; J, Kim; Green, Peter; Shtein, Max

doi:10.1002/aenm.201400216

Cited by 37 publications

(40 citation statements)

References 46 publications

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“…With this purpose, we choose the melting points of the 11 Table 3: Experimental unit cells (e) and simulated ones (s) with the united atom R3 and R3 ǫ − 8% force fields, and full atom FA (AMBER95 plus PBE0/def2-TZVP point charges) and T-FA force fields (identical to FA but with reparameterized dihedrals). Densities ρ are expressed in g/cm 3 , cell volumes inÅ 3 , sides inÅ, and angles in degrees. The angles, where equal to 90 degrees in the experimental cell, were kept fixed to this value during the simulation.…”

Section: Tuning Of Lennard-jones Potential Well Depthsmentioning

confidence: 99%

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

Moral

Son

Sancho‐García

et al. 2015

J. Chem. Theory Comput.

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A united atom force field is empirically derived by minimizing the difference between experimental and simulated crystal cells and melting temperatures for eight compounds representative of organic electronic materials used in OLEDs and other devices: biphenyl, carbazole, fluorene,9, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ture also for two larger compounds employed as hosts in phosphorescent and thermally activated delayed fluorescence OLEDs:The good performances of the force field, coupled to the large computational saving granted by the united atom approximation, make it an ideal choice for the simulation of the morphology of emissive layers for OLED materials in crystalline or glassy phases.

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Section: Tuning Of Lennard-jones Potential Well Depthsmentioning

confidence: 99%

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

Moral

Son

Sancho‐García

et al. 2015

J. Chem. Theory Comput.

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“…Since recombination is limited by the carrier with the lowest carrier concentration, recombination rates will remain low until a sufficient number of opposite carriers populate and V OC will only follow the outermost HOMO-LUMO offset if an alternative radiative state or non-radiative mechanism exists at that energy level. In the two cascade devices containing SubPc, V OC is substantially less than V c , likely due to impaired photocurrent resulting from excessive charge accumulation at the ClAlPc/SubPc heterojunction which can cause an electric field opposing the photocurrent [16,26]. We expect that further work to optimize layer thicknesses or employ alternative material sets will maximize photocurrent and minimize parasitic charge build-up, ultimately bringing V OC of cascade devices closer to V c and exceeding the outermost HOMO-LUMO offset by a wider margin.…”

Section: Resultsmentioning

confidence: 98%

“…Previous observations of V OC in cascade structures have found that adding an additional layer to a bi-layer cell, resulting in an energy loss step, does not reduce V OC appreciably [4,14]. However, others have observed the opposite [2,15] or mixed results [16,17]. The implications for device theoretical efficiencies and design rules are significant because the lowest value of DE DA can be substantially greater than the outermost HOMO-LUMO offset, allowing for higher V OC and a greater number of cascade layers.…”

Section: Introductionmentioning

confidence: 88%

Open-circuit voltage exceeding the outermost HOMO-LUMO offset in cascade organic solar cells

Stevens

Arango

2016

Organic Electronics

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a b s t r a c tWe demonstrate a planar organic solar cell with a four-layer cascade architecture that exhibits an opencircuit voltage (Voc) greater than the offset in energy between the highest occupied molecular orbital (HOMO) of the outermost donor and the lowest unoccupied molecular orbital (LUMO) of the outermost acceptor. The device consists of a subphthalocyanine (SubPc)/fullerene (C60) heterojunction that is modified by inserting one or two additional donor layers between SubPc and the anode. We find that two-, three-and four-layer structures yield similar Voc (1.0 V, 0.91 V and 0.94 V, respectively), even though the outermost HOMO-LUMO offset decreases from 1.4 eV to 1.10 eV, and to 0.9 eV, respectively. Analysis of the turn-on voltage in dark provides further evidence that open-circuit voltage is not limited by the outermost HOMO-LUMO offset.

