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)Se 2 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)Se 2 is proposed based on experiments and theory. The consequences for solar cell efficiency are discussed.

Thin‐film Cu(In,Ga)Se2 solar cells reach power conversion efficiencies exceeding 23% and nonradiative recombination in the bulk is reported to limit device performance. The diode factor has not received much attention, although it limits the fill factor, and therefore the efficiency, for state‐of‐the‐art solar cells. Herein, the diode factor of Cu(In,Ga)Se2 absorbers, measured by photoluminescence spectroscopy, and of solar cells, measured by current–voltage and capacitance–voltage characteristics, are compared, supported by simulations using rate equations of generation and recombination. It is found that the diode factor is already increased in the neutral zone of the absorber due to metastable defects, such as the VSe–VCu defect found in Cu(In,Ga)Se2, because of an increased net acceptor density upon minority‐carrier injection. The metastable and persistent increase of the net acceptor density has a detrimental effect on the device performance. Diode factors of 1 and efficiencies exceeding 24% are expected when, in current state‐of‐the‐art Cu(In,Ga)Se2 solar cells, the formation of metastable defects is suppressed.

Ce-doped SiO x N y films are deposited by magnetron reactive sputtering from a CeO 2 target under nitrogen reactive gas atmosphere. Visible photoluminescence measurements regarding the nitrogen gas flow reveal a large emission band centered at 450 nm for a sample deposited under a 2 sccm flow. A special attention is paid to the origin of such an emission at high nitrogen concentration. Different emitting centers are suggested in Ce doped SiO x N y films (e.g. band tails, CeO 2 , Ce clusters, Ce 3+ ions), with different activation scenarios to explain the luminescence. X-ray photoelectron spectroscopy (XPS) reveals the exclusive presence of Ce 3+ ions whatever the nitrogen or Ce concentrations, while transmission electron microscopy (TEM) shows no clusters or silicates upon high temperature annealing. With the help of photoluminescence excitation spectroscopy (PLE), a wide excitation range from 250 nm up to 400 nm is revealed and various excitations of Ce 3+ ions are proposed involving direct or indirect mechanisms. Nitrogen concentration plays an important role on Ce 3+ emission by modifying Ce surroundings, reducing the Si phase volume in SiO x N y and causing a nephelauxetic effect. Taking into account the optimized nitrogen growth parameters, the Ce concentration is analyzed as new parameter. Under UV excitation, a strong emission is visible to the naked eye with high Ce 3+ concentration (6 at. %). No saturation of the photoluminescence intensity is observed, confirming again the lack of Ce cluster or silicate phase formation due do the nitrogen presence.