Application Of Solution-processed Molybdenum Oxide In Polymer Solar Cells And Quantum Dot Light-emitting Diodes

ITO is the most commonly used transparent electrode for polymer solar cells(PSCs) and quantum dot light emitting diodes(QLEDs). PEDOT:PSS is the most commonly used anode buffer layer on ITO in PSCs and QLEDs, but the acidic nature of PEDOT:PSS could result in degradation of the performance of the PSCs and QLEDs. To solve this problem, there is graet interest in developing new anode buffer layers to replace PEDOT:PSS. Transition metal oxide(WO3, MoO3, NiO, Cu2 O, ReO3, or V2O5) have been successfully used as anode buffer layers in high performance PSCs. In particular, MoO3 exhibiting remarkably deep lying electronic states and efficient hole-injection into organic materials have been demonstrated. However, their unique electronic properties have so far been primarily achieved using thin films made by high-cost thermal evaporation under vacuum, which presents disadvantages due to the cost issues and incompatibility with roll-to-roll scalable manufacturing.This paper focused on the application of solution-processed molybdenum oxide in polymer solar cell and quantum dot light emitting diodes. The carrier transport efficiency was improved by optimizating the thickness and post processes of Molybdenum Oxide thin films, leading to improved efficiency of PCEs. In the meanwhile, Molybdenum Oxide thin film can effectively balance the recombation of hole and electron in QLEDs. The work in this thesis can be summarized as follows:(1) In the P3HT:PCBM devices based on solution processed MoO_x hole injectiong layer, thickness and post processing of Mo Ox films were optimized to improve the performance of the devices. Performance of the device based on MoO_x is compatible with or even higher than the standard devices based on PEDOT:PSS layers. It could be attributed to the generated gat stetes by vaccum annealing, higher light transmittance and smaller surface roughness. Moreover, the PSCs based on solution processed MoO_x show better stability than standard device. The major degredation came from the decrease of the current devsity of the devices, and the slower degedation could be attribute to the stability of inorganic oxide and the acid and hygroscopicity of PEDOT:PSS.(2)We also optimized the quantum dot light emitting diodes. Then device based on MoO_x hole transport layer were optimized and explored by changing the concentration and annealing condition. We demonstrated that the current efficiency and external quantum efficiency(EQE) of green and red QLEDs based on MoO_x were better than the standard device based on PEDOT:PSS. The current efficiency and EQE of green QLEDs were increased from 11.9 cd/A and 2.9% to 16.1 cd/A and 4.11%. At the same time, the current efficiency of red QLEDs was higher than that of the standard QLEDs in the entire luminous process. We found that the higher performance is mainly due to the more balanced carrier recombination and smoother surface of the the MoO_x hole transport layer compared to that of the PEDOT:PSS layer.(3)All inorganic QLEDs were also demonstrated in this thesis. The device structure is ITO/s-MoO_x/QDs/ZnO/Al, which shows the luminance of 800cd/m2 and current efficiency of 2.94cd/A. Such great device performance could also be attributed to the excellent balance carrier recombination based on MoO_x layer.