Contributed Speaker
Dmitrii Sychev
Visualization of the charge transfer processes in the tapered cross section of the operating solar cell device by means of KPFM
Dmitrii Sychev1, Alina Senina2, Fabian Paulus2,3, Ilka Hermes1
1Leibniz Institute of Polymer Research Dresden e.V., Hohe Str. 6, 01069 Dresden, Germany
2Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Helmholtzstraße 20, 01069 Dresden, Germany.
3Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden,
Helmholtzstraße 18, 01069 Dresden, Germany
Using the sun as an energy source instead of fossil fuel allows a significant reduction of CO2 emissions. The photovoltaic process requires the semiconducting light absorber. In the last decade, metal halide perovskites have conquered the solar cell community due to their astonishing power conversion efficiency (PCE) as an active layer and relatively easy and cheap synthesis. However, metal halide perovskites are highly susceptible to water and oxygen, limiting their application. The use of more stable materials in air could be a promising step towards commercialization. In this regard, quantum dots (QDs), which are semiconductive nanoparticles, open a new perspective. In particular, lead and cadmium-based chalcogenide QDs have been shown to be a promising air-stable substitute for metal halide perovskite materials active layers in perovskite solar cells. However, both lead and cadmium are toxic. Therefore, the fabrication of the devices based on lead- and cadmium-free QDs is of great importance for commercialization. Up until now, such materials have shown lower PCE leaving room for improvement in device architecture and QDs passivation optimization.
To understand the underlying processes of charge separation in the device and to determine the limits of power conversion, the visualization of charge distribution within the layers of the solar cell is crucial. Kelvin probe force microscopy (KPFM) allows the measurement of the surface potential at each point of the tapping mode topography AFM scan, creating a map that shows the (photo-) charging in the different layers of the solar cells. Since the combined thickness of the active and transport layers in perovskite-based or the QDs-based solar cell devices is below 1 µm, it can be helpful to artificially elongate the area of interest via low angle tapered cross-sectioning. Here, we demonstrate the preparation of tapered cross-sections of QDs-based solar cells using a focused ion beam. Heterodyne KPFM imaging of the tapered cross-section visualized active and transport layers distinctly. By illuminating the solar cell we can visualize the impact of each interface on the charge separation.