Search

CZTSSe thin-film absorbers were grown by stacked ZnS/SnS/Cu sputtering with compound targets, and the precursors were annealed in a furnace with a Se atmosphere. We controlled the thickness of the ZnS precursor layer for the CZTSSe thin films in order to reduce the secondary phases and to improve the performance of the devices. The optimal value of the ZnS precursor thickness was determined for the CZTSSe absorbers, and this configuration showed an efficiency of up to 9.1%. In this study, we investigated the depth profiles of the samples in order to determine the presence of secondary phases in the CZTSSe thin films by Raman spectroscopy and Kelvin probe force microscopy. Cu2SnSe3, ZnSe, and MoSe2 secondary phases appeared near the back contact, and the work function distribution of the CZTSSe thin-film surface and the secondary phase distribution were different depending on the depths of the absorber layer. This phase characterization allows us to describe the effects that changes in the thickness of the ZnS precursor can have on the performance of the CZTSSe thin-film solar cells. Although it is important to identify the phases, the effects of secondary phases and point defects are not yet fully understood, even in optimal devices. Therefore, phase identification that is based on the work function and the results obtained from the Raman spectra in terms of the depth profile are instrumental to improve the surface and interface of CZTSSe thin-film solar cells. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin-film solar cells have been fabricated by various methods. Sputtering is one of the vacuum processes that can be used for the growth of the precursors. In this study, CZTSSe thin-films that were fabricated using metal-precursors and with a high efficiency of 12.3% were examined in a comparison with CZTSSe thin-films that were fabricated using compound-precursors, whose efficiency is 9.1%. Especially, the Kelvin probe force microscopy (KPFM) analysis and local current measurement by conductive atomic force microscopy (c-AFM) show that their local electrical properties indicate completely opposite results. The grain boundaries (GBs) has a downward surface potential bending, and this repelled the minority carriers into the intragrains (IGs) in the sample from the metal-precursors. Therefore, we originally verified the differences between the carrier behaviors and the current flows on the surface. [ABSTRACT FROM AUTHOR]

Abstract: Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells are prepared by stacking sputtering of precursors and annealing at Se atmosphere. We achieved the highest conversion efficiency of a CZTSSe thin-film solar cell with 8.06%. Local electrical properties of the CZTSSe films were investigated by Kelvin probe force microscopy. We studied samples which show conversion efficiencies between 3.17% and 8.06%. The CZTSSe thin-film with the highest efficiency exhibits predominantly downward potential bending at grain boundaries (GBs) and upward potential bending at intragrains (IGs). On the other hand, the film with the lowest efficiency shows the opposite behaviors that downward potential bending at GBs and upward potential bending in many regions of IGs. The downward potential bending allows minority carrier collection and reduces recombination at GBs, consequently, enhance current in the solar cell devices. However, some of the GBs possesses deep-level traps so they behave as a hurdle for charge transport, which can be compensated with the carrier motion in the IGs. The results suggest that the potential variations on the GBs and IGs are significantly linked to the carrier transport and device characteristics in the solar cells. [Copyright &y& Elsevier]