Thermally cross-linkable hole-transport materials enable solution-processed blue OLED with LT95 over 150 h

Abstract

The solution-processed method for organic light-emitting diodes (OLEDs) offers the benefits of cost-effectiveness and enhanced material utilization. In the multilayer architecture of solution-processed OLEDs (SOLEDs), the role of hole-transport materials (HTMs) is pivotal for cascade hole injection. However, commercial HTMs such as poly-(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB) are hampered by incompatible energy levels and redissolution with overlayer solvent, prompting the exploration of cross-linkable HTMs (X-HTMs) for better performance. In this study, we have developed two novel small-molecule X-HTMs, N1,N1′-((perfluoropropane-2,2-diyl)bis(4,1-phenylene)) bis(N4,N4-diphenyl-N1-(4-vinylphenyl)benzene-1,4-diamine) (FTPA-V) and N,N′-((perfluoropropane-2,2-diyl) bis-(4,1-phenylene))bis(9-phenyl-N-(4-vinylphenyl)-9H-carbazol-3-amine) (FPCz-V), which incorporate thermally cross-linkable vinyl groups and electron-rich trifluoromethyl units. The X-HTMs enhance interfacial contact through superior film formation and solvent resistance, along with optimal energy levels. The application of X-HTMs significantly enhances the efficiencies and longevities of blue, green, and red SOLEDs. Specially, blue SOLED incorporating FPCz-V exhibits unprecedented lifetime (LT95) extending to over 150 h, setting a new record for blue SOLEDs. The electrochemistry stability, high bond dissociation energy, and triplet energy levels of X-HTMs can effectively minimize exciton annihilation and prolong the lifetime. These findings underscore the potential of X-HTM optimization to propel the development of stable solution-processed luminescent technologies.