Modulation of work function of ITO by self-assembled monolayer and its effect on device characteristics of inverted perovskite solar cells

In this work, self-assembled monolayers of a series of para-substituted phenylphosphonic acids were formed on the ITO substrate surface for the fabrication of perovskite-based solar cells. With the perovskite layer directly transferred by a stamping method on the SAM-modified ITO surface, followed by spin-coated PCBM layer, an inverted-type, hole-transport layer-free solar cell was fabricated. The device characteristics, such as open circuit voltage Voc, short circuit current Jsc, and field factor FF, were analyzed with respect to the energy level alignment at the ITO/perovskite interface. The best power conversion efficiency was observed with ITO having work function closest to the valence band maximum of perovskite, giving an efficiency of 13.94 %, considerably higher than the 8.64 % from the bare ITO-based device.