The influence of sequence of precursor films on CZTSe thin films prepared by ion-beam sputtering deposition *Project supported by the National Natural Science Foundation of China (No. 61404086), the Basical Research Program of Shenzhen (Nos. JCYJ20150324140036866, JCYJ20150324141711581), and the Natural Science Foundation of SZU (No. 2014017). (February 2017)