Solution Preparation Of Pure And Doped Metal Oxide Films And Thier Organic Optoelectronic Device Applications

MoO₃and WO₃are two favorable metal oxides utilized in the field of organic optoelectronic devices such as organic light-emitting diodes?OLED?and organic photovoltaics?OPV?,due to their suitable work function,good carrier transport ability,high transmittance and excellent thermal stability.To prepare MoO₃ and WO₃ films for device application,solution methods were preferred,which have the advantages of low cost,simple operation,large area and compitable to flexible substrates.However,there is no report about solution preparation of WO₃ doped MoO₃ films for OLED and OPV devices.The purpose of this work is to prepare MoO₃,WO₃ and WO₃ doped MoO₃films by solution method,and to use them as anode buffers in both OLED and OPV devices.Main works are as follows:1. Employing solution method,MoO₃,WO₃ and WO₃ doped MoO₃ films were prepared and then studied.It was proved that these films were successfully prepared on ITO substrate and exhibited uniform distribution with no cracks,as demonstrated by the SEM image of the WO₃doped MoO₃film.Contact angle test indicated that the surface of metal oxides films were more hydrophobic than the surfaces of PEDOT:PSS,and the surface of WO₃ film had higher hydrophobic than the MoO₃film.Photophysical experment showed that these films have similar and high optical band gap,hence good light transmittance.2. The above prepared films were used as anode buffers in OLEDs and their effects on device performance were investigated.First,a series of devices were investigated with anode buffer of MoO₃film,which were prepared with different MoO₃ dilution solvent and different speed for spin coating.Based on the performances of these devices,the optimized metal oxide concentration and spin-speed for the preparation of the anode buffer comprising MoO₃ was decided.Second,the optimal concentration of WO₃in MoO₃ was achieved by investigating the OLED devices with different WO₃doped MoO₃ anode buffer.It was found that the MoO₃ based OLED showed slightly higher current and quantum efficiencies compared to device without anode buffer,but lower than the PEDOT:PSS based device.When WO₃ was introduced into MoO₃ as anode buffer in OLEDs,improved current and quantum efficiencies?29%and 31%?were achieved compared to PEDOT:PSS based device.Besides,among the OLED devices based on WO₃ doped MoO₃ anode buffer,the driving voltages decrease as the doping concentration increases.Finally,the stability of the device performance was studied.Results showed that inserting MoO₃ or WO₃ film between the ITO and the organic layer helps to improve the stability of the device.3. These pure/doped MoO₃ and WO₃ films were also used as anode buffers in OPVs and their effects on device performance were investigated.First,the spin speed and solution concentration for the preparation of MoO₃ film by spin coating were optimized via corresponding device fabrication and investigation.After that,the effect of WO₃ doping concentration on OPV performance was studied.Results indicated that the device performances were comparable between the OPV based on the optimized MoO₃:WO₃ film and the MoO₃ based one,both of which were higher than the OPV device without anode buffers?2.38%vs 1.73%,2.47%vs 1.73%?.Further study on dark state J-V curves indicated that the optimized MoO3:WO3 film based OPV device has the lowest leakage current and the largest rectification ratio among all the investigated devices,indicating that MoO3:WO3 as anode buffer in OPV device is beneficial to suppress the carrier recombination,hence improve device performance.