Evidence of deep defects in CIGSe solar cells from DLTS trap filling study

Deep Level Transient Spectroscopy (DLTS) is often used to identify and quantify defects in semiconductors. In the DLTS spectrum of CIGS (CuInGaSe2) solar cells generally two types of signals are observed : one for which the capacitance transients are measured well below room temperature (RT) labeled N1, and a second corresponding to transients measured close to RT, N2. We have recently shown that the N1 signal can be related to an non-ideal contact in the solar cell. In this work the N2 signal was investigated using isothermal DLTS (capacitance transients at constant voltage) and isothermal constant-capacitance DLTS (CC-DLTS, voltage transients at constant capacitance) experiments at RT. In CC-DLTS a non-exponential factor in the transients due to high trap concentrations is avoided. The effect of filling pulse duration (tp) on the N2 signal is studied here in detail. Both the DLTS and CC-DLTS methods point to an anomalous filling behavior. From a certain tp onwards a peak appears that shifts towards larger emission time as tp increases. The relation between these results and the energy level diagram of the metastable In-on-Cu antisite defect is discussed. DLTS experiments with variation of tp may help to understand the nature of the metastable defects causing the N2 signal

Influence of an Sb doping layer in CIGS thin-film solar cells: a photoluminescence study

Sb doping of Cu(In,Ga)Se2 (CIGS) solar cells has been reported to exhibit a positive effect on the morphology of the absorber layer, offering a possibility to lower manufacturing cost by lowering the annealing temperatures during the CIGS deposition. In this work electron microscopy, energy-dispersive x-ray spectroscopy and photoluminescence experiments have been performed on cells deposited on soda-lime glass substrates, adding a thin Sb layer onto the Mo back contact prior to the CIGS absorber deposition. The defect structure of CIGS solar cells doped with Sb in this way has been investigated and is compared with that of undoped reference cells. The influence of substrate temperature during absorber growth has also been evaluated. For all samples the photoluminescence results can be explained by considering three donor–acceptor pair recombination processes involving the same defect pairs

Assignment of capacitance spectroscopy signals of CIGS solar cells to effects of non-ohmic contacts

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