Modelling thin film solar cells with graded band gap

This paper discusses how graded absorber structures in CIGS-based solar cell can be studied using the numerical simulation tool SCAPS. A model will be built for an AVANCIS solar cell with double grading which is produced with the laboratory line process. We will first discuss how literature and measurement data should be used to start the buildup of the model and afterwards give an illustration how the model then still has to be optimized. We will draw special attention to the consequences of a graded structure on the model. Moreover, we will show how one can discern the real grading benefit by comparison with a uniform reference model

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