Effects of double heat treatment of NiO hole transport layer on the performance of QLEDs

Parameters affecting the performance of QLED devices using NiO hole transport layer (HTL) thin film via the sol-gel process route were investigated. In the preparation of the NiO HTL thin film, a double heat treatment scheme, crystallization heat treatment at elevated temperatures followed by vacuum annealing treatment at lower temperatures, was introduced to form a crystalline NiO single phase as well as surface phases with reduced defect concentration. The decoupling of crystallization and vacuum annealing treatment of NiO HTL thin film was effective in enhancing the performance of the QLEDs. Also, the insertion of an interlayer between QD EML and NiO HTL was very effective in enhancing the performance of the device. With the modification of processing conditions, the luminance of QLED with the NiO HTL was improved from 30 to 11500 cd/m(2)and the current efficiency from 0.25 to 23 cd/A, respectively.