Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV18)
Publication date: 21st February 2018
To construct efficient solar cells, the ionization potential (IP) and work function (WF) of constituent materials are one of the most important properties to achieve a good energy level matching. We developed a photoemission yield spectrometer (Photoemission Yield Spectroscopy in Air; PYSA, Riken Keiki Co. Ltd.) to measure WF and/or IP in the air. The PYSA includes a specially designed detector, the “open counter” [1-3], enabling us to detect low energy photoelectrons emitted form materials under atmospheric conditions. Unlike conventional photoelectron spectroscopies of XPS and UPS, the PYSA can carry out a non-vacuum measurement with a high energy-resolution and low photo-excitation energies. A non-vacuum measurement is very suitable for organic semiconductors in powdered or liquid states. Moreover, low energy excitation can ionize electrons at energy levels about the highest occupied molecular orbital (HOMO) with a relatively high efficiency, and make the irradiation damages of samples negligible.
In this paper, the electronic properties of raw materials and transparent conductive oxides used for Perovskite and Quantum dots solar cell devices were studied with the PYSA. A PYSA measurement was carried out as follows. UV light emitted from a deuterium lamp were dispersed by a monochromator and focused on a sample. The photoelectrons emitted from the sample were counted by the open counter. Here, the energies of monochromatized UV photons can be scanned from 4.0 eV to 7.0 eV with an increment of 0.05 eV. When UV photons with energies higher than 6.20 eV are required, most of the air in the monochromator must be replaced with N2 gas to minimize the absorption loss of UV light by air.
Each materials were coated on glass substrates. The IPs of the layers were estimated from an observed photoemission threshold energy. The PYSA is useful to measure such electronic properties.
[1] M. Uda and H. Kirihata, Japanese Patent S55-179922 (1980), 1447157 (1988)
[2] H. Kirihata, and M. Uda, Rev. Sci. Instr. 52, 68 (1981).
[3] M. Uda, Jpn. J. Appl. Phys. 24, 284 (1985)
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