Topic 5 min read

Scanning Probes & Photovoltaic Research

Latest updated: October 8, 2024

The exponential growth in the use of photovoltaics, and improvement in the technology’s performance, has led it to become a familiar sight on many buildings. Novel developments in photovoltaics are therefore of great interest. Scanning probe electrochemistry has already been used to help answer a number of questions relating to photovoltaics as outlined in the table below.

Question	Technique	Information Measured	Example
What is the work function of the photovoltaic materials?	SKP	In SKP the probe and sample are electrically connected. The differing work functions of the probe and the sample cause a flow of charge from one material to the other resulting in the equilibration of the Fermi levels. The result is the development of a surface charge, and parallel plate capacitor. The difference in the potential of between the probe and the sample are measured during SKP. By first calibrating the probe it is then possible to determine the local work function of the sample in a non-contact, non-destructive manner.	X. Liu et al., Journal of Materials Chemistry A 1 (2013) 10703 X. Liu et al., Physical Chemistry Chemical Physics 17 (2015) 17041
How do different sensitizers and electrolytes for Dye Sensitized Solar Cells (DSSC) compare?	SECM	Illumination causes charge to be present at the DSSC electrode surface. This charge in turn leads to increased electron transfer at the UltraMicroElectrode (UME) SECM probe diffusion layer. Increased electron transfer causes a larger current magnitude to be measured at the UME. Sensitizers and electrolytes which produce a more active DSSC will show increased current magnitude. The probe can be scanned in x, and y to investigate local effects.	C. J. Martin et al., Journal of Physical Chemistry C 118 (2014) 16912-16918 C. J. Martin et al., Electrochimica Acta 119 (2014) 86– 91
How does the half-life for stabilization compare for different sensitizer-electrolyte systems for DSSCs?	SECM	The half-life for stabilization of the sensitizer-electrolyte system can be measured by bringing the SECM probe to the region of highest current magnitude above the DSSC electrode surface under dark conditions. The probe can then be biased in a chronoamperometry measurement to follow current change with changing illumination. After the system is illuminated the current measured will increase, and the time length for the current to reach steady state noted to determine the half-life for stabilization.	C. J. Martin et al., Journal of Physical Chemistry C 118 (2014) 16912-16918
How does the electrical conductivity of the donor/acceptor material locally change during doping?	SDC	SDC confines the electrochemical cell to the area under the droplet, therefore it can be used for local electrochemical investigations. Electrical conductivity of a donor/acceptor material can be locally investigated by using SDC to perform local Electrochemical Impedance Spectroscopy (EIS) at different potential biases to induce the electrochemical doping. Fitting the resulting EIS spectra allows changes in the resistance of the donor/acceptor to be determined and plotted. It is expected that the fitted EIS will show a decrease in resistance as the potential is changed to induce doping. An increase in resistance may ultimately occur reflecting breakdown of the acceptor/donor material.	J. Gasiorowski et al., Electrochimica Acta 113 (2013) 834– 839
Can high throughput of solar cell material libraries be performed?	Modified SECM	The SECM measurement can be modified so that the conventional UME probe is replaced with an optical fiber to localize the substrate illumination inducing photoelectrocatalytic reactions locally. In this case the sample is connected to a potentiostat and the substrate current is measured as the optical fiber probe is moved over the material library. When the probe illuminates a highly active point an increase in current will be measured.	D. Yuan et al., ACS Applied Materials & Interfaces 8 (2016) 18150-18156

Glossary:

Scanning ElectroChemical Microscopy (SECM): Measurement of local electrochemical activity of a sample with chemical selectivity. The local impedance of a sample can also be measured.
Localized Electrochemical Impedance Spectroscopy (LEIS): Measurement of local impedance differences and point-by-point Electrochemical Impedance Spectroscopy
Scanning Kelvin Probe (SKP): Local non-contact measurement of sample work function. Topography can also be measured.
Scanning Vibrating Electrode Technique (SVET): Measurement of local current distribution of a sample in electrolyte. Also known as Vibrating Probe.
Scanning Droplet Cell (SDC): Local electrochemical and impedance measurements of a sample within a droplet.
Optical Surface Profiler (OSP): Non-contact measurement of local sample topography.