Energy level alignment of polythiophene/ZnO hybrid solar cells

Feng, Wenchun; Rangan, Sylvie; Cao, Yi; Galoppini, Elena; Bartynski, Robert; Garfunkel, Eric

doi:10.1039/c4ta00937a

Cited by 34 publications

(19 citation statements)

References 52 publications

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“…It should be noted that the incorporation of ZnO into the polymer could lead to an increase in V OC due to an energy‐level alignment between the highest occupied molecular orbital (HOMO) of P3HT and ZnO. The energy offset in the energy levels between the polymer and ZnO should push the HOMO level of P3HT down and result in a difference of 0.4–0.5 eV between the HOMO of P3HT and ZnO, as previously observed by Feng et al . In our case, the V OC remains relatively similar, probably due to various competing factors.…”

Section: Resultssupporting

confidence: 85%

Effect of additional electron acceptor in hybrid P3HT:PCBM:ZnO spin‐coated films for photovoltaic application

Muller

Ramashia

Motaung

et al. 2016

Physica Status Solidi (a)

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Concerted efforts need to be undertaken to overcome limited efficiencies and instability issues in order to ensure a niche for organic photovoltaics (OPVs) in the PV market. Recent improvements on tandem structures aside, in order to achieve further improvements it is sensible to construct test-case scenarios on bulk heterojunction cells. One aspect, involving the low mobility of charge carriers, caused by the short exciton diffusion length in the active layer, has been targeted. In this regard, attempts to incorporate inorganic semiconductors into organic blends in hybrid organic solar cells, in various configurations, have so far been promising. In this work, ZnO nanoparticles were mixed into the poly (3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend, and used as additional acceptors of electrons in the active layer. Metal-oxide interface layers between the active layer and ITO and the top contact layer, respectively, were introduced in the solar cell to compensate for environmental degradation. Thermo-gravimetric analyses of the active layers revealed improved thermal stability of P3HT upon incorporating ZnO in the polymer matrix. The photovoltaic properties demonstrated that the addition of ZnO nanoparticles in the P3HT:PCBM bulk-heterojunction solar cell causes an increase in the power conversion efficiency, while excessive loading of ZnO decreases the efficiency.

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Section: Resultssupporting

confidence: 85%

Effect of additional electron acceptor in hybrid P3HT:PCBM:ZnO spin‐coated films for photovoltaic application

Muller

Ramashia

Motaung

et al. 2016

Physica Status Solidi (a)

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“…The intense absorption band of PTB7-Th appears between 550 and 800 nm (see Figure 2b), and its reported HOMO energy level is about −5.4 eV. In addition, the spectra of a cyclic voltammogram (CV) and an ultraviolet photoelectron spectroscopy (UPS) of the two polymers, [54,55] as shown in Figure 2c,d, verify their similar HOMO level values. [53] The absorption spectrum of the PBDT-DPPD covers the region from 300 to 600 nm (see Figure 2b) and its HOMO level is about −5.4 eV.…”

Section: Resultsmentioning

confidence: 65%

“…Because the two polymers' absorption bands are in different parts of the solar spectrum, a considerable enhancement in solar spectrum absorption is expected when the polymers are blended. In addition, the spectra of a cyclic voltammogram (CV) and an ultraviolet photoelectron spectroscopy (UPS) of the two polymers, [54,55] as shown in Figure 2c,d, verify their similar HOMO level values. The HOMO energy levels for PBDT-DPPD and PTB7-Th as obtained from CV measurement were −5.45 and −5.40 eV, and as obtained from UPS measurement were −5.46 and −5.40 eV, respectively.…”

Section: Resultsmentioning

confidence: 75%

Overcoming Fill Factor Reduction in Ternary Polymer Solar Cells by Matching the Highest Occupied Molecular Orbital Energy Levels of Donor Polymers

Lee

Tamilavan

Rho

et al. 2017

Advanced Energy Materials

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Despite the potential of ternary polymer solar cells (PSCs) to improve photocurrents, ternary architecture is not widely utilized for PSCs because its application has been shown to reduce fill factor (FF). In this paper, a novel technique is reported for achieving highly efficient ternary PSCs without this characteristic sharp decrease in FF by matching the highest occupied molecular orbital (HOMO) energy levels of two donor polymers. Our ternary device—made from a blend of wide‐bandgap poly[4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione) (PBDT‐DPPD) polymer, narrow‐bandgap poly[4,8‐bis[5‐(2‐ethylhexyl)‐2‐thienyl]benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐ 6‐diyl)] (PTB7‐Th) polymer, and [6,6]‐phenyl C70‐butyric acid methyl ester (PC70BM)—exhibits a maximum power conversion efficiency of 10.42% with an open‐circuit voltage of 0.80 V, a short‐circuit current of 17.61 mA cm−2, and an FF of 0.74. In addition, this concept is extended to quaternary PSCs made by using three different donor polymers with similar HOMO levels. Interestingly, the quaternary PSCs also yield a good FF (≈0.70)—similar to those of corresponding binary PSCs. This study confirms that the HOMO levels of the polymers used on the photoactive layer of PSCs are a crucial determinant of a high FF.

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“…The 4 orders of magnitude improvement in conductivity indicates GO was reduced to RGO. 45,46 The work function of RGO is 4.5 eV probed by UPS, which is larger than the reported work function of graphene prepared by chemical vapor deposition method. 47 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 barrier for electrons from Au to ZnO of 1.2 eV (Figure 4e).…”

Section: Surface Characterizationsmentioning

confidence: 86%

Sponge-Templated Macroporous Graphene Network for Piezoelectric ZnO Nanogenerator

Chen

Kumar

et al. 2015

ACS Appl. Mater. Interfaces

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We report a simple approach to fabricate zinc oxide (ZnO) nanowire based electricity generators on three-dimensional (3D) graphene networks by utilizing a commercial polyurethane (PU) sponge as a structural template. Here, a 3D network of graphene oxide is deposited from solution on the template and then is chemically reduced. Following steps of ZnO nanowire growth, polydimethylsiloxane (PDMS) backfilling and electrode lamination completes the fabrication processes. When compared to conventional generators with 2D planar geometry, the sponge template provides a 3D structure that has a potential to increase power density per unit area. The modified one-pot ZnO synthesis method allows the whole process to be inexpensive and environmentally benign. The nanogenerator yields an open circuit voltage of ∼0.5 V and short circuit current density of ∼2 μA/cm(2), while the output was found to be consistent after ∼3000 cycles. Finite element analysis of stress distribution showed that external stress is concentrated to deform ZnO nanowires by orders of magnitude compared to surrounding PU and PDMS, in agreement with our experiment. It is shown that the backfilled PDMS plays a crucial role for the stress concentration, which leads to an efficient electricity generation.

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Energy level alignment of polythiophene/ZnO hybrid solar cells

Abstract: A change in the interface dipole lowers the polythiophene energy levels, increasing both theoretical and actual Voc of polythiophene/ZnO photovoltaics.

Cited by 34 publications

References 52 publications

Effect of additional electron acceptor in hybrid P3HT:PCBM:ZnO spin‐coated films for photovoltaic application

Effect of additional electron acceptor in hybrid P3HT:PCBM:ZnO spin‐coated films for photovoltaic application

Overcoming Fill Factor Reduction in Ternary Polymer Solar Cells by Matching the Highest Occupied Molecular Orbital Energy Levels of Donor Polymers

Sponge-Templated Macroporous Graphene Network for Piezoelectric ZnO Nanogenerator

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