Charge Accumulation in Organic Solar Cells during Device Operation as Investigated by Electron Spin Resonance

Nagamori, Tatsuya; Marumoto, Kazuhiro

doi:10.7567/jjap.52.05dc13

Cited by 6 publications

(4 citation statements)

References 28 publications

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“…The ESR parameters obtained from this work are listed in Table . The g -factors are consistent with those described in reports of earlier studies; the origins of the ESR signal are positive polarons (or radical cations) in PEDOT doped by PSS. − The treated PEDOT:PSS film in the ITO/treated PEDOT:PSS sample shows an ESR spectrum with g = 2.0029 ± 0.0001 and Δ H pp = 0.57 ± 0.05 mT. The g -factor and Δ H pp are the same as those derived from the as-deposited PEDOT:PSS film.…”

Section: Resultssupporting

confidence: 87%

Open-Circuit-Voltage Improvement Mechanism of Perovskite Solar Cells Revealed by Operando Spin Observation

Kimata,

Yamaguchi,

Gotanda

et al. 2023

ACS Appl. Mater. Interfaces

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Organic-inorganic hybrid perovskite solar cells have attracted much attention as one of the most important next-generation solar cells. The solar-cell performances are known to be changed under operation; however, the root cause of the instability has not yet been understood su ciently. Here, we report improvement mechanism in the open-circuit voltage, V OC , of perovskite solar cells at the initial stage of device operation that were rstly investigated by electron spin resonance (ESR). ESR study reveals reverse electrons transfer at the interface from the perovskite layer to the hole-transport layer not only under dark conditions but also under light irradiation where electrons are subsequently trapped in the hole-transport layer. Thereby, an electron barrier is enhanced at the perovskite/hole-transport-layer interface, improving eld-effect passivation at the interface, and thus the V OC improves. These ndings are crucial for understanding the mechanisms of device performance changes under operation, showing a relation between reverse electrons transfer and performance improvement, which is valuable for the development of further e cient perovskite solar cells.

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Section: Resultssupporting

confidence: 87%

Open-Circuit-Voltage Improvement Mechanism of Perovskite Solar Cells Revealed by Operando Spin Observation

Kimata,

Yamaguchi,

Gotanda

et al. 2023

ACS Appl. Mater. Interfaces

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“…We have previously used IS to investigate inverted PSCs containing metal oxides as electron collection electrodes. − Electron spin resonance (ESR) spectroscopy is also a promising method for the microscopic characterization of charge-accumulation sites. Charge carriers in most organic semiconductors have a spin, which allows the use of ESR to directly observe charge carriers that accumulate during device operation. − The ESR method has been successfully used to determine the microscopic properties of charge-carrier states in organic devices, including spin states and the spatial extent of wave functions in organic materials at device interfaces. We have previously investigated the mechanism of the light-soaking effect that accompanied a short-circuit photocurrent increase in inverted PSCs containing amorphous titanium oxide, using both ESR and IS methods …”

Section: Introductionmentioning

confidence: 99%

Mechanism of Light-Soaking Effect in Inverted Polymer Solar Cells with Open-Circuit Voltage Increase

Kusumi¹,

Fujimori²,

Minami³

et al. 2017

ACS Omega

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In this study, we present novel insights into the light-soaking effect of inverted polymer solar cells (PSCs), where the open-circuit voltage ( V oc ) of the cells improves over time under light irradiation. The effect was investigated by electron spin resonance (ESR) studies of bare indium tin oxide (ITO) and piperazine derivative-modified ITO/regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C 61 butyric acid methyl ester (PCBM) substrates. These results were combined with alternating current impedance spectroscopy (IS) measurements of inverted PSCs based on the above substrates. In ESR experiments with the substrates under white light irradiation, with a UV light component, many P3HT •+ radical cations were observed in the bare-ITO/P3HT:PCBM substrate. The number of radical cations was considerably suppressed in the ITO/P3HT:PCBM substrates with ITO modified by piperazine derivatives. This is because adsorbed oxygen molecules on the ITO acted as acceptor dopants for photoexcited P3HT, and the amount of adsorbed oxygen was decreased by modifying the ITO with piperazine derivatives. In IS measurements of the inverted PSCs under white light irradiation, a decrease in the electric capacitance (CPE2) of an electric double layer formed at the ITO/P3HT:PCBM interface was observed. A strong correlation was observed between the decrease of CPE2 and the increase of V oc . From these results, the light-soaking behavior was attributed to the removal of an electron injection barrier formed between ITO and PCBM, under white light irradiation.

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“…The ESR method has successfully been used to determine the microscopic properties of charge-carrier states in organic devices, including spin states and the spatial extent of wave functions in organic materials at device interfaces. We have previously investigated the accumulation of photogenerated charge carriers in conventional polymer solar cells under typical device operating conditions using the ESR method. − …”

Section: Introductionmentioning

confidence: 99%

Mechanistic Investigation into the Light Soaking Effect Observed in Inverted Polymer Solar Cells Containing Chemical Bath Deposited Titanium Oxide

Kawamata¹,

Yano²,

Yamaguchi³

et al. 2015

J. Phys. Chem. C

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In the glass-indium tin oxide (ITO) / titanium oxide (TiO x ) / regioregular poly(3-hexylthiophene) (P3HT) : [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) / poly(3,4-ethylenedioxylenethiophene) : poly(4-styrene sulfonic acid) (PEDOT:PSS) / Au cell (TiO x cell), which contains amorphous titanium oxide prepared by chemical bath deposition and dried at 150 °C, a light soaking effect has been observed upon irradiation with white light.In contrast, in ITO / titanium oxide (TiO 2 ) / P3HT:PCBM / PEDOT:PSS / Au cell (TiO 2 cell), which contains anatase titanium oxide prepared by heat treatment at 450 °C, the maximum power conversion efficiency was obtained just after irradiation with white light. The number of P3HT + cation radicals in the quartz-ITO/TiO x and TiO 2 /P3HT:PCBM substrates was estimated by ESR measurements at room temperature upon irradiation with white light. They increased gradually with an increase in irradiation time for the TiO x substrate, but increased only slightly just after light irradiation for the TiO 2 substrate. Upon irradiation with UV-cut light, the performance of the TiO x cell was inferior to that of the TiO 2 cell. This could be related to the resistances of the P3HT:PCBM layers which were estimated by alternating-current impedance spectroscopy. The resistance of the P3HT:PCBM layer in the TiO x cell was much larger than that in the TiO 2 cell, though the difference between the two cells was merely heat treatment temperature of titanium oxide films using as electron collection layers. That is, the concentration of photocarriers in the P3HT:PCBM of the TiO x 2 cell was significantly less than that in the P3HT:PCBM of the TiO 2 cell. From these experimental results, the light soaking effect could be reasonably explained by assuming the existence of charge recombination centers in the TiO x near the TiO x /P3HT:PCBM interface.

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Charge Accumulation in Organic Solar Cells during Device Operation as Investigated by Electron Spin Resonance

Cited by 6 publications

References 28 publications

Open-Circuit-Voltage Improvement Mechanism of Perovskite Solar Cells Revealed by Operando Spin Observation

Open-Circuit-Voltage Improvement Mechanism of Perovskite Solar Cells Revealed by Operando Spin Observation

Mechanism of Light-Soaking Effect in Inverted Polymer Solar Cells with Open-Circuit Voltage Increase

Mechanistic Investigation into the Light Soaking Effect Observed in Inverted Polymer Solar Cells Containing Chemical Bath Deposited Titanium Oxide

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