Using the Stark effect to understand charge generation in organic solar cells

Jonghe-Risse, Jelissa De; Causa, Martina; Buchaca‐Domingo, Ester; Heeney, Martin; Moser, Jacques-E.; Stingelin, Natalie; Banerji, Natalie

doi:10.1117/12.2190212

Cited by 3 publications

(3 citation statements)

References 15 publications

(21 reference statements)

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“…Importantly, these molecules must lie at or near the interface between n-and p-type semiconductors. The observed EA signal resembles the first derivative of the absorption spectra of these molecules (see more details in the SI, Section S4), as reported in the literature on TA measurements 11,29,30 and steady-state EA experiments 31 . Integrating this over photon energy gives the ground state absorption spectra of these molecules.…”

supporting

confidence: 77%

“…As illustrated in Figure 1 This EA signal has been used to create powerful pump-probe methods to investigate the interfaces of inorganic and organic material systems. 11,[28][29][30] Recently, we have demonstrated that this EA can be tracked as a function of time at BHJ interfaces. As the e-h pair separates across the interface, the electric field associated with it varies, giving rise to a time-dependent electric field and hence a time-dependent Stark shift and EA signal.…”

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confidence: 99%

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Visualizing excitations at buried heterojunctions in organic semiconductor blends

et al. 2017

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Interfaces play a crucial role in semiconductor devices, but in many device architectures they are nanostructured, disordered and buried away from the surface of the sample. Conventional optical, X-ray and photoelectron probes often fail to provide interface-specific information in such systems. Here we develop an all-optical time-resolved method to probe the local energetic landscape and electronic dynamics at such interfaces, based on the Stark effect caused by electron-hole pairs photo-generated across the interface. Using this method, we found that the electronically active sites at the polymer/fullerene interfaces in model bulk-heterojunction blends fall within the low-energy tail of the absorption spectrum. This suggests that these sites are highly ordered compared with the bulk of the polymer film, leading to large wavefunction delocalization and low site energies. We also detected a 100 fs migration of holes from higher- to lower-energy sites, consistent with these charges moving ballistically into more ordered polymer regions. This ultrafast charge motion may be key to separating electron-hole pairs into free charges against the Coulomb interaction.

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confidence: 77%

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confidence: 99%

Visualizing excitations at buried heterojunctions in organic semiconductor blends

et al. 2017

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“…The set-ups for femtosecond TA and EDA spectroscopy were closely related and based on a pump–probe scheme that we have previously described 25 59 . In brief, we used an amplified Ti:sapphire laser system (CPA-2001, Clark-MXR) with a 1 kHz repetition rate and output wavelength of 780 nm.…”

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confidence: 99%

The fate of electron–hole pairs in polymer:fullerene blends for organic photovoltaics

et al. 2016

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There has been long-standing debate on how free charges are generated in donor:acceptor blends that are used in organic solar cells, and which are generally comprised of a complex phase morphology, where intermixed and neat phases of the donor and acceptor material co-exist. Here we resolve this question, basing our conclusions on Stark effect spectroscopy data obtained in the absence and presence of externally applied electric fields. Reconciling opposing views found in literature, we unambiguously demonstrate that the fate of photogenerated electron–hole pairs—whether they will dissociate to free charges or geminately recombine—is determined at ultrafast times, despite the fact that their actual spatial separation can be much slower. Our insights are important to further develop rational approaches towards material design and processing of organic solar cells, assisting to realize their purported promise as lead-free, third-generation energy technology that can reach efficiencies over 10%.

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Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems

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et al. 2017

Structural Dynamics

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Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research “Molecular Ultrafast Science and Technology,” a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.

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Using the Stark effect to understand charge generation in organic solar cells

Cited by 3 publications

References 15 publications

Visualizing excitations at buried heterojunctions in organic semiconductor blends

Visualizing excitations at buried heterojunctions in organic semiconductor blends

The fate of electron–hole pairs in polymer:fullerene blends for organic photovoltaics

Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems

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