Electrical, optical characterization and degradation of Cu(InGa)Se2 devices with fluorine-doped tin oxide back contact

In this letter, we present a complete electrical and optical study of the characteristics and degradation of Cu(InGa)Se (CIGS) solar cells with Florine-doped Tin Oxide (FTO). This is an alternative structure of CIGS solar cell, that is fundamental for the development of bifacial or tandem devices. In the first part of this paper, we report on the electro-optical properties of the devices, based on the results obtained by a set of characterization techniques, including external and internal quantum efficiency (EQE/IQE) and current-voltage (I-V). In addition, the temperature coefficient of the cells is evaluated based on the method proposed in the standard EN 60891: results indicate a very good stability of the short circuit current with temperature, and a temperature coefficient of the open circuit voltage of -1.8 × 10 V/°C, which is slightly lower than what detected in silicon cells. In the last part of the paper, we present the results of a forward current stress experiment, to demonstrate the existence of metastable conductive defects in the crystalline structure of the material, through the analysis of spatial-resolved electroluminescence data.