Achievement of 17.9% efficiency in 30x30cm2 Cu(In, Ga)(Se, S)2 solar cell sub-module by sulfurization after selenization with Cd-free buffer

We have achieved 17.9% efficiency in a 30 x 30 cm(2) Cu(In, Ga)(Se, S)(2) solar cell sub-module prepared by selenization and sulfurization processes with a Cd-free buffer. The development of an absorber layer, transparent conducting oxide window layer, and module design was the key focus. This permitted 1.8% higher efficiency than our last experimental result. The quantity and the injection time of the sodium were controlled, resulting in higher open circuit voltage (V-oc) and short circuit current (J(sc)). In order to increase J(sc), we changed the thickness of the window layer. Boron-doped zinc oxide was optimized for higher transmittance without reducing the fill factor. The uniformity of each layer was improved, and patterns were optimized for each module. Therefore, V-oc, J(sc), and FF could be theoretically improved on the reported results of, respectively, 20 mV,2 mA/cm(2), and 1.4%. The module's efficiency was measured at the Korea Test Laboratory to compare with the data obtained in-house. Various analyses were performed, including secondary ion mass spectroscopy, photoluminescence, quantum efficiency, solar simulator, and UV-vis spectrometry, to measure the cell's depth profile, carrier lifetime, external quantum efficiency, module efficiency, and transmittance, respectively. Copyright (C) 2015 John Wiley & Sons, Ltd.