Fast charge separation in a non-fullerene organic solar cell with a small driving force

Liu, Jing; Chen, Shangshang; Qian, Deping; Gautam, Bhoj; Yang, Guofang; Zhao, Jingbo; Bergqvist, Jonas; Zhang, Fengling; Ma, Wei; Ade, Harald; Inganäs, Olle; Gündoğdu, Kenan; Gao, Feng; Yan, He

doi:10.1038/nenergy.2016.89

Cited by 1,224 publications

(1,175 citation statements)

References 42 publications

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“…[34,40] However, only few of these cells still have high IPCE and PCE. [41] Another means of increasing the V OC of OPVs is the implementation of interlayers. Instead of a single D-A heterojunction one or more additional layers are inserted between donor and acceptor so that the lowest unoccupied and the highest occupied molecular orbitals (LUMO/HOMO) of all materials form an energy cascade.…”

Section: Reducing the Driving Forcementioning

confidence: 99%

Energy Losses in Small‐Molecule Organic Photovoltaics

Linderl

Zechel

Brendel

et al. 2017

Advanced Energy Materials

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processible PV technology has recently appeared as well. [5] Comparing the different technologies in terms of PCE, which is specified as the product of the short-circuit current density j SC , the open-circuit voltage V OC and the fill factor FF divided by the incoming light intensity under standard AM 1.5G illumination conditions, OPVs can well compete with their inorganic counterparts in terms of j SC or, more precisely, the external quantum efficiency and also with minor trade-off in FF, but clearly suffer from lower V OC at a given energy gap E g of the light absorbing material. While this socalled bandgap-voltage offset can be as low as 0.3-0.4 eV in Si and GaAs [6] and only a little larger in perovskite cells, [7] OPV cells exhibit energy losses of at least 0.6 eV -in many cases, however, this offset can approach and even exceed 1 eV. [8] This is currently one of the main bottlenecks toward making OPVs competitive with inorganic PV cells.In this research news, we provide the required background information on the appearance of energy losses in OPV cells, by which we mean the difference between the equivalent of the optical gap and the measured open-circuit voltage that is frequently also denoted as voltage loss, and discuss recent progress toward better understanding their origin and strategies to reduce them. To keep focused, we will mainly address small molecules as active organic semiconductors, which are being processed into thin films by vacuum deposition techniques. Compared to frequently studied π-conjugated polymers, the synthesis of small molecules is more reproducible. Moreover, a rigorous purification of small molecules is easier, which gives the opportunity to reproducibly investigate well-defined systems. The application of vacuum deposition techniques prevents the use of solvents, which as a third component in wet chemical processing can strongly influence the morphology. [9] Thus, active layers of small molecules prepared by vacuum deposition methods mark a well-controlled model system for fundamental studies such as the origin of energy losses in OPV devices. However, we expect that most of the findings can be transferred to solution-processed OPVs as well, which have considerably higher complexity in terms of local morphology and phase behavior. Excitonic Organic Solar CellsIn order to properly address energy losses in OPVs it is useful to look at their working principles in more detail (see also [10] ).

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Section: Reducing the Driving Forcementioning

confidence: 99%

Energy Losses in Small‐Molecule Organic Photovoltaics

Linderl

Zechel

Brendel

et al. 2017

Advanced Energy Materials

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show abstract

“…To date, most of the successful NFAs are derived from strong electron deficient units, such as aromatic diimides (perylene diimides, naphthalene diimides, etc.) [9][10][11][12][13][14][15][16][17], dicyanovinyl [18][19][20], diketopyrrolopyrrole [21,22], and benzothiadiazole [23,24]. Among them, rod-like acceptordonor-acceptor (A-D-A) structured molecules in which an electron-rich fused-ring core is used as a central donor and two strong electron-withdrawing groups are used as acceptors, are promising for high performance OSCs because their optical and electronic properties can be easily tuned by varying the fused-ring core or the terminal groups, in comparison with those of fullerene-based electron acceptors or aromatic diimide-based NFAs [25][26][27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Asymmetric indenothiophene-based non-fullerene acceptors for efficient polymer solar cells

et al. 2017

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“…Current research efforts are thus intensely focused on tailoring the properties of the CT state at the donor/acceptor interface for further improvements in open-circuit voltage 48 . In fact, recently reported high efficiency OPV materials do show CT energies that are almost identical to the optical gap 41 , significantly improving the open-circuit voltage. The next generation of high efficiency OPV materials is thus expected to have efficient exciton dissociation with a negligible driving force and a CT energy equal to the optical gap, leading to improved VOC.…”

Section: Open-circuit Voltagementioning

confidence: 97%

“…Concomitantly, the VOC of an organic solar cell is generally lower by at least 0.1-0.3 eV compared to an inorganic solar cell with the same optical gap. New materials, enabling efficient charge separation with negligible driving force 40,41 , have been developed and show improved VOC 41 . The future of BHJ organic solar cells relies on such materials.…”

Section: Exciton Dissociationmentioning

confidence: 99%

Non-Equilibrium Charge Motion in Organic Solar Cells

Melianas¹

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Fast charge separation in a non-fullerene organic solar cell with a small driving force

Cited by 1,224 publications

References 42 publications

Energy Losses in Small‐Molecule Organic Photovoltaics

Energy Losses in Small‐Molecule Organic Photovoltaics

Asymmetric indenothiophene-based non-fullerene acceptors for efficient polymer solar cells

Non-Equilibrium Charge Motion in Organic Solar Cells

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