Fig. 9
(Reproduced with permission from Ref. [27] Copyright 2016, ©Physical Chemistry Chemical Physics)
a The EL spectra and b the CIE co-ordinates diagram of the undoped PVK based PLEDs with or without different ETLs (DEV B-without ETL, DEV B-BCP, DEV B-Bphen and DEV B-TPBi)