Watching Space Charge Build Up in an Organic Solar Cell

Wilken, Sebastian; Sandberg, Oskar J.; Scheunemann, Dorothea; Österbacka, Ronald

doi:10.1002/solr.201900505

Cited by 32 publications

(31 citation statements)

References 49 publications

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“…As previously discussed in the literature, the drop in the FF can be understood in terms of increased bimolecular recombination losses [24,25] during charge transport or space charge effects either due to doping or imbalanced carrier mobilities. [26][27][28][29] The efficiency limitation that comes with lower FF in thick junction devices can be illustrated with numerical drift-diffusion (D-D) simulations. To this end, we performed automat for simulation of heterostructures (AFORS-HET) simulations; [30] the simulation numerically solves the D-D equations that govern the J-V characteristics of the device, thus explicitly considering the effect of free carrier recombination coefficient, surface recombination, carrier mobilities of the active layer, and layer thicknesses.…”

Section: Resultsmentioning

confidence: 99%

Putting Order into PM6:Y6 Solar Cells to Reduce the Langevin Recombination in 400 nm Thick Junction

et al. 2020

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Increasing the active layer thickness without sacrificing the power conversion efficiency (PCE) is one of the great challenges faced by organic solar cells (OSCs) for commercialization. Recently, PM6:Y6 as an OSC based on a non‐fullerene acceptor (NFA) has excited the community because of its PCE reaching as high as 15.9%; however, by increasing the thickness, the PCE drops due to the reduction of the fill factor (FF). This drop is attributed to change in mobility ratio with increasing thickness. Furthermore, this work demonstrates that by regulating the packing and the crystallinity of the donor and the acceptor, through volumetric content of chloronaphthalene (CN) as a solvent additive, one can improve the FF of a thick PM6:Y6 device (≈400 nm) from 58% to 68% (PCE enhances from 12.2% to 14.4%). The data indicate that the origin of this enhancement is the reduction of the structural and energetic disorders in the thick device with 1.5% CN compared with 0.5% CN. This correlates with improved electron and hole mobilities and a 50% suppressed bimolecular recombination, such that the non‐Langevin reduction factor is 180 times. This work reveals the role of disorder on the charge extraction and bimolecular recombination of NFA‐based OSCs.

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Section: Resultsmentioning

confidence: 99%

Putting Order into PM6:Y6 Solar Cells to Reduce the Langevin Recombination in 400 nm Thick Junction

et al. 2020

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“…Whereas the light‐intensity dependence of space charge caused by asymmetric mobilities has already been analyzed by Wilken et al., [ 59 ] the influence on the J sc –Φ relation of the space‐charge region due to defect states as observed in Figure 6 still has to be investigated. For this purpose, Figure shows the slope γ = d(ln( J sc ))/d(ln(Φ)) as a function of illumination Φ For a realistic device in Figure 7a, there is substantial nonlinearity occurring at lower light intensities than in Figure 7b for a device with high relative permittivity and therefore constant electric field.…”

Section: Resultsmentioning

confidence: 99%

“…who additionally considered the spatial dependence of the electron and hole current. [ 59 ] The correlation has already been used in previous studies to identify space‐charge limited photocurrent in organic solar cells with asymmetric carrier mobilities. [ 30,45 ] However, Equation (12) is only valid in a defect free device with sharp band edges.…”

Section: Theorymentioning

confidence: 99%

Understanding the Light‐Intensity Dependence of the Short‐Circuit Current of Organic Solar Cells

Hartnagel

Kirchartz

2020

Advcd Theory and Sims

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In organic solar cells, bimolecular recombination is a key factor limiting the device performance and creating the need for characterization. Light‐intensity‐dependent short‐circuit current density measurements are a frequently used tool to qualitatively analyze bimolecular recombination in a device. When applying a 0D model, bimolecular recombination is expected to reduce the otherwise linear correlation of the short‐circuit current density Jsc and the light intensity Φ to a sublinear trend. It is shown by numerical simulations that the slope of the Jsc–Φ curve is affected by the recombination mechanism (direct or via traps), the spatial distribution of charge carriers and—in thick solar cells—by space charge effects. Only the combination of these effects allows proper explanation of the different cases, some of which cannot be explained in a simple 0D device model.

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“…[ 43,57 ] Also, a light‐intensity dependent space‐charge region has been observed for asymmetric mobilities. [ 39,58–60 ] However, in the case of asymmetric mobilities the space charge builds up at the contact where the less mobile charge carriers are extracted. [ 39,58,59 ] In contrast, Wu et al.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

The Influence of Photo‐Induced Space Charge and Energetic Disorder on the Indoor and Outdoor Performance of Organic Solar Cells

Beuel

Hartnagel

Kirchartz

2021

Advcd Theory and Sims

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Apart from traditional large‐scale outdoor application, organic solar cells are also of interest for powering small, off‐grid electronic devices indoors. For operation under the low light intensities that are typical for indoor application, a high shunt resistance is required calling for thick active layers in industrial processing to ensure maximum coverage. However, the thickness of an organic solar cell based on energetically disordered semiconductors is limited by space‐charge effects from charged shallow defects under nonuniform generation. While other sources of space charge such as doping and asymmetric transport have been extensively discussed in previous studies, this work offers a theoretical analysis of this photo‐induced space charge in shallow defects and visualizes how the space charge builds up with increasing light intensity with drift‐diffusion simulations. It is shown that the effect particularly deteriorates the performance of an organic solar cell with high active‐layer thickness and substantial energetic disorder. However, the simulations reveal that solar cells are less sensitive to these parameters under low light intensities due to a reduced density of photo‐induced space charge. Therefore, a wider range of material systems and absorber thicknesses can be viable for indoor applications than one may initially expect from testing under 1 sun illumination.

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Watching Space Charge Build Up in an Organic Solar Cell

Cited by 32 publications

References 49 publications

Putting Order into PM6:Y6 Solar Cells to Reduce the Langevin Recombination in 400 nm Thick Junction

Putting Order into PM6:Y6 Solar Cells to Reduce the Langevin Recombination in 400 nm Thick Junction

Understanding the Light‐Intensity Dependence of the Short‐Circuit Current of Organic Solar Cells

The Influence of Photo‐Induced Space Charge and Energetic Disorder on the Indoor and Outdoor Performance of Organic Solar Cells

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