Accessing the band alignment in high efficiency Cu(ln,Ga)(Se,S)_2 (CIGSSe) solar cells with an ln_xS_y:Na buffer based on temperature dependent measurements and simulations

摘要

We present a one-dimensional simulation model for high efficiency Cu(In,Ga)(Se,S)(2) solar cells with a novel band alignment at the hetero-junction. The simulation study is based on new findings about the doping concentration of the InxSy: Na buffer and i-ZnO layers as well as comprehensive solar cell characterization by means of capacitance, current voltage, and external quantum efficiency measurements. The simulation results show good agreement with the experimental data over a broad temperature range, suggesting the simulation model with an interface-near region (INR) of approximately 100nm around the buffer/absorber interface that is of great importance for the solar cell performance. The INR exhibits an inhomogeneous doping and defect density profile as well as interface traps at the i-layer/buffer and buffer/absorber interfaces. These crucial parameters could be accessed via their opposing behavior on the simulative reconstruction of different measurement characteristics. In this work, we emphasize the necessity to reconstruct the results of a set of experimental methods by means of simulation to find the most appropriate model for the solar cell. Lowly doped buffer and intrinsic window layers in combination with a high space charge at the front of the absorber lead to a novel band alignment in the simulated band structure of the solar cell. The presented insights may guide the strategy of further solar cell optimization including (alkali-) post deposition treatments. Published by AIP Publishing.