Showing papers by "Florian Werner published in 2019"
TL;DR: Spindler et al. as discussed by the authors proposed a comprehensive model of the electronic defects in Cu(In,Ga)Se2 based on experiments and theory, and the consequences for solar cell efficiency are discussed.
Abstract: Author(s): Spindler, C; Babbe, F; Wolter, MH; Ehre, F; Santhosh, K; Hilgert, P; Werner, F; Siebentritt, S | Abstract: The electronic defects in any semiconductor play a decisive role for the usability of this material in an optoelectronic device. Electronic defects determine the doping level as well as the recombination centers of a solar cell absorber. Cu(In,Ga)Se2 is used in thin-film solar cells with high and stable efficiencies. The electronic defects in this class of materials have been studied experimentally by photoluminescence, admittance, and photocurrent spectroscopies for many decades now. The literature results are summarized and compared to new results by photoluminescence of deep defects. These observations are related to other experimental methods that investigate the physicochemical structure of defects. To finally assign the electronic defect signatures to actual physicochemical defects, a comparison with theoretical predictions is necessary. In recent years the accuracy of these calculations has greatly improved by the use of hybrid functionals. A comprehensive model of the electronic defects in Cu(In,Ga)Se2 is proposed based on experiments and theory. The consequences for solar cell efficiency are discussed.
50 citations
TL;DR: In this article, the authors reveal the root cause of the challenge in the interface of Cu-rich solar cells in terms of a Se-related defect with an activation energy of $200.
Abstract: Thin-film solar cells consist of several layers. The interfaces between these layers can provide critical recombination paths and consequently play a vital role in the efficiency of the solar cell. One of the main challenges for polycrystalline semiconductor absorber materials is the absorber-buffer interface. The $\mathrm{Cu}(\mathrm{In},\mathrm{Ga})\mathrm{S}{\mathrm{e}}_{2}$ system is particularly interesting in this context, since Cu-rich absorbers are dominated by recombination at the interface, while Cu-poor ones are not. This paper unveils the root cause of the challenge in the interface of Cu-rich solar cells in terms of a Se-related defect with an activation energy of $200\ifmmode\pm\else\textpm\fi{}20\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$. This defect causes interface recombination and is responsible for the deficiency of open-circuit voltage in Cu-rich cells. Moreover, this paper demonstrates that the origin of this defect is due to the etching step necessary to remove secondary phases. Postdeposition surface treatments or modified buffer layers are shown to passivate this defect, to reduce interface recombination, and to increase the efficiency.
32 citations
TL;DR: Werner et al. as mentioned in this paper demonstrate how to assess electrical measurements of thin-film devices and develop a range of criteria that allow to estimate whether deep defects could consistently explain a given capacitance measurement.
Abstract: Author(s): Werner, F; Babbe, F; Elanzeery, H; Siebentritt, S | Abstract: Thermal admittance spectroscopy and capacitance-voltage measurements are well established techniques to study recombination-active deep defect levels and determine the shallow dopant concentration in photovoltaic absorbers. Applied to thin-film solar cells or any device stack consisting of multiple layers, interpretation of these capacitance-based techniques is ambiguous at best. We demonstrate how to assess electrical measurements of thin-film devices and develop a range of criteria that allow to estimate whether deep defects could consistently explain a given capacitance measurement. We show that a broad parameter space, achieved by exploiting bias voltage, time, and illumination as additional experimental parameters in admittance spectroscopy, helps to distinguish between deep defects and capacitive contributions from transport barriers or additional layers in the device stack. On the example of Cu(In,Ga)Se2 thin-film solar cells, we show that slow trap states are indeed present but cannot be resolved in typical admittance spectra. We explain the common N1 signature by the presence of a capacitive barrier layer and show that the shallow net dopant concentration is not distributed uniformly within the depth of the absorber.
8 citations
25 Oct 2019
TL;DR: In this paper, the straightforward synthesis of ultrathin low dielectric constant insulating polymer layers from four cyclic organosilicon monomers (i.e., two organocyclosiloxanes and two OCLs) was presented.
Abstract: The straightforward synthesis of ultrathin low dielectric constant insulating polymer layers from four cyclic organosilicon monomers (i.e., two organocyclosiloxanes and two organocyclosilazanes) by...
6 citations