Surface photovoltage of thin organic films studied by modulated photoelectron emission

Teich, Sebastian; Grafström, S.; Eng, Lukas M.

doi:10.1016/j.susc.2004.01.007

Cited by 9 publications

(7 citation statements)

References 19 publications

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“…On the contrary, some other OPV cells did not exhibit such a relationship (31–33). Although the origins of V OC have been often discussed on the basis of the electronic structures at the D/A interface under a dark condition, the electronic states of organic films in the vicinity of their interface, such as built-in potential ( V bi ), under light irradiation were reported to be changed by photo-generated carriers (electrons and holes) (34, 35). For example, the surface potential of a dimethylquinquethiophene (DM5T) film on a Platinum (Pt) substrate decreases from 190 to 20 mV upon photoirradiation, because photo-generated holes are moved to the Pt substrate by a local electrical field at the interface (34).…”

Section: The Origin Of Open-circuit Voltage For Zn(oep)/c60 Heteromentioning

confidence: 99%

Basic aspects for improving the energy conversion efficiency of hetero-junction organic photovoltaic cells

Ryuzaki

Onoe

2013

Nano Reviews

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Hetero-junction organic photovoltaic (OPV) cells consisting of donor (D) and acceptor (A) layers have been regarded as next-generation PV cells, because of their fascinating advantages, such as lightweight, low fabrication cost, resource free, and flexibility, when compared to those of conventional PV cells based on silicon and semiconductor compounds. However, the power conversion efficiency (η) of the OPV cells has been still around 8%, though more than 10% efficiency has been required for their practical use. To fully optimize these OPV cells, it is necessary that the low mobility of carriers/excitons in the OPV cells and the open circuit voltage (V OC), of which origin has not been understood well, should be improved. In this review, we address an improvement of the mobility of carriers/excitons by controlling the crystal structure of a donor layer and address how to increase the V OC for zinc octaethylporphyrin [Zn(OEP)]/C60 hetero-junction OPV cells [ITO/Zn(OEP)/C60/Al]. It was found that crystallization of Zn(OEP) films increases the number of inter-molecular charge transfer (IMCT) excitons and enlarges the mobility of carriers and IMCT excitons, thus significantly improving the external quantum efficiency (EQE) under illumination of the photoabsorption band due to the IMCT excitons. Conversely, charge accumulation of photo-generated carriers in the vicinity of the donor/acceptor (D/A) interface was found to play a key role in determining the V OC for the OPV cells.

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Section: The Origin Of Open-circuit Voltage For Zn(oep)/c60 Heteromentioning

confidence: 99%

Basic aspects for improving the energy conversion efficiency of hetero-junction organic photovoltaic cells

Ryuzaki

Onoe

2013

Nano Reviews

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“…[10]). This results in a certain kineticenergy distribution of the emitted photoelectrons, which reflects the binding energies of the respective core levels.…”

Section: Xps-based Surface Photovoltage Spectroscopy (X-sps)mentioning

confidence: 99%

“…To achieve a better SPV resolution, one would have to work with modulated excitation and phasesensitive detection [10]. This would result in a lower excitation intensity and thus a lower SPV.…”

Section: X-spsmentioning

confidence: 99%

“…Especially for the study of high-bandgap materials, to which perovskite oxides such as the titanates can be assigned, SPS is superior to other spectroscopy methods [5][6][7]. The implementation of SPS may be carried out in several ways such as the photoassisted Kelvin probe technique, the capacitive detection of the displacement current in a metal-insulator-semiconductor (MIS) structure under chopped illumination [9], and photoelectron spectroscopy (either X-ray photoelectron spectroscopy (XPS) or ultraviolet photoelectron spectroscopy (UPS)) with additional optical excitation [10].…”

Section: Introductionmentioning

confidence: 99%

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Surface Photovoltage Spectroscopy for the Investigation of Perovskite Oxide Interfaces

et al. 2005

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In the present study, we comparatively investigate the distribution of electronic interface states of three different perovskite oxide interfaces, formed by epitaxial thin films of La0.7Sr0.3MnO3 (LSMO), La0.7Ca0.3MnO3 (LCMO), and La0.7Ce0.3MnO3 (LCeMO) on SrTiO3(100) substrates, in the as-prepared state as well as after an annealing procedure. We find that annealing significantly reduces the number and density of interface trap states. Two different experimental realizations of the surface photovoltage spectroscopy (SPS) technique were employed: an approach based on Xray photoelectron spectroscopy (XPS), as well as a capacitive method. The advantages and limitations of both methods are critically discussed. 0902-T07-05.1 Mater. Res. Soc. Symp. Proc. Vol. 902E

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“…(1) and (2), in order to increase the energy conversion efficiency (η) it is necessary to increase I SC and V OC . Previous studies reported that the I SC is limited by the small exciton diffusion length (10 to 30 nm) (step 2) [2] and the low carrier mobility (step 4) due to a high resistance of organic films (e.g., in the case of C 60 , 10 8 to 10 14 Ωcm [3]). In previous studies [4,5], it was shown that the I SC can be increased by increasing the exciton diffusion length and/or the carrier mobility, and the number of excitons by adjusting the molecular orientation in the organic film and by increasing the area of the D/A interface surface, respectively.…”

Section: Introductionmentioning

confidence: 99%

Photo‐generated Carrier Dynamics in the Vicinity of the Donor/Acceptor Interface of Organic Solar Cells

Ryuzaki

Onoe

2013

Elect Comm in Japan

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SUMMARYChange in electronic states before and after photo-irradiation at a Donor/Acceptor (D/A) interface in organic solar cells consisting of zinc-porphyrin and fullerene films has been examined using in situ impedance spectroscopy (IS), which makes it possible to non-destructively measure a built-in potential (V bi ) of both D and A films at the D/A interface. The accumulation of photo-generated carriers in the vicinity of the D/A interface was found to increase the V bi of both D [Zn(OEP)] and A [C 60 ] films at the interface. In addition, it was noted that the sum of V bi obtained on photo-irradiation was in good agreement with the open-circuit voltage (V OC ), of which the origin is still unsolved for organic solar cells. Thus, the charge accumulation of photogenerated carriers in the vicinity of the D/A interface plays a key role in determining V OC .

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Surface photovoltage of thin organic films studied by modulated photoelectron emission

Cited by 9 publications

References 19 publications

Basic aspects for improving the energy conversion efficiency of hetero-junction organic photovoltaic cells

Basic aspects for improving the energy conversion efficiency of hetero-junction organic photovoltaic cells

Surface Photovoltage Spectroscopy for the Investigation of Perovskite Oxide Interfaces

Photo‐generated Carrier Dynamics in the Vicinity of the Donor/Acceptor Interface of Organic Solar Cells

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