Ing. Mgr. Neda Neykova, Ph.D.
The laboratory has always been focused on thin-film materials for photovoltaic cells, especially by the methods of measuring the absorption edge - either by the method of photothermal deflection spectroscopy (PDS), by measuring the photocurrent or by photo-luminescence. Especially photocurrent measurement has a tradition in the group since the 1980s, when Dr. Milan Vaněček introduced the method of constant photocurrent CPM (Constant Photocurrent Method), which he replaced at the turn of the millennium with the method FTPS (Fourier-Transform Photocurrent Spectroscopy) using Fourier approach. These methods have become widely known in the world. Other methods available in our group include FTIR ATR (attenuated total reflectance) and FTIR Raman spectroscopy. The basic approach is to study the absorption edge and sub-bandgap absorption, which gives information about the semiconductor arrangement and the concentration of deep traps. This study requires high sensitivity of measurement, which is achievable by the PDS and FTPS methods. The research was initially focused on thin-film amorphous and microcrystalline hydrogenated silicon, which acts as an absorber in a solar cell. Later, semiconductors acting as transparent electrodes, in particular based on ZnO or diamond, have become of interest. These materials can also be nanostructured. The group has a facility for the preparation of these nanostructures and even patented a solar cell with a nanostructured ZnO electrode. In addition to evaluating low absorption, PDS and FTPS can be used to evaluate spectral optical properties in a wide spectral range. It then allows, for example, to optically simulate the effects on a solar cell performance, especially by including the optical scattering – caused by nanostructures. Recently, new material - hybrid organic-inorganic perovskite CH3NH3PbI3 - has come to the forefront of photovoltaic technology. Since 2014, when we first measured the steepness of the absorption edge of this material and showed a link with its quality [S. De Wolf, J. Holovsky, et al., J. Phys. Chem. Lett. 2014, 5, 1035.], this material has become a new subject of interest for this group. Crucial is the cooperation with a group in Neuchatel, Switzerland and SOL-MAT group at the Faculty of Electrical Engineering of the Czech Technical University in Prague.