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Recovering lost excitons in organic photovoltaics using a transparent dissociation layer
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Image of FIG. 1.
FIG. 1.

(a) Active molecules used within this study and their absorption spectra calculated from refractive index values measured by spectroscopic ellipsometry. (b) An energy level diagram for a SubPc/C device with an α-NPD exciton dissociation layer inserted between the SubPc and MoO layers.

Image of FIG. 2.
FIG. 2.

Modeled (a) electric field, (b) exciton generation, and (c) exciton population density profiles within the OPV device used in this study. Boundary conditions (which only affect the exciton population density) at the SubPc/MoO or SubPc/α-NPD interface are shown for both perfect exciton reflection ( = 0) and 100% exciton quenching or dissociation ( = 0).

Image of FIG. 3.
FIG. 3.

(a) Device structures for α-NPD/SubPc/C, SubPc/C, and α-NPD/SubPc OPV cells. (b) data under 1-sun illumination for α-NPD/SubPc (squares), SubPc/C (triangles), and α-NPD/SubPc/C (circles) devices. (c) For each device, experimental EQE data (solid lines) are compared to model (dashed lines).

Image of FIG. 4.
FIG. 4.

Experimentally determined absorption and emission spectra for SubPc/Spacer/MoO stacks deposited on glass. Inset: normalized quantum yield measurements for each stack. Quantum yield was determined using no spacer as well as spacers of BCP and α-NPD.

Image of FIG. 5.
FIG. 5.

Experimentally determined (a) , (b) EQE, and (c) IQE data for glass/ITO/MoO (5 nm)/α-NPD ( nm)/SubPc (13 nm)/C (36 nm)/BCP (10 nm)/Al (100 nm). Three α-NPD thicknesses are shown: 0 nm (triangles), 2 nm (squares), and 5 nm (circles). Modeled EQE and IQE (dotted lines) are shown with three possible boundary conditions at the SubPc/MoO or SubPc/α-NPD interface: 100% quenching, exciton reflection (Single HJ), and 100% dissociation (Cascade).

Image of FIG. 6.
FIG. 6.

Dependence of (a) , EQE at λ = 585 nm, (b) , FF, and (c) PCE on α-NPD layer thickness for a device comprising glass/ITO/MoO (5 nm)/α-NPD ( nm)/SubPc (13 nm)/C (36 nm)/BCP (10 nm)/Al (100 nm). Error bars represent standard deviations calculated from a sample size of > 8 devices.

Image of FIG. 7.
FIG. 7.

AFM images of (a) ITO/MoO (5 nm), (b) ITO/MoO (5 nm)/α-NPD (5 nm), (c) ITO/MoO (5 nm)/SubPc (13 nm), and (d) ITO/MoO (5 nm)/α-NPD (5 nm)/SubPc (13 nm). (e) Grain size and values for each sample and (f) XRD scans of MoO (5 nm)/SubPc (13 nm) and MoO (5 nm)/α-NPD (5 nm)/SubPc (13 nm), as well as a crystalline control sample of 13 nm SubPc annealed for 15 min at 95 °C.


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Table I.

Literature and fitted values of exciton lifetimes and diffusion lengths for active materials used in this study.

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Table II.

Champion solar cell performance data for the structure: Glass/ITO/MoO (5 nm)/α-NPD ( nm)/SubPc (13 nm)/C (36 nm)/BCP (10 nm)/Al (100 nm) under simulated 1-sun, AM1.5 G illumination.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Recovering lost excitons in organic photovoltaics using a transparent dissociation layer