Changing molecular band offsets in polymer blends of (P3HT/P(VDF–TrFE)) poly(3-hexylthiophene) and poly(vinylidene fluoride with trifluoroethylene) due to ferroelectric poling

Wong, Freddy; Perez, Godohaldo; Bonilla, Manuel; Colon-Santana, Juan A.; Zhang, Xin; Sharma, Pankaj; Gruverman, Alexei; Dowben, Peter A.; Rosa, Luis G.

doi:10.1039/c3ra43993c

Cited by 10 publications

(7 citation statements)

References 57 publications

(115 reference statements)

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“…Notably, the g -value of the broad component (2.0031) is more distant from g e (the g -value of the free electron: 2.0023) than that of the narrow component. This larger difference from g e is well explained by the heavy atom effect of spin–orbit coupling (SOC) by sulfur atoms in thiophene rings because the spin density on the sulfur atom is expected to be larger in the lowest unoccupied molecular orbital (LUMO) than that in the highest occupied molecular orbital (HOMO) in P3HT . We speculate that SOC on the sulfur atom could cause the greater difference from g e and the broadening of spectral line width.…”

Section: Resultsmentioning

confidence: 90%

Electron–Hole Pairs Generated in the Crystalline Phase of Polymer Diodes Studied by Electrically Detected Magnetic Resonance Techniques

Iwamoto¹,

Hayakawa²,

Hatanaka³

et al. 2019

J. Phys. Chem. C

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The properties of electron−hole (e−h) pairs generated in a working poly(3-hexylthiophene) (P3HT) diode are investigated by electrically detected magnetic resonance (EDMR) techniques. The EDMR intensity is shown to increase with increasing density of injected electrons for a given hole density, demonstrating that the EDMR signal arises from an e−h pair. The EDMR spectrum consists of two Gaussian curves, one of which gives a g-value very similar to that of hole carriers, suggesting that the EDMR spectrum is given by the sum of electron spin resonance (ESR) spectra from hole and electron carriers forming e−h pairs. Bias-dependent correlation between carriers and e−h pairs under diode operation is examined directly from independent measurements of near-infrared (NIR) spectroscopy for carriers and EDMR for e−h pairs. When the bias is increased to above a threshold, the EDMR signal is strongly reduced despite a gradual increase in the NIR signals, providing evidence that the e−h pairs are dissociated by an electric field in the bias region. Because of this property of the pair, the correlation between the carriers and e−h pairs inside the diode changes depending on the bias magnitude: the carriers and e−h pairs coexist or only the carriers exist. The e−h pair is presumed to be formed across different lamellae because of the crystalline phase of the P3HT film. Although the intensity of the EDMR signal from the interlamellar e−h pair is small, the intensity increases substantially when the sample is exposed to air, suggesting the formation of a magnetoreactive species that incorporates oxygen.

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Section: Resultsmentioning

confidence: 90%

Electron–Hole Pairs Generated in the Crystalline Phase of Polymer Diodes Studied by Electrically Detected Magnetic Resonance Techniques

Iwamoto¹,

Hayakawa²,

Hatanaka³

et al. 2019

J. Phys. Chem. C

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“…The difference of g -factors for the hole and electron in P3HT has been recently reported with the density functional theory (DFT) calculation . The DFT calculations for P3HT indicate that the electron density on the sulfur atoms of the thiophene groups of the LUMO is greater than that on the sulfur atoms of the thiophenes of the HOMO. − The nonvanishing electron density on the sulfur atoms associated with the LUMO results in the electron g -factor being larger than the hole g -factor. No clear EDMR spectrum was observed under dark conditions even at E = 1.17 × 10 5 V·cm –1 , where appreciable hole current (0.283 μA) flowed across the P3HT film (Figure S2).…”

Section: Resultsmentioning

confidence: 99%

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Wakikawa

Ikoma

2020

J. Phys. Chem. C

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Using electrically and capacitively detected magnetic resonance (EDMR and CDMR) techniques, we clarified recombination in regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) films, which is an important elementary process for photoconduction. The modulation frequency dependences of the EDMR and CDMR reveal the coexistence of two types of electron− hole (e−h) pairs with different lifetimes in the device fabricated with a Schottky contact between P3HT and an Al electrode. The short-lived e−h pair is a precursor of the recombination of free carriers in the bulk P3HT. The long-lived e−h pair is involved in the recombination of space charges in the Schottky junction region, which leads to an enhancement of the photocurrent.

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“…Because holes are transported through HOMOs, the relative orientation between the HOMOs of PT and perovskite as a result of different PT orientations becomes the key for solar cell performance. According to previously studied HOMOs of both P3HT and lead iodine-based perovskite, , they would overlap better with a lying down PT thiophene backbone orientation. Therefore, an edge-on thiophene backbone would lead to a greater offset of HOMO–HOMO between perovskite and PTs.…”

Section: Resultsmentioning

confidence: 99%

Effect of Interfacial Molecular Orientation on Power Conversion Efficiency of Perovskite Solar Cells

et al. 2017

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A wide variety of charge carrier dynamics, such as transport, separation, and extraction, occur at the interfaces of planar heterojunction solar cells. Such factors can affect the overall device performance. Therefore, understanding the buried interfacial molecular structure in various devices and the correlation between interfacial structure and function has become increasingly important. Current characterization techniques for thin films such as X-ray diffraction, cross section scanning electronmicroscopy, and UV-visible absorption spectroscopy are unable to provide the needed molecular structural information at buried interfaces. In this study, by controlling the structure of the hole transport layer (HTL) in a perovskite solar cell and applying a surface/interface-sensitive nonlinear vibrational spectroscopic technique (sum frequency generation vibrational spectroscopy (SFG)), we successfully probed the molecular structure at the buried interface and correlated its structural characteristics to solar cell performance. Here, an edge-on (normal to the interface) polythiophene (PT) interfacial molecular orientation at the buried perovskite (photoactive layer)/PT (HTL) interface showed more than two times the power conversion efficiency (PCE) of a lying down (tangential) PT interfacial orientation. The difference in interfacial molecular structure was achieved by altering the alkyl side chain length of the PT derivatives, where PT with a shorter alkyl side chain showed an edge-on interfacial orientation with a higher PCE than that of PT with a longer alkyl side chain. With similar band gap alignment and bulk structure within the PT layer, it is believed that the interfacial molecular structural variation (i.e., the orientation difference) of the various PT derivatives is the underlying cause of the difference in perovskite solar cell PCE.

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Changing molecular band offsets in polymer blends of (P3HT/P(VDF–TrFE)) poly(3-hexylthiophene) and poly(vinylidene fluoride with trifluoroethylene) due to ferroelectric poling

Cited by 10 publications

References 57 publications

Electron–Hole Pairs Generated in the Crystalline Phase of Polymer Diodes Studied by Electrically Detected Magnetic Resonance Techniques

Electron–Hole Pairs Generated in the Crystalline Phase of Polymer Diodes Studied by Electrically Detected Magnetic Resonance Techniques

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Effect of Interfacial Molecular Orientation on Power Conversion Efficiency of Perovskite Solar Cells

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