Analysis of electrical properties of CIGSSe and Cd-free buffer CIGSSe solar cells

We investigated the influence of different buffer layers to the electrical parameters (Jsc, Voc, QE and efficiency η) of solar cells. The cells with an In2S3 and a ZnMgO buffer layer were compared with a reference cell with a CdS buffer layer. We performed temperature and light dependent current-voltage measurements, temperature dependent capacitance measurements and quantum efficiency measurements.The cells with In2S3 and ZnMgO buffers differ not too much in Jsc, but they do differ in Voc and their electrical properties — fill factor FF, diode saturation current J0 and efficiency η. They also do differ in their spectral response, both at short and long wavelengths, and in their ideality factor. This indicates a different current transport mechanism. The device simulation program SCAPS is used for further interpretation of the measurements. After exploring the parameters we found an acceptable agreement between simulated and measured J–V and QE(λ) curves. The simulated QE curves fit well over the whole spectrum, except for the CdS buffer cell, where there is an overestimation for the intermediate wavelengths. Because of this the simulated Jsc is higher than the measured one. The simulated Voc agrees well for all cells. For the ZnMgO buffer cell it was necessary to include a buried homo-junction.