Performance enhancement of perovskite solar cells via modification of the TiO2/perovskite interface with oxygen plasma treatment

High-temperature (similar to 500 degrees C) sintering is a routine post-treatment to fabricate compact Titanium dioxide (TiO2) electron selective layer (ESL) in high-performance perovskite solar cells (PSCs). Here, we propose an effective low-temperature (<150 degrees C) approach: pinhole-free and compact ultrathin TiO2 layers are fabricated via thermal atomic layer deposition (ALD) following a low-pressure oxygen plasma treatment. The hydrophilicity of TiO2 surfaces can be suitably tailored, which favors precursor solution being well spread and the growth of perovskite film. In addition, effective removal of oxygen vacancies serving as unproductive quenching sites in TiO2 surface is observed, which is attributed to atomic oxygen radical, the most reactive species generated in oxygen plasma. The PSC device with oxygen-plasma-treated ALD-TiO2 ESL achieves an efficiency of 14.9%, which is better than 13.3% of the device with 500 degrees C- sintered ALD-TiO2 ESL and comparable to 14.3% of the device with conventional 500 degrees C-sintered Sol-gel-TiO2 ESL under our conditions.