UV ozone treatment for oxidization of spiro-OMeTAD hole transport layer.

For practical application of perovskite photovoltaic devices, it is vital to choose an appropriate carrier extraction material with high mobility, high conductivity, and appropriate molecular energy levels. One of the most frequently used hole transport materials, spiro-OMeTAD, is known to show an improvement in its electrical properties after the oxidation reaction. However, this oxidation reaction is generally accomplished by simple atmospheric exposure, often taking one or more nights under atmospheric conditions, and thus the development of a rapid oxidation strategy without the degradation of device performance is strongly required. Here, we propose a rapid and reproducible oxidation route employing a UV ozone treatment process that enables quick oxidation of spiro-OMeTAD in solution, as short as 30 seconds. Optical and electrical characterization reveals that this method modifies the highest occupied molecular orbital energy level of spiro-OMeTAD to reduce the voltage loss, and also improves the conductivity and mobility, leading to the enhancement in the photovoltaic properties. This finding will provide useful insights into the further development of spiro-OMeTAD-based perovskite solar cell devices.