A Study on the Effect of Ambient Air Plasma Treatment on the Properties of Methylammonium Lead Halide Perovskite Films

Organic-inorganic halide perovskite materials are considered excellent active layers in the fabrication of highly efficient and low-cost photovoltaic devices. This contribution demonstrates that rapid and low-temperature air-plasma treatment of mixed organic-inorganic halide perovskite film is a promising technique, controlling its opto-electrical surface properties by changing the ratio of organic-to-inorganic components. Plasma treatment of perovskite films was performed with high power-density (25 kW/m(2) and 100 W/cm(3)) diffuse coplanar surface barrier discharge (DCSBD) at 70 degrees C in ambient air. The results show that short plasma treatment time (1 s, 2 s, and 5 s) led to a relatively enlargement of grain size, however, longer plasma treatment time (10 s and 20 s) led to an etching of the surface. The band-gap energy of the perovskite films was related to the duration of plasma treatment; short periods (<= 5 s) led to a widening of the band gap from similar to 1.66 to 1.73 eV, while longer exposure (>5 s) led to a narrowing of the band gap to approx. 1.63 eV and fast degradation of the film due to etching. Surface analysis demonstrated that the film became homogeneous, with highly oriented crystals, after short plasma treatment; however, prolonging the plasma treatment led to morphological disorders and partial etching of the surface. The plasma treatment approach presented herein addresses important challenges in current perovskite solar cells: tuning the optoelectronic properties and manufacturing homogeneous perovskite films.