MoOx and V2Ox as hole and electron transport layers through functionalized intercalation in normal and inverted organic optoelectronic devices

To achieve fabrication and cost competitiveness in organic optoelectronic devices that include organic solar cells (OSCs) and organic light-emitting diodes (OLEDs), it is desirable to have one type of material that can simultaneously function as both the electron and hole transport layers (ETLs and HTLs) of the organic devices in all device architectures (i.e., normal and inverted architectures). We address this issue by proposing and demonstrating Cs-intercalated metal oxides (with various Cs mole ratios) as both the ETL and HTL of an organic optoelectronic device with normal and inverted device architectures. Our results demonstrate that the new approach works well for widely used transition metal oxides of molybdenum oxide (MoOx) and vanadium oxide (V2Ox). Moreover, the Cs-intercalated metal-oxide-based ETL and HTL can be easily formed under the conditions of a room temperature, water-free and solution-based process. These conditions favor practical applications of OSCs and OLEDs. Notably, with the analyses of the Kelvin Probe System, our approach of Cs-intercalated metal oxides with a wide mole ratio range of transition metals (Mo or V)/Cs from 1∶0 to 1∶0.75 can offer significant and continuous work function tuning as large as 1.31 eV for functioning as both an ETL and HTL. Consequently, our method of intercalated metal oxides can contribute to the emerging large-scale and low-cost organic optoelectronic devices. Caesium-intercalated metal oxides can act as both hole and electron transport layers in organic optoelectronic devices, shown by a team in China. The use of a single material for both layers will reduce the cost of fabricating organic solar cells (OSCs) and organic light-emitting diodes (OLEDs). The researchers, who are from the University of Hong Kong and the Chinese Academy of Sciences, use molybdenum and vanadium oxides intercalated with different caesium mole ratios for both hole and electron transport layers; previously, these metal oxides have generally been used for the hole transport layer only. The results reveal that these caesium-intercalated metal oxides provide efficient performance and good adaptability for OSCs and OLEDs with both conventional and inverted device architectures. This approach can simplify the fabrication of OSCs and OLEDs and has great potential for organic optoelectronic devices.