Vanadium-Substituted Heteropoly Blues as Highly Conductive Hole-Transporting Materials for Efficient Organic Optoelectronic Devices

An applicable hole-transporting layer (HTL) for organic optoelectronic devices should not only possess optimal optoelectronic properties but also offer critical advantages such as versatility, easy availability, and printability for industrial manufacturing. However, the lack of such HTL materials remains a critical bottleneck for further improvements in device performance. In this work, we developed a series of vanadium-substituted heteropoly blues HPB-V1, HPB-V2, and HPB-V3 as HTLs. The introduction of vanadium enables the preferential reduction of V(V) to V(IV) with molybdenum predominantly remaining in its highest oxidation state Mo(VI). This enhances the conductivity of heteropoly blues by more than 5-fold while preserving their high work functions. On the basis of the HPB-V2 HTL, the binary organic solar cell exhibited a photovoltaic efficiency of 20.13%, which is among the top values in the field. Moreover, HPB-V2 is fully compatible with a high-throughput and large-area processing technique, delivering an efficiency of 17.1% in a 1.2 cm 2 device. The incorporation of HPB-V2 also reduces the hole injection barrier in an organic light-emitting diode (OLED), leading to superior luminescent performance and a decreased turn-on voltage from 4.0 to 3.2 V. The results from this work demonstrate the advantages of heteropoly blues in the development of high-performance HTL materials.