Sample preparation for scanning Kelvin probe microscopy studies on cross sections of organic solar cells

AbstractWe have investigated different methods for preparing CdTe/CdS cross sections for electrical measurements, including the following: cleaving; using GaAs substrates; and sandwiching the structure between the substrate and a glass slide, and polishing with diamond discs and alumina suspension. The latter method proved to be the most reliable, with a success rate of over 90%.We investigated cross sections of CdTe/CdS samples with scanning Kelvin probe microscopy (SKPM) using two different methods: applying the alternate bias with a frequency equal to 18.5 kHz, or equal to the frequency of the second cantilever resonance peak. The results showed that using the second resonance frequency produced a smoother signal, allowing the calculation of the electric field inside the device using just the raw SKPM data.We were able to measure the distribution of the electrical potential inside working devices. Then, by taking the first derivative of the potential, we calculated the electric field and determined the location of the p-n junction.

Download Full-text

Electrical properties of CdTe/CdS AND CdTe/SnO2 solar cells studied with scanning kelvin probe microscopy

2010 35th IEEE Photovoltaic Specialists Conference ◽

10.1109/pvsc.2010.5616694 ◽

2010 ◽

Author(s):

H.R. Moutinho ◽

R.G. Dhere ◽

C.-S. Jiang ◽

D.S. Albin ◽

M.M. Al-Jassim

Keyword(s):

Solar Cells ◽

Electrical Properties ◽

Kelvin Probe ◽

Probe Microscopy ◽

Kelvin Probe Microscopy ◽

Scanning Kelvin Probe

Download Full-text

Measurement of built-in electrical potential in III–V solar cells by scanning Kelvin probe microscopy

Journal of Applied Physics ◽

10.1063/1.1573736 ◽

2003 ◽

Vol 93 (12) ◽

pp. 10035-10040 ◽

Cited By ~ 54

Author(s):

Chun-Sheng Jiang ◽

H. R. Moutinho ◽

D. J. Friedman ◽

J. F. Geisz ◽

M. M. Al-Jassim

Keyword(s):

Solar Cells ◽

Electrical Potential ◽

Kelvin Probe ◽

Probe Microscopy ◽

Kelvin Probe Microscopy ◽

Scanning Kelvin Probe

Download Full-text

Influence of Surface Preparation on Scanning Kelvin Probe Microscopy and Electron Backscatter Diffraction Analysis of Cross Sections of CdTe/CdS Solar Cells

MRS Proceedings ◽

10.1557/opl.2011.1057 ◽

2011 ◽

Vol 1324 ◽

Cited By ~ 2

Author(s):

H.R. Moutinho ◽

R.G. Dhere ◽

C.-S. Jiang ◽

M.M. Al-Jassim

Keyword(s):

Solar Cells ◽

Cross Section ◽

Cross Sections ◽

Electron Backscatter Diffraction ◽

Ion Beam ◽

Kelvin Probe ◽

Probe Microscopy ◽

Kelvin Probe Microscopy ◽

Electron Backscatter ◽

Backscatter Diffraction

ABSTRACTElectron backscatter diffraction (EBSD) provides information on the crystallographic structure of a sample, while scanning Kelvin probe microscopy (SKPM) provides information on its electrical properties. The advantage of these techniques is their high spatial resolution, which cannot be attained with any other techniques. However, because these techniques analyze the top layers of the sample, surface or cross section features directly influence the results of the measurements, and sample preparation is a main step in the analysis.In this work we investigated different methods to prepare cross sections of CdTe/CdS solar cells for EBSD and SKPM analyses. We observed that procedures used to prepare surfaces for EBSD are not suitable to prepare cross sections, and we were able to develop a process using polishing and ion-beam milling. This process resulted in very good results and allowed us to reveal important aspects of the cross section of the CdTe films. For SKPM, polishing and a light ion-beam milling resulted in cross sections that provided good data. We were able to observe the depletion region on the CdTe film and the p-n junction as well as the interdiffusion layer between CdTe and CdS. However, preparing good-quality cross sections for SKPM is not a reproducible process, and artifacts are often observed.

Download Full-text

Measurement of the Electric Potential on Amorphous Silicon and Amorphous Silicon Germanium Alloy Thin-Film Solar Cells by Scanning Kelvin Probe Microscopy

MRS Proceedings ◽

10.1557/proc-808-a9.42 ◽

2004 ◽

Vol 808 ◽

Cited By ~ 4

Author(s):

C.-S. Jiang ◽

H. R. Moutinho ◽

Q. Wang ◽

M. M. Al-Jassim ◽

B. Yan ◽

...

Keyword(s):

Solar Cells ◽

Electric Field ◽

Amorphous Silicon ◽

Alloy Thin Film ◽

Surface Charges ◽

Kelvin Probe ◽

Potential Measurement ◽

Probe Microscopy ◽

Kelvin Probe Microscopy ◽

Scanning Kelvin Probe

ABSTRACTWe report on direct measurements of surface potentials on cross sections of a-Si:H and a-SiGe:H n-i-p solar cells using scanning Kelvin probe microscopy. External bias voltage (Vb)induced changes in the electric field distributions in the i layer were further deduced by taking the derivative of the Vb-induced potential changes. This procedure avoids the effect of surface charges or surface Fermi-level pinning on the potential measurement. We found that the electric field does not distribute uniformly through the i layer of a-Si:H cells, but it is stronger in the regions near the n and p layers than in the middle of the i layer. The non-uniformity is reduced by incorporating buffer layers at the n/i and i/p interfaces in the a-Si:H solar cells. For a-SiGe:H solar cells, the electric field at the p side of the i layer is much stronger than at the n side and the middle. The non-uniformity becomes more severe when a profiled Ge content is incorporated with a high Ge content on the p side. We speculate that the increase in defect density with increasing of Ge content causes charge accumulation at the i/p interface.

Download Full-text