Low-Temperature Cross-Linkable Hole-Transport Materials with a Carbazole/Triphenylamine Dual Core: Their Preparation and Device Applications in Solution-Processed OLEDs

Abstract

High-cross-linking temperature is a big challenge involved in solution processing hole-transport materials (HTMs) for multilayer devices. The typical styrene-based HTMs required a high temperature of around 180 °C to form a network. To resolve this problem, we designed a dual-core MCP-type HTM by integrating four carbazole moieties with N³,N³,N³′,N³′-tetraphenyl-[1,1′-biphenyl]-3,3′-diamine, on which four terminal styryl units were connected through a flexible chain, which enables facile in situ cross-linking through photothermally initiating a thiol–ene reaction with pentaerythritol tetrakis(3-mercaptopropionate). The cross-linking temperature was significantly reduced from 180 to 80 °C, which is a record-low temperature for cross-linking styrene terminal HTMs. Through tuning the aliphatic chain length, four cross-linkable HTMs, named V-HBACz, V-OBACz, V-DBACz, and V-DOBACz, were synthesized, with a high-triplet-energy level of up to 2.91 eV, a high thermal decomposition temperature of 430 °C, and a hole mobility of up to 2.4 × 10^–4 cm² V^–1 s^–1. Furthermore, solution-processed thermally activated delayed fluorescence devices with multilayer architecture were prepared based on the newly synthesized HTMs, and a 3-fold improvement in efficiency was achieved in typical 4CzIPN green devices, with a high luminance of 32 016 cd m^–2, a maximum current efficiency of 78.2 cd A^–1, and a maximum external quantum efficiency of 24.5%.