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“…Three or more active single layers with carefully adjusted energy levels lead to high external quantum effi ciencies (EQE) over a broad spectral region, while containing a high open circuit voltage ( V OC ) and suffi cient short circuit current densities ( j SC ). [5][6][7] Additional research focus lies on the development of alternatives to fullerene-derivative acceptors which are commonly used but provide limited absorption. [ 8,9 ] Cnops et al recently reported highly effi cient fullerene-free organic cascade devices employing the vacuum-deposited organic materials α-6T, SubPc, and SubNc as active layers.…”

Section: Doi: 101002/aenm201502432mentioning

confidence: 99%

Degradation of Sexithiophene Cascade Organic Solar Cells

Bormann

Nehm

Weiß

et al. 2016

Advanced Energy Materials

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fl exibility or light weight required for fl exible OPV. Atomic layer deposited (ALD) oxide thin-fi lms (e.g. SiO x , AlO x ) provide fl exibility and low WVTR rates at the same time. [22][23][24] This work is motivated by two factors: First, a lifetime study for cascade organic solar cells (CSCs) under ambient climate conditions has not been performed up to now, making the evaluation of their applicability diffi cult. Second, only a few publications show highly effi cient organic solar cells on silver nanowire electrodes. Beyond that, all devices exhibiting a PCE >5% on AgNW electrodes used polymer donors. [25][26][27] In this study, we show aging experiments on organic solar cells with the small molecules α-6T/SubNc/SubPc as cascade. [ 10 ] We compare rigid glass-glass encapsulated devices with ITO bottom electrodes to fully fl exible devices. AgNWs are utilized as transparent electrode, ALD thin-fi lms of alumina serve as fl exible ultra-barrier. The planarization of AgNWs is challenging, as they exhibit high surface roughness which usually causes the organic thin-fi lm device to shunt. Many different planarization techniques have been successfully employed using poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), metal oxides, or small molecules. [ 17,[28][29][30][31][32] Another method uses a peel-off process whereby the silver nanowires are buried in a polymer substrate. [ 25,[33][34][35] We employ the AgNW planarization concept recently demonstrated by Cui et al., [ 36 ] where the AgNWs are buried in the UV-curable optical adhesive "NOA63". This polymer serves as ultrathin and ultrafl exible substrate for the highly conductive AgNW network. Figure 1 shows the electrode fabrication and characterization by means of topographical and optical analysis. Silver nanowires with 35 nm diameter (NW35) are used to transfer the NOA63 into a conductive substrate (details can be found in the Experimental Section).Atomic force microscopy (AFM) measurements reveal that the root-mean-square roughness of the electrode is in the range of 1 to 2 nm (Figure 1 B). Furthermore, the strong phase contrast in Figure 1 C shows that AgNWs protrude from the NOA63 surface. This guarantees an electrical contact to adjacent conductive layers. A sheet resistance ( R S ) of (18.5 ± 0.2) Ω/sq is measured for this electrode even though the maximum processing temperature is only 80 °C. The electrode exhibits a total transmission of 84.5% at a wavelength of 550 nm which is comparable to NW35 on glass. However, plasmonic nanowire absorption, which is already present in the neat glass/NW35 electrode, broadens upon embedding in the polymer. This stronger plasmonic absorption in the spectral region between 350 and 500 nm reduces the average total transmission in the visible light spectrum T av to 82.8% as compared to 83.9% of NW35 on glass. Although ITO on glass exhibits a T av of 84.3%, its R S of 26 Ω/sq is higher than for the NW35 electrode.This ultrasmooth, highly conductive, and transparent AgNW electrode is well suitable for ...

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Universal Design Principles for Cascade Heterojunction Solar Cells with High Fill Factors and Internal Quantum Efficiencies Approaching 100%

Cited by 37 publications

References 46 publications

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

Open-circuit voltage exceeding the outermost HOMO-LUMO offset in cascade organic solar cells

Degradation of Sexithiophene Cascade Organic Solar Cells

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