N-Doping improves charge transport and morphology in the organic non-fullerene acceptor O-IDTBR

Paterson, Alexandra F.; Li, Ruipeng; Markina, A.; Tsetseris, Leonidas; Macphee, Sky; Faber, Hendrik; Emwas, Abdul‐Hamid; Panidi, Julianna; Bristow, Helen; Wadsworth, Andrew; Baran, Derya; Andrienko, Denis; Heeney, Martin; McCulloch, Iain; Anthopoulos, Thomas D.

doi:10.1039/d0tc05861k

Cited by 24 publications

(22 citation statements)

References 60 publications

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“…Furthemore, electron affinities lower than −3 eV ensure trap-free electron transport. [63] In fact, NFAs often exhibit ambipolar transport [63,64] as their ionization energies are normally above 6 eV. Rigid planar cores and large electronic couplings result in superior exciton diffusion lengths, up to 50 nm.…”

Section: Discussionmentioning

confidence: 99%

Chemical Design Rules for Non‐Fullerene Acceptors in Organic Solar Cells

Markina

Lin

Liu

et al. 2021

Advanced Energy Materials

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while fullerene-based OSCs are only 10% efficient. [13] To achieve this milestone, various design strategies have been explored, for example, modification/manipulation of the Y6 acceptor side chain design, [7] the use of ternary mixtures with a vertical phase distribution, [9] the chemical modification via chlorination [8] or a variation of a fused-ring acceptor block of the donor polymer. [10] Currently, NFAs match their inorganic counterparts in terms of current generation, but are lacking with regard to their open-circuit voltage. [14] Efficiency losses can be traced back to energy losses during the photon to free charge conversion, and are in generally lower than in the fullerene-based cells. [15][16][17] Free charge generation in organic solar cells is comprised of two steps. During the first step, a photogenerated exciton dissociates at the donor-acceptor interface into an interfacial charge transfer (CT) state. During this process, the ionization energy or electron affinity offset at the heterojunction provides the driving force for the hole or electron transfer. It is known that this offset should exceed a threshold value in order to enable efficient dissociation of the excited state. [18][19][20] For NFAs, only ionization energy offsets are relevant, because of the fast energy transfer from donors to acceptors. [20] During the second step of charge separation, the interfacial CT state dissociates into a pair of free charges, or the charge separated (CS) state. This dissociation is expected to be an endothermic process, and the exact mechanism behind the driving force for this process is still under debate. [21][22][23][24][25][26] It is, however, one of the key processes in OSCs, since the energetics and dynamics of the dissociating CT state determines the open circuit voltage of organic heterojunctions. [25,[27][28][29] Both steps involved in the free charge generation can be optimized by an appropriate design of the donor-acceptor pair. The main difficulty in formulating generic chemical design rules for OSC materials is that any changes to the chemical structure simultaneously modify the open-circuit voltage, V oc , the short-circuit current, J sc , and the fill factor of the solar cell. [30][31][32][33][34][35] Without knowing how these changes correlate with each other, it is impossible to formulate clear design rules and hence speed up the discovery of efficient donor-acceptor combinations.In this work, we identify the microscopic origin of such correlations and propose clear chemical design rules for NFAs. Efficiencies of organic solar cells have practicallydoubled since the development of non-fullerene acceptors (NFAs). However, generic chemical design rules for donor-NFA combinations are still needed. Such rules are proposed by analyzing inhomogeneous electrostatic fields at the donor-acceptor interface. It is shown that an acceptor-donor-acceptor molecular architecture, and molecular alignment parallel to the interface, results in energy level bending that destabilizes the charge transfer state...

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Section: Discussionmentioning

confidence: 99%

Chemical Design Rules for Non‐Fullerene Acceptors in Organic Solar Cells

Markina

Lin

Liu

et al. 2021

Advanced Energy Materials

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“…O-IDTBR devices exhibit the highest µ e of 0.35 cm 2 V -1 s -1 in agreement with previous reports. [51] Next, DQ was introduced by mixing it directly with the NFA in the same solution. The DQ concentration varied from 0 to 1 wt.% of the total solid mass of the NFA and the impact on the device operation was studied.…”

Section: Resultsmentioning

confidence: 99%

Addition of Diquat Enhances the Electron Mobility in Various Non‐Fullerene Acceptor Molecules

Nugraha

Gedda

Firdaus

et al. 2022

Adv Funct Materials

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Molecular doping of organic semiconductors is often used to enhance their charge transport characteristics. Despite its success, however, most studies to date concern p-doping with considerably fewer reports involving n-dopants. Here, n-doping of organic thin-film transistors (OTFTs) based on several non-fullerene acceptor (NFA) molecules using the recently developed diquat (DQ) as a soluble molecular dopant is reported. The low ionization potential of DQ facilitates efficient electron transfer and subsequent n-doping of the NFAs, resulting in a consistent increase in the electron field-effect mobility. Solution-processed BTP-eC9 and N3-based OTFTs exhibit significant increase in the electron mobility upon DQ doping, with values increasing from 0.02 to 0.17 cm 2 V -1 s -1 and from 0.2 to 0.57 cm 2 V -1 s -1 , respectively. A remarkable electron mobility of >1 cm 2 V -1 s -1 is achieved for O-IDTBR transistors upon optimal doping with DQ. The enhanced performance originates primarily from synergistic effects on electronic transport and changes in morphology, including: i) significant reduction of contact resistances, ii) formation of larger crystalline domains, iii) change of preferred crystal orientation, and iv) alteration in molecular packing motif. This work demonstrates the universality of DQ as an electronic additive for improving electron transport in OTFTs.

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“…Furthemore, electron affinities lower than -3 eV ensure trap-free electron transport [63]. In fact, NFAs often exhibit ambipolar transport [63,64] as their ionization energies are normally above 6 eV. Rigid planar cores and large electronic couplings result in superior exciton diffusion lengths, up to 50 nm [65].…”

Section: Discussionmentioning

confidence: 99%

Chemical design rules for non-fullerene acceptors in organic solar cells

Markina,

Lin,

Liu

et al. 2022

Preprint

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Efficiencies of organic solar cells have practically doubled since the development of non-fullerene acceptors (NFAs). However, generic chemical design rules for donor-NFA combinations are still needed. We propose such rules by analyzing inhomogeneous electrostatic fields at the donor-acceptor interface. We show that an acceptor-donor-acceptor molecular architecture, and molecular alignment parallel to the interface, result in energy level bending that destabilizes the charge transfer state, thus promoting its dissociation into free charges. By analyzing a series of PCE10:NFA solar cells, with NFAs including Y6, IEICO, and ITIC, as well as their halogenated derivatives, we suggest that the molecular quadrupole moment of ca 75 Debye Å balances the losses in the open circuit voltage and gains in charge generation efficiency.

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N-Doping improves charge transport and morphology in the organic non-fullerene acceptor O-IDTBR

Abstract: Doping improves critical performances metrics in electronic devices. Research into n-doped organic small molecules is comparatively limited, because of a historical combined lack of available n-dopants and unfavourable microstructural effects....

Cited by 24 publications

References 60 publications

Chemical Design Rules for Non‐Fullerene Acceptors in Organic Solar Cells

Chemical Design Rules for Non‐Fullerene Acceptors in Organic Solar Cells

Addition of Diquat Enhances the Electron Mobility in Various Non‐Fullerene Acceptor Molecules

Chemical design rules for non-fullerene acceptors in organic solar cells

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