Decoding Charge Recombination through Charge Generation in Organic Solar Cells

Shoaee, Safa; Armin, Ardalan; Stolterfoht, Martin; Hosseini, Seyed Mehrdad; Kurpiers, Jona; Neher, Dieter

doi:10.1002/solr.201900184

Cited by 49 publications

(66 citation statements)

References 32 publications

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“…For the purpose of this study, P3HT:PCBM is an ideal test system. First of all, with an electron mobility of about

10^{- 3} {cm}^{2} {normalV}^{- 1} {normals}^{- 1}

and a hole mobility of about

10^{- 4} {cm}^{2} {normalV}^{- 1} {normals}^{- 1}

, the mobility contrast is well documented . Second, because of the semicrystalline nature of P3HT:PCBM with a relatively low energetic disorder, charge extraction and recombination are well described by quasiequilibrium concepts, so that drift–diffusion simulations lead to meaningful results .…”

Section: Resultsmentioning

confidence: 99%

Watching Space Charge Build Up in an Organic Solar Cell

et al. 2020

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Space charge effects can significantly degrade charge collection in organic photovoltaics (OPVs), especially in thick‐film devices. The two main causes of space charge are doping and imbalanced transport. Although these are completely different phenomena, they lead to the same voltage dependence of the photocurrent, making them difficult to distinguish. Herein, a method is introduced on how the build‐up of space charge due to imbalanced transport can be monitored in a real operating organic solar cell. The method is based on the reconstruction of quantum efficiency spectra and requires only optical input parameters that are straightforward to measure. This makes it suitable for the screening of new OPV materials. Furthermore, numerical and analytical means are derived to predict the impact of imbalanced transport on charge collection. It is shown that when charge recombination is sufficiently reduced, balanced transport is not a necessary condition for efficient thick‐film OPVs.

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“…For the purpose of this study, P3HT:PCBM is an ideal test system. First of all, with an electron mobility of about

10^{- 3} {cm}^{2} {normalV}^{- 1} {normals}^{- 1}

and a hole mobility of about

10^{- 4} {cm}^{2} {normalV}^{- 1} {normals}^{- 1}

Section: Resultsmentioning

confidence: 99%

Watching Space Charge Build Up in an Organic Solar Cell

et al. 2020

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“…There is growing consensus that the encounter of charge carriers at the donoracceptor interface goes along with the reformation of interfacial charge transfer (CT) states and that the main process behind suppressed recombination is the re-dissociation of such CT states. [14,15] In this picture, k 2 is written in terms of three factors:…”

Section: Introductionmentioning

confidence: 99%

“…There is growing consensus that the encounter of charge carriers at the donor–acceptor interface goes along with the reformation of interfacial charge transfer (CT) states and that the main process behind suppressed recombination is the re‐dissociation of such CT states. [ 14,15 ] In this picture,

k_{2}

is written in terms of three factors:

k_{2} = γ_{CT} γ_{en} k_{normalL} = γ k_{normalL}

. Here,

γ_{en} = k_{en} / k_{normalL}

describes the reduction of encounter rate compared with the Langevin model due to phase separation, and

γ_{CT} = 1 - P

is the CT recombination reduction factor, with P being the probability of (re‐)dissociation of the formed CT states.…”

Section: Introductionmentioning

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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“…[184] Several processes, such as trap-assisted recombination, bimolecular recombination, and parameters such as charge carrier mobility and lifetime play a role in maximizing the FF. [185][186][187][188][189][190][191] Trap-assisted recombination, is an inherent recombination in OPV blends, arising from the energetic disorder of organic materials. [192][193][194] Bimolecular recombination rates of holes and electrons, on the other hand, are usually referred to as Langevin recombination.…”

Section: Charge Carrier Mobility and Recombinationmentioning

confidence: 99%

The Bulk Heterojunction in Organic Photovoltaic, Photodetector, and Photocatalytic Applications

et al. 2020

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Organic semiconductors require an energetic offset in order to photogenerate free charge carriers efficiently, owing to their inability to effectively screen charges. This is vitally important in order to achieve high power conversion efficiencies in organic solar cells. Early heterojunction‐based solar cells were limited to relatively modest efficiencies (<4%) owing to limitations such as poor exciton dissociation, limited photon harvesting, and high recombination losses. The development of the bulk heterojunction (BHJ) has significantly overcome these issues, resulting in dramatic improvements in organic photovoltaic performance, now exceeding 18% power conversion efficiencies. Here, the design and engineering strategies used to develop the optimal bulk heterojunction for solar‐cell, photodetector, and photocatalytic applications are discussed. Additionally, the thermodynamic driving forces in the creation and stability of the bulk heterojunction are presented, along with underlying photophysics in these blends. Finally, new opportunities to apply the knowledge accrued from BHJ solar cells to generate free charges for use in promising new applications are discussed.

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Decoding Charge Recombination through Charge Generation in Organic Solar Cells

Cited by 49 publications

References 32 publications

Watching Space Charge Build Up in an Organic Solar Cell

Watching Space Charge Build Up in an Organic Solar Cell

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

The Bulk Heterojunction in Organic Photovoltaic, Photodetector, and Photocatalytic Applications

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