Room-temperature photodeposited amorphous VOx hole-transport layers for organic devices

Hole-transport layers (HTL) are an integral part of optoelectronic devices such as organic photovoltaic cells (OPVs) and organic light-emitting diodes (OLEDs). A class of materials commonly used as HTLs are metal oxides because they have high transparency and stability. These metal oxides are, however, often made using techniques that are not conducive to large-scale fabrication, a challenge thatmust be resolved for thewidespread adoption of these devices. In this work, we demonstrate the use of a room-temperature, ambient photochemical deposition route to formvanadium oxide films. We show, using a combination of X-ray absorption and X-ray photoemission spectroscopies, that the VOx film consist of V2O5, but with significant amount of V4+ present. These films are initially created amorphous and become nanocrystalline after annealing in air at a temperature of 250 ◦C. After incorporating these VOx thin films as HTLs in both OPV and OLED devices, we surprisingly find this increase in crystallinity does not translate in improvement in device performance. All devices performsimilarly to – or better – than control devices using PEDOT:PSS as an HTL.We furthermore demonstrate that these films are not affected by the operation of these devices, and that the technique can be employed in combination with slot-die coating printing techniques. This work provides an easily upscaled, low-temperature method for depositing metal-oxide HTL layers